阅读说明：本技术 氮化物半导体器件及其基板、和稀土元素添加氮化物层的形成方法、以及红色发光器件及其制造方法 (Nitride semiconductor device and substrate therefor, method for forming rare earth element-added nitride layer, red light-emitting device and method for manufacturing same ) 是由 市川修平 藤原康文 馆林润 于 2019-08-30 设计创作，主要内容包括：本发明提供一种氮化物半导体层的制造技术,在偏角倾斜基板上形成氮化物半导体层来制作半导体器件时,不存在与GaN发生混晶化而招致产生晶格应变、晶体缺陷的风险,另外,使用无需持续性添加的材料,来防止宏观台阶的发生,由此能够稳定地供给高品质的半导体器件。一种氮化物半导体器件,其是在基板上设置氮化物半导体层而构成的氮化物半导体器件,基板为偏角倾斜基板,在基板上设有添加有稀土元素的稀土元素添加氮化物层作为基底处理层,在稀土元素添加氮化物层之上设有氮化物半导体层。(The present invention provides a technique for manufacturing a nitride semiconductor layer, which is free from the risk of generating lattice strain and crystal defects due to the mixed crystallization with GaN when a semiconductor device is manufactured by forming the nitride semiconductor layer on an off-angle inclined substrate, and which can stably supply a high-quality semiconductor device by preventing the occurrence of macrosteps using a material that does not require continuous addition. A nitride semiconductor device is formed by providing a nitride semiconductor layer on a substrate, wherein the substrate is an inclined substrate, a rare earth element-added nitride layer to which a rare earth element is added is provided as a base treatment layer on the substrate, and the nitride semiconductor layer is provided on the rare earth element-added nitride layer.)

1. A nitride semiconductor device comprising a substrate and a nitride semiconductor layer provided on the substrate,

the substrate is a declined inclined substrate,

a rare earth element-added nitride layer added with rare earth elements is arranged on the substrate as a base treatment layer,

on the rare earth element-added nitride layer, a nitride semiconductor layer is provided.

2. The nitride semiconductor device according to claim 1,

the rare earth element-doped nitride layer is a layer in which the rare earth element is doped in GaN, InN, AlN, or a mixed crystal of any two or more of these.

3. The nitride semiconductor device according to claim 1 or claim 2,

the addition concentration of the rare earth element in the rare earth element-added nitride layer is 0.001 at% to 10 at%.

4. The nitride semiconductor device according to any one of claims 1 through 3,

the thickness of the rare earth element-added nitride layer is more than 0.1 nm.

5. The nitride semiconductor device according to any one of claims 1 through 4,

the rare earth element is Eu.

6. The nitride semiconductor device according to any one of claims 1 through 5,

the substrate is any one of sapphire, SiC, and Si, or a nitride semiconductor including GaN, InN, AlN, or a mixed crystal of any two or more of these.

7. The nitride semiconductor device according to any one of claims 1 through 6,

the nitride semiconductor device is any of a light emitting device, a high frequency device, and a high output power device.

8. A substrate used in the production of a nitride semiconductor device,

a rare earth element-doped nitride layer doped with a rare earth element is provided on an off-angle substrate.

9. The substrate of claim 8,

the rare earth element-doped nitride layer is a layer in which the rare earth element is doped in GaN, InN, AlN, or a mixed crystal of any two or more of these.

10. The substrate of claim 8 or claim 9,

the addition concentration of the rare earth element in the rare earth element-added nitride layer is 0.001 at% to 10 at%.

11. The substrate according to any one of claims 8 to 10,

the thickness of the rare earth element-added nitride layer is more than 0.1 nm.

12. The substrate according to any one of claims 8 to 11,

the rare earth element is Eu.

13. The substrate according to any one of claims 8 to 12,

the off-angle tilt substrate is any one of sapphire, SiC, and Si, or a nitride semiconductor including GaN, InN, AlN, or a mixed crystal of any two or more of these.

14. A method for forming a rare earth element-added nitride layer on an off-angle substrate, the method comprising:

forming a nitride layer to which a rare earth element is not added on the off-angle substrate; and

a step of forming a rare earth element-added nitride layer on the rare earth element-non-added nitride layer,

the steps are performed by a series of formation steps without taking out the reaction vessel by the metal organic vapor phase epitaxy method,

and the formation of the rare earth element-added nitride layer is performed at a temperature of 900 to 1100 ℃.

15. A substrate, characterized in that,

the rare earth element-doped nitride layer is formed by sequentially laminating a rare earth element-non-doped nitride layer and a rare earth element-doped nitride layer on an off-angle substrate.

16. A method for manufacturing a nitride semiconductor device is provided,

a nitride semiconductor device produced by forming a nitride semiconductor layer on the rare earth element-added nitride layer formed by the method for forming a rare earth element-added nitride layer according to claim 14.

17. A nitride semiconductor device, characterized in that,

the rare earth element-doped nitride layer is formed by sequentially stacking a nitride semiconductor layer, a rare earth element-doped nitride layer, and a rare earth element-undoped nitride layer on an off-angle substrate.

18. A red light-emitting device characterized in that,

the active layer includes: a rare earth element-added nitride layer in which Eu or Pr is added as a rare earth element to GaN, InN, AlN, or a mixed crystal of any two or more of these,

the active layer is formed on the substrate according to any one of claims 8 to 13.

19. A red light-emitting device characterized in that,

a rare earth element-doped nitride layer in which Eu is added as a rare earth element to GaN, InN, AlN, or a mixed crystal of two or more of these elements is formed on an off-angle substrate.

20. A red light-emitting device according to claim 18 or claim 19,

the rare earth element-added nitride layer is a rare earth element-added nitride layer to which oxygen is added together.

21. A method for manufacturing a red light-emitting device according to claim 19,

on the substrate inclined at an angle, a rare earth element-doped nitride layer doped with Eu is formed by an organic metal vapor phase epitaxy method.

Technical Field

The present invention relates to a nitride semiconductor device and a substrate thereof, a method for forming a rare earth element-added nitride layer, a red light-emitting device and a method for manufacturing the same.

Background

In recent years, Light Emitting devices such as Light Emitting Diodes (LEDs) and Laser Diodes (LDs) have been widely used. For example, LEDs are used for various display devices, backlights of liquid crystal displays such as mobile phones, white illumination, and the like, while LDs are used as light sources for blu-ray discs for recording and playing high definition video, optical communication, CDs, DVDs, and the like.

Recently, applications of High-frequency devices such as MMIC (monolithic microwave integrated circuit) and HEMT (High Electron Mobility Transistor) for mobile phones, and High-output power devices such as inverter power transistors and Schottky Barrier Diodes (SBDs) for automobiles have been expanding.

Semiconductor elements constituting these devices are generally manufactured by forming a nitride semiconductor layer of gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN), or the like on a substrate of sapphire or the like.

Conventionally, as a method for forming a nitride semiconductor layer on a substrate, a method of growing a nitride semiconductor layer crystal on (0001) (c-plane) of the substrate has been generally employed, but in this method, piezoelectric polarization occurs due to strain generated during film formation, and there is a problem that device characteristics cannot be obtained as expected at first. That is, as piezoelectric polarization occurs, an internal electric field is generated in the nitride semiconductor layer, and the wave functions of electrons and holes are separated, so that the probability of radiative recombination in the nitride semiconductor layer is reduced, and the desired device characteristics may not be exhibited.

Therefore, it has been studied to improve device characteristics by using a substrate having a surface slightly inclined with respect to the c-plane (off-angle inclined substrate) and growing the substrate in an orientation slightly inclined by several degrees from the [0001] direction along the crystal axis with the slightly inclined surface as a film formation surface to exhibit various advantages such as reduction in crystal defect density and improvement in light emission efficiency in a nitride semiconductor layer (for example, patent document 1).

Fig. 8 is a diagram illustrating crystal growth using the off-angle inclined substrate, and as shown in the lower right great circle of fig. 8, Ga is adsorbed so as to extend along only the central portion of the c-plane adjacent to each other at a distance c, thereby growing a GaN crystal. As shown in the lower center of fig. 8, the c-plane is inclined by an angle θ. As a result, as shown in the upper stage of fig. 8, the step height (thickness of Ga — N monolayer) in the off-angle inclined substrate becomes (c/2), and the terrace width (width in which Ga atoms can diffuse) becomes (c/2tan θ).

However, in the case of this method, it has been clarified that if the off angle is excessively increased in order to achieve a reduction in the crystal defect density, a dramatic improvement in the light emission efficiency, or the like, the mesa width is sharply narrowed, so that a large macro step accompanied by a step aggregation mechanism occurs, and a new problem arises that device characteristics suited to design cannot be obtained in the production of a nitride semiconductor light-emitting device or an electronic device.

Fig. 9 is a diagram specifically showing the relationship between the slip angle and the land width, where the vertical axis represents the land width and the horizontal axis represents the slip angle θ. As can be seen from fig. 9, the width of the mesa is inversely related to the magnitude of the off-angle, and the mesa width sharply decreases from 99.0nm to 14.9nm only when the off-angle θ is changed from 0.15 ° to 1 °. Further, if the width of the terrace is excessively narrowed, step aggregation occurs, and a macro step having a large step height occurs.

When such a macrostep occurs, a strong composition distribution is generated in the crystal when a mixed crystal (for example, AlGaN) is produced due to a difference in introduction efficiency caused by an atomic species (for example, Ga) in the vicinity of the step, and a large influence is exerted on device characteristics when a nanostructure controlled to a size of several nm such as a quantum well structure is produced. In particular, in the field of light emitting devices, there are many problems in practical use, such as difficulty in strictly controlling the emission wavelength.

In addition, even if the surface of the substrate is smoothed by polishing or etching, the macrosteps are formed again when the nitride semiconductor layer is formed thereon, and thus device characteristics conforming to the design cannot be obtained.

Therefore, In order to produce a high-quality and high-performance nitride semiconductor light-emitting device or electronic device In accordance with design, it is considered that a crystal growth technique maintaining a flat surface without macrosteps is indispensable, and for example, a technique of adding indium (In) to nitride has been proposed (non-patent document 1).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2004-335635

Non-patent document

Non-patent document 1: C.K. Shu 4 Another people, Isoelectronic In-doting effect In GaN films grown by metallic chemical vapor deposition, appl.Phys.Lett.73, 641(1998)

Disclosure of Invention

Problems to be solved by the invention

However, it is known that there are various problems with the above-described addition of In. For example, since the addition of In may cause InGaN by mixing with GaN and InGaN formation may cause lattice strain and crystal defects, strict flow control is required. In addition, continuous addition of In is required for removing the macrosteps.

Accordingly, an object of the present invention is to provide a technique for manufacturing a nitride semiconductor layer, which is capable of stably supplying a high-quality semiconductor device by preventing the occurrence of a macro step using a material that does not require continuous addition, without causing a risk of generating lattice strain or crystal defects due to mixed crystallization with GaN, such as In, when the semiconductor device is manufactured by forming the nitride semiconductor layer on an off-angle substrate.

Means for solving the problems

The present inventors succeeded in the world in producing a red light-emitting diode having a light-emitting layer made of a GaN layer (Eu-added GaN layer) to which Eu, which is one of rare earth elements, is added, and reached a far-reaching level with respect to an organometallic vapor phase epitaxy method (OMVPE method) in which the Eu-added GaN layer is controlled at an atomic level.

In this process, the inventors have found that the surface of the Eu-doped GaN layer is planarized, and that Eu has a surfactant effect. Therefore, in the case where a Eu-added GaN layer is provided as a base treatment layer on an off-angle substrate when a semiconductor device is manufactured by forming a nitride semiconductor thin film on the off-angle substrate, it is considered that the surfactant effect of Eu is exerted and the occurrence of macro steps can be prevented in the growth of a nitride semiconductor layer, and various experiments and studies have been made.

As a result, it was found that, even when Eu is added at a low concentration of 1 at% or less, the macro-steps on the surface of the off-angle-tilted substrate are drastically reduced at the time of growth of the Eu-doped GaN layer, and even when a GaN layer to which Eu is not added is grown on the Eu-doped GaN layer at a thickness of more than 5 μm, the flat surface is formed at the atomic level without generating the macro-steps, and the effect of surface flattening by Eu addition is maintained, which is a highly significant academic result.

The mechanism of the phenomenon of preventing the occurrence of macrosteps by adding Eu as described above is now under investigation, but it is assumed that the addition of In promotes the diffusion of Ga atoms to achieve smoothing, whereas Eu inhibits the diffusion of Ga to prevent the occurrence of macrosteps, thereby exhibiting an excellent surfactant effect to smooth the surface of the Eu-added GaN layer and the Eu-non-added GaN layer formed thereon.

Further, the addition of Eu at a low addition concentration of 1 at% or less does not require continuous addition unlike the addition of In. Further, Eu at a low addition concentration is added so as to partially replace Ga of GaN, not to be mixed-crystallized with GaN as In to form InGaN, and therefore, there is no risk of occurrence of crystal defects and strict flow control is not necessary.

In this way, it can be said that the addition of strict flow control and continuity is not necessary in the actual fabrication of a nitride semiconductor device, and the significance is extremely large.

Further, in the present invention, by providing the Eu-doped GaN layer as the undercoat layer, the occurrence of macrosteps can be prevented, and therefore, a nitride semiconductor device suitable not only for a light-emitting device but also for a high-frequency device and a high-power device can be stably supplied.

Further, as a result of further experiments and studies on the preferable concentration of Eu to be added and the preferable thickness of the Eu-added GaN layer, it is found that the preferable concentration of Eu to be added in the Eu-added GaN layer is 0.001 to 10 at%, and the preferable thickness of the Eu-added GaN layer is 0.1nm or more. The upper limit of the thickness of the Eu-doped GaN layer is not particularly limited, but considering saturation of surface smoothing due to the surfactant effect of Eu, it is considered that a sufficient effect can be obtained if the thickness is about 2 μm.

Among the above, GaN is used as the nitride and Eu is used as the additive element, but as a result of further experiments and studies, the present inventors have found that GaN-based nitrides (including mixed crystals of InGaN, AlGaN, and the like) other than GaN, such as AlN and InN, have chemical properties substantially equivalent to GaN and can be similarly used. It is also found that when the additive element is not limited to Eu, and is a rare earth element generally called Sc, Y, and lanthanoid elements from La to Lu, which have substantially the same chemical properties, the same excellent surfactant effect can be exhibited under the same degree of Eu.

As a result of studies on the substrate, it has been found that the same surfactant effect can be obtained by providing a rare earth element-added nitride layer such as an Eu-added nitride layer, even when SiC or Si is used as the substrate in addition to sapphire. SiC has high thermal conductivity and excellent heat release properties, and is therefore suitable for the production of high-power devices. Further, since Si is inexpensive and can easily be obtained in a large size, it is suitable for manufacturing a nitride semiconductor device at a low cost. Further, a nitride semiconductor containing GaN, InN, AlN, or a mixed crystal of any two or more of these is also preferably used.

The invention described in claim 1 to claim 7 is an invention based on the above findings, the invention described in claim 1 is a nitride semiconductor device,

which is a nitride semiconductor device comprising a substrate and a nitride semiconductor layer provided on the substrate,

the substrate is an inclined substrate with an inclined angle,

on the substrate, a rare earth element-doped nitride layer doped with a rare earth element is provided as a base treatment layer,

a nitride semiconductor layer is provided on the rare earth element-added nitride layer.

The invention described in claim 2 relates to the nitride semiconductor device described in claim 1, wherein,

the rare earth element-doped nitride layer is a layer in which the rare earth element is doped in GaN, InN, AlN, or a mixed crystal of any two or more of these.

The invention described in claim 3 is the nitride semiconductor device described in claim 1 or 2, wherein,

the rare earth element is added to the rare earth element-added nitride layer at a concentration of 0.001 to 10 at%.

The invention described in claim 4 is the nitride semiconductor device described in any one of claims 1 to 3, characterized in that,

the thickness of the rare earth element-added nitride layer is 0.1nm or more.

The invention described in claim 5 relates to the nitride semiconductor device described in any one of claims 1 to 4, wherein the nitride semiconductor device is characterized in that,

the rare earth element is Eu.

The invention described in claim 6 relates to the nitride semiconductor device described in any one of claims 1 to 5, wherein the nitride semiconductor device is characterized in that,

the substrate is any one of sapphire, SiC, and Si, or a nitride semiconductor including GaN, InN, AlN, or a mixed crystal of any two or more of these.

The invention described in claim 7 relates to the nitride semiconductor device described in any one of claims 1 to 6, wherein the nitride semiconductor device is characterized in that,

the nitride semiconductor device is any of a light-emitting device, a high-frequency device, and a high-output device.

Among the above, a nitride semiconductor device is produced by providing a rare earth element-added nitride layer as a base treatment layer on an off-angle substrate and then providing a nitride semiconductor layer to which no rare earth element is added. However, the same effect can be obtained by preparing a substrate in which a rare earth element-added nitride layer is formed on an off-angle substrate in advance as a substrate, supplying the substrate to a third party, and then receiving the supply of the third party to grow a nitride semiconductor layer to which no rare earth element is added on the substrate provided with the rare earth element-added nitride layer.

That is, the invention described in claim 8 is a substrate characterized in that,

is a substrate used in the fabrication of nitride semiconductor devices,

a rare earth element-doped nitride layer doped with a rare earth element is provided on an off-angle substrate.

The invention described in claim 9 is a substrate described in claim 8, wherein,

the rare earth element-doped nitride layer is a layer in which the rare earth element is doped in GaN, InN, AlN, or a mixed crystal of any two or more of these.

The invention described in claim 10 is the substrate described in claim 8 or 9, wherein,

the rare earth element is added to the rare earth element-added nitride layer at a concentration of 0.001 to 10 at%.

The invention described in claim 11 is a substrate according to any one of claims 8 to 10, characterized in that,

the thickness of the rare earth element-added nitride layer is 0.1nm or more.

The invention described in claim 12 is the substrate described in any one of claims 8 to 11, wherein,

the rare earth element is Eu.

The invention described in claim 13 is a substrate according to any one of claims 8 to 12, characterized in that,

the off-angle tilt substrate is any one of sapphire, SiC, and Si, or a nitride semiconductor including GaN, InN, AlN, or a mixed crystal of any two or more of these.

The nitride semiconductor device and the rare earth element-added nitride layer on the substrate according to the present invention described above can be produced by: by the metal organic vapor phase epitaxy method (OMVPE method), a rare earth element-free nitride layer and a rare earth element-added nitride layer are formed on an inclined substrate in a series of steps without taking out the substrate from a reaction vessel while changing temperature conditions.

Here, the reason why the rare earth element-non-added nitride layer is formed before the formation of the rare earth element-added nitride layer is that, like sapphire and GaN, the lattice constant is different between the off-angle-inclined substrate and the nitride layer, and when the propagation of crystal defects in the off-angle-inclined substrate is considered, it is preferable to provide the rare earth element-non-added nitride layer between the off-angle-inclined substrate and the rare earth element-added nitride layer. Specifically, it is preferable to provide two rare earth element-free nitride layers, i.e., a low temperature-grown rare earth element-free lt (low temperature) -nitride layer and a high temperature-grown rare earth element-free ud (unaddressed) -nitride layer.

By providing the LT-nitride layer, the off-angle inclined substrate and the nitride layer are matched in lattice constant, and thus, the occurrence of cracks can be prevented. Further, by providing the ud-nitride layer, dislocation as a crystal defect can be suppressed, and a high-quality nitride crystal can be obtained.

Specifically, first, as in the conventional case, an LT-nitride layer and a ud-nitride layer are formed as nitride layers to which no rare earth element is added on an off-angle substrate. And then, changing the temperature to 900-1100 ℃, and forming a rare earth element added nitride layer on the rare earth element non-added nitride layer.

At this time, the surface of the rare earth element-added nitride layer is planarized by the surfactant effect of the added rare earth element. Therefore, even when a nitride semiconductor device is produced by providing a nitride semiconductor layer on the rare earth element-added nitride layer as the underlying treatment layer, a nitride semiconductor device exhibiting excellent device characteristics can be stably supplied without generating a macrostep.

Further, the formation of the nitride layer to which no rare earth element is added (LT-nitride layer, ud-nitride layer), the formation of the rare earth element-added nitride layer, and the formation of the nitride semiconductor layer can be performed by merely setting whether or not the temperature condition is changed and whether or not the rare earth element is added at the time of the growth of each nitride layer, and therefore, the formation can be performed in a series of steps without taking out the nitride layer from the reaction vessel.

In addition, among the above, a nitride semiconductor device can be produced by forming a nitride semiconductor layer on a substrate before forming a rare earth element-added nitride layer.

The invention described in claims 14 to 17 is an invention based on the above findings, and the invention described in claim 14 is a method for forming a rare earth element-added nitride layer, characterized in that,

a method for forming a rare earth element-added nitride layer on an off-angle substrate, comprising:

forming a nitride layer to which no rare earth element is added on the substrate having the off-angle slope; and

a step of forming a rare earth element-added nitride layer on the rare earth element-non-added nitride layer,

the above steps are performed in a series of formation steps without taking out the reaction vessel by the metal organic vapor phase epitaxy method, and

the rare earth element-added nitride layer is formed at a temperature of 900 to 1100 ℃.

The invention according to claim 15 is a substrate, wherein,

the rare earth element-doped nitride layer is formed by sequentially laminating a rare earth element-non-doped nitride layer and a rare earth element-doped nitride layer on an off-angle substrate.

The invention described in claim 16 is a method for manufacturing a nitride semiconductor device,

a nitride semiconductor layer is formed on the rare earth element-added nitride layer formed by the method for forming a rare earth element-added nitride layer according to claim 14, thereby manufacturing a nitride semiconductor device.

The invention according to claim 17 is a nitride semiconductor device, wherein,

the rare earth element-doped nitride layer is formed by sequentially stacking a nitride semiconductor layer, a rare earth element-doped nitride layer, and a rare earth element-undoped nitride layer on an off-angle substrate.

As described above, the present inventors succeeded in the world in producing a red light-emitting diode having a Eu-doped GaN layer as an active layer (light-emitting layer), but the expectation for further improvement in the emission intensity is increasing.

In the course of research on further improvement of the emission intensity in such a red light-emitting diode, the present inventors have considered that, in a light-emitting device utilizing emission of rare earth ions, such as a red light-emitting diode having an Eu-doped GaN layer as an active layer, high-concentration doping of a rare earth element directly contributes to increase of the emission intensity, and therefore, a crystal growth technique capable of adding a rare earth element at a high concentration is indispensable, and have conducted specific research.

As a result, it was found that, in the thin film growth of a nitride semiconductor, when the Eu-doped GaN layer as an active layer is grown by inclining the crystal axis by several degrees from the [0001] direction, that is, by using an off-angle substrate, a strong step flow growth mechanism can be obtained, and thus Eu can be doped at a high concentration.

Specifically, it was found that when a Eu-added GaN layer is grown on a slightly inclined surface of an off-angle substrate, a strong step flow growth mechanism is induced to promote step flow growth over the entire surface, and therefore, Eu is efficiently introduced into an active layer even at an Eu/Ga ratio of 2.4% in excess of the Eu/Ga flow ratio (Eu/Ga ratio) which is considered to be the optimum growth condition for growth of the Eu-added GaN layer on a coaxial substrate, and the Eu-added GaN layer is grown while maintaining the quality (high crystallinity) of the GaN film, and extremely excellent emission intensity can be obtained.

That is, in the growth of the Eu-doped GaN layer on the conventional coaxial substrate, as the Eu addition concentration increases, a unique hillock structure is generated on the surface and easily becomes a rough growth surface, and as a result, the crystal quality is lowered, and the improvement of the emission intensity is hindered. In addition, in a high current injection state, that is, in a highly excited state, the emission intensity is saturated, and a so-called efficiency drop phenomenon occurs. Therefore, in the formation of the Eu-added GaN layer, 2.4% of the Eu/Ga ratio has been considered as an optimum growth condition in the past, but in the present invention, as described above, the formation of the hillock structure associated with Eu addition is suppressed by growing the Eu-added GaN layer by increasing the Eu/Ga ratio on an off-angle inclined substrate, and the Eu-added GaN layer into which Eu is introduced at a high concentration is formed, whereby extremely excellent emission intensity can be obtained.

In the case where O is added together with Eu, the variation in local structure around Eu of the active layer is greatly reduced, the emission spectrum (PL spectrum) is sharpened, and the emission intensity is further improved.

Further, such a red light emitting device can be produced using an off-angle tilted substrate on which the above-described base treatment has been performed in advance, but since the base treatment layer is also a Eu-doped GaN layer, it is preferable to directly form the Eu-doped GaN layer on the off-angle tilted substrate. That is, since the Eu-doped GaN layer formed in the initial stage functions as a ground layer of the off-angle substrate and the Eu-doped GaN layer formed thereon functions as an active layer, the ground layer and the active layer can be formed in a series of steps in the environment in which the ground layer is formed, and more efficient formation of the active layer can be achieved. Further, efficient use of Eu is enabled, and thus a high material gain can be obtained.

Such a significant improvement in emission intensity can be similarly obtained even when Pr is used as an additive rare earth element instead of Eu. In this case, the Pr-doped GaN layer may be formed directly on the off-angle substrate, but it is preferable to form the Pr-doped GaN layer as an active layer on the off-angle substrate subjected to the foundation treatment in advance.

The invention described in claim 18 to claim 22 is an invention based on the above-mentioned findings, and the invention described in claim 18 is a red light-emitting device characterized in that,

the active layer includes: a rare earth element-added nitride layer in which Eu or Pr is added as a rare earth element to GaN, InN, AlN, or a mixed crystal of any two or more of these,

the active layer is formed on the substrate according to any one of claims 8 to 13.

Further, the invention described in claim 19 is a red light emitting device characterized in that,

a rare earth element-added nitride layer in which Eu is added as a rare earth element to GaN, InN, AlN, or a mixed crystal of two or more of these elements is formed on an off-angle substrate.

The invention described in claim 20 relates to the red light emitting device described in claim 18 or 19, wherein the red light emitting device is characterized in that,

the rare earth element-added nitride layer is a rare earth element-added nitride layer to which oxygen is added in common.

The invention described in claim 21 is a method for manufacturing a red light-emitting device, characterized in that,

the method of manufacturing a red light-emitting device according to claim 19,

on the substrate inclined at an angle, a rare earth element-doped nitride layer doped with Eu is formed by an organic metal vapor phase epitaxy method.

Effects of the invention

According to the present invention, when a semiconductor device is manufactured by forming a nitride semiconductor layer on an off-angle substrate, there is no risk of generating lattice strain or crystal defects due to the mixed crystallization with GaN as In, and furthermore, by preventing the occurrence of macrosteps by using a material that does not require continuous addition, it is possible to provide a technique for manufacturing a nitride semiconductor layer that can stably supply a high-quality semiconductor device.

Drawings

Fig. 1 is a schematic diagram showing a structure of a nitride semiconductor device according to an embodiment of the present invention.

Fig. 2 is a diagram showing a flow of forming a nitride semiconductor device in one embodiment of the present invention.

Fig. 3 is a graph showing the results of in-situ observation of the reflection intensity from the surface of laser light irradiated to a growing GaN layer in one embodiment of the present invention, where (a) is the result of observation in an off-angle tilted substrate, and (b) is the result of observation in an on-axis substrate.

Fig. 4 is a view showing the results of observing the surface of each Eu-unadditized GaN layer after growth by an optical microscope (upper stage) and an AFM microscope (lower stage) in one embodiment of the present invention, (a) is the result of observation on an on-axis substrate, and (b) is the result of observation on an off-angle tilted substrate.

Fig. 5 is a graph showing the results of in-situ observation of the reflection intensity of laser light with respect to the GaN layer being grown, in one embodiment of the present invention, wherein (a) is the result of observation in a declined substrate, and (b) is the result of observation in a coaxial substrate.

Fig. 6 is a view showing the results of observation of the surface of the coating layer by an AFM microscope, wherein (a) is the result of observation on the in-line substrate, and (b) is the result of observation on the off-angle inclined substrate.

Fig. 7 is a view showing the results of observation of the surface of the sample having the Eu-added GaN layer provided on the off-angle tilted substrate by (a) an optical microscope and (b) an AFM microscope in one embodiment of the present invention.

Fig. 8 is a diagram illustrating crystal growth using an off-angle inclined substrate.

Fig. 9 is a diagram showing a relationship between the deflection angle and the land width.

Fig. 10 is a schematic diagram showing a structure of a red light-emitting device on which a Eu-added GaN layer is formed.

Fig. 11 is an optical microscope image of the surface of the Eu and O co-doped GaN layer formed using the coaxial substrate.

Fig. 12 is a diagram illustrating the difference in the surface state of the Eu and O co-doped GaN layer formed using the off-angle tilted substrate and the coaxial substrate.

Fig. 13 is a graph showing the results of measuring the PL spectrum of a red light-emitting device in which a Eu-doped GaN layer is formed on a coaxial substrate and a bias-angle tilted substrate at room temperature, where (a) shows the relationship between the PL spectrum intensity (a.u.) and the wavelength (nm) (when He — Cd laser light and 5mW excitation are used), and (b) shows the relationship between the excitation energy (mW) and the PL integrated intensity (a.u.) at wavelengths 610 to 650 nm.

Detailed Description

The present invention will be described below with reference to the accompanying drawings by way of specific embodiments. In the following description, a sapphire substrate is taken as an example of the off-angle inclined substrate, GaN is taken as an example of the nitride, and Eu is taken as an example of the rare earth element, but the present invention is not limited thereto as described above.

1. Nitride semiconductor device

Fig. 1 is a schematic view showing the structure of the nitride semiconductor device according to the present embodiment. In fig. 1, 10 denotes a sapphire substrate, 40 denotes a Eu-added GaN layer (GaN: Eu), and a cap layer 50 is formed on the Eu-added GaN layer 40. The cap layer 50 is an Eu-undoped GaN layer (ud-GaN) serving as a nitride semiconductor layer.

In the present embodiment, since the Eu-doped GaN layer 40 to which Eu that exhibits excellent surfactant effect is added is provided as a base treatment layer in forming the cap layer 50, the cap layer 50 can be grown on the Eu-doped GaN layer 40 in which the occurrence of macro steps is prevented, and even if the thickness exceeds 5 μm, the surface can be grown while forming a flat surface at an atomic level. Further, the crystal growth effect by using the off-angle inclined substrate, which is originally expected, can be sufficiently exhibited, and the device characteristics can be improved.

As described above, in the present embodiment, the effect of surface planarization on the Eu-added nitride layer provided as the undercoat layer is maintained also in the cap layer (nitride semiconductor layer) formed on the upper layer, and therefore, a nitride semiconductor device suitable not only as a light emitting device but also as a high frequency device or a high power device can be stably supplied.

In the present embodiment, as shown in fig. 1, two kinds of Eu-unadditized GaN layers, i.e., an LT-GaN layer 20 grown at a low temperature of about 475 ℃ and an Eu-unadditized GaN layer (ud-GaN)30 grown at a high temperature of about 1180 ℃ are provided between a sapphire substrate 10 and a Eu-added GaN layer 40. As described above, by providing the LT-GaN layer 20, the sapphire crystal and the GaN crystal can be matched in lattice constant, and the occurrence of cracks can be prevented. Further, by providing the ud-GaN layer 30, the influence of dislocation as a crystal defect can be suppressed, and the occurrence of defects in the Eu-doped GaN layer can be controlled.

2. Method for forming nitride semiconductor device

Next, a method for forming the nitride semiconductor device will be described. Fig. 2 is a diagram showing a flow of forming the nitride semiconductor device in this embodiment. In fig. 2, the upper stage shows the gas supplied as the raw material and the supply rate, and the lower stage shows the relationship between the growth temperature (vertical axis) and the time (horizontal axis).

In this embodiment, the OMVPE method is used for forming a nitride semiconductor device. Trimethyl gallium (TMGa) is used as the Ga material, and ammonia (NH) is used as the N material₃). Further, as the Eu raw material, a carrier gas (hydrogen gas: H) is used₂) Bubbled n-propyltetramethylcyclopentadienyl europium (Eu [ C ]₅(CH₃)₄(C₃H₇)]₂：EuCp^pm ₂)。

As shown in fig. 1, an LT-GaN layer 20, a ud-GaN layer 30, a Eu-doped GaN layer 40, and a cap layer 50 are sequentially formed on a sapphire substrate 10 according to the flow shown in fig. 2. Hereinafter, a detailed description will be given based on fig. 1 and 2.

(1) Formation of LT-GaN layer 20

First, the sapphire substrate 10 inclined at an off-angle of 1 ° was placed in a reaction vessel adjusted to a pressure of 104kPa, and then NH was supplied into the reaction vessel with the temperature in the reaction vessel set to 475 ℃₃Gas (223mmol/min) and TMGa gas (52.1. mu. mol/min) were used to form the LT-GaN layer 20 having a thickness of 30nm on the sapphire substrate 10at a growth rate of 1.3. mu.m/h.

(2) Formation of ud-GaN layer 30

Next, the temperature in the reaction vessel was 1180 ℃ and NH was supplied into the reaction vessel₃Gas (179mmol/min) and TMGa gas (102. mu. mol/min) at a growth rate of 3.2. mu.m/h formed a ud-GaN layer 30 with a thickness of 2 μm on the LT-GaN layer 20.

(3) Formation of Eu-added GaN layer 40

Next, the temperature in the reaction vessel was set to 960 ℃ and NH was supplied into the reaction vessel₃Gas (es)(179mmol/min), TMGa gas (25.6. mu. mol/min), and EuCp^pm ₂Gas (0.586. mu. mol/min), Eu-added GaN layer 40 having a thickness of 40nm was formed on ud-GaN layer 30 at a growth rate of 0.78. mu.m/h.

(4) Formation of the capping layer 50

Next, the temperature in the reaction vessel was set to 1180 ℃ again, and NH was supplied into the reaction vessel₃The gas (179mmol/min) and TMGa gas (102. mu. mol/min) were used to form a capping layer 50 having a thickness of 5 μm on the Eu-added GaN layer 40 at a growth rate of 3.2 μm/h as a nitride semiconductor device.

Of the above, EuCp having a high vapor pressure is used as a raw material of Eu^pm ₂Eu (C) may be used₁₁H₁₉O₂)₃、Eu[C₅(CH₃)₅]₂、Eu[C₅(CH₃)₄H]₂And the like.

3. Evaluation of

(1) Confirming the occurrence of macrosteps in an off-angle inclined substrate

As an evaluation sample, a Eu non-GaN layer having a thickness of 7.6 μm was grown by the OMVPE method on a sapphire substrate inclined at an off-angle of 1 ° (off-angle inclined substrate). On the other hand, for comparison, an Eu non-GaN layer having a thickness of 7.6 μm was grown on a sapphire substrate (coaxial substrate) which was not tilted in the same manner.

Then, each GaN layer being grown was irradiated with laser light having a wavelength of 633nm, and the reflection intensity from the surface was observed in situ. The results are shown in FIG. 3. In fig. 3, (a) is an observation result of an off-angle tilt substrate, and (b) is an observation result of an on-axis substrate, where the left vertical axis represents the reflection intensity (arbitrary unit), the right vertical axis represents the crystal growth temperature (c), and the horizontal axis represents the crystal growth time (min).

In the case of a coaxial substrate, as shown in fig. 3(b), the reflection intensity is high as a whole, and a constant level is maintained even if the crystal growth time is long. On the other hand, in the case of the off-angle inclined substrate, as shown in fig. 3(a), it is understood that the reflection intensity becomes lower as a whole, and the reflection intensity further decreases as the crystal growth time becomes longer. This is considered to be because the nitride layer is formed on the off-angle inclined substrate, and therefore the flatness on the surface of the nitride layer is low, and the flatness is further reduced as the film thickness becomes larger.

The surface of each Eu-non-GaN-added layer after growth was observed by an optical microscope and an AFM microscope (atomic force microscope) to evaluate the surface state. The results are shown in FIG. 4. In fig. 4, the upper stage shows the observation result by the optical microscope, the lower stage shows the observation result by the AFM microscope, and the left side shows the observation result in the (a) coaxial substrate and the right side shows the observation result in the (b) off-angle inclined substrate.

As shown in fig. 4, in the case of the coaxial substrate, no macrosteps were observed, and the surface was flat. On the other hand, in the case of a substrate inclined at an off-angle, it is observed that a large macro-step is generated by step aggregation, and a wavy structure is generated on the surface, thereby deteriorating flatness.

(2) Evaluation of flatness on Eu-not-added GaN layer

Next, as an evaluation sample, an LT-GaN layer having a thickness of 30nm, a ud-GaN layer having a thickness of 2 μm, a Eu-doped GaN layer having a thickness of 40nm, and a cap layer (ud-GaN layer) having a thickness of 5 μm were grown on the same substrates (off-angle tilt substrate and coaxial substrate) as described above. On the other hand, for comparison, the ud-GaN layer was grown on each substrate until the total thickness became the same.

Further, as described above, the reflection intensity during growth of each layer was observed in situ, and the surface state of each GaN layer at the uppermost layer after growth was observed by an AFM microscope and an optical microscope, and evaluated.

The observation results of the reflection intensity are shown in fig. 5. In fig. 5, the upper stage is (a) the observation result in the off-angle inclined substrate, the lower stage is (b) the observation result in the coaxial substrate, the left side is the observation result in all steps, and the right side is the observation result in the growth of the cap layer. The solid line shows the observation result of the sample having the Eu-doped GaN layer, and the broken line shows the observation result of the sample having only the ud-GaN layer.

In the case of the coaxial substrate, as shown in fig. 5(b), the reflection intensity in the sample having the Eu-doped GaN layer does not change much from the reflection intensity in the sample having only the ud-GaN layer, and is maintained at a constant level even if the crystal growth time is long. On the other hand, in the case of the off-angle inclined substrate, as shown in fig. 5(a), by providing the Eu-doped GaN layer, the reflection intensity is drastically improved as compared with the sample of only the ud-GaN layer. From the results, it is understood that the growth of the Eu-doped GaN layer greatly affects the improvement of the flatness when the cap layer is formed.

Fig. 6 shows the result of observing the surface of the coating layer by an AFM microscope. Here, the results of observation of the sample provided with the Eu-doped GaN layer are shown, where (a) is the result of observation of the on-axis substrate, and (b) is the result of observation of the off-angle tilted substrate.

As is clear from fig. 6, the Eu-doped GaN layer is provided on the off-angle tilted substrate, and the surface state is substantially the same as that of the coaxial substrate.

Fig. 7 shows the results of (a) optical microscope and (b) AFM microscope observation of the surface of the sample having the Eu-doped GaN layer on the off-angle tilted substrate.

As is clear from fig. 7, by providing the Eu-doped GaN layer, the surface of the cap layer is smoothed, and the surface roughness RMS thereof becomes 0.15nm and very small. This result indicates that the occurrence of macro steps is prevented by the addition of Eu, a GaN layer having a flat surface at an atomic level is formed, and excellent surfactant effect of Eu is exhibited.

Among the above, the surfactant effect was explained by taking an example in which the Eu-added GaN layer was grown on the off-angle tilted substrate and the cap layer was provided thereon, but the Eu-added GaN layer and the ud-GaN layer may be stacked in pairs a plurality of times, whereby the surface state can be further smoothed.

4. Application to semiconductor devices

As described above, in this embodiment, by providing the Eu-added GaN layer on the off-angle tilted substrate, a substrate with low defect density can be provided. Therefore, blue and green LEDs with high luminous efficiency can be realized dramatically as compared with conventional ones. Further, since a low dislocation density is realized on the off-angle inclined substrate, an element with less leakage current can be realized, and a highly reliable nitride power device can be manufactured.

5. Red light emitting device

Next, the red light emitting device according to the present embodiment will be described in detail.

(1) Problems of the prior art

First, problems in the growth of the Eu-doped GaN layer on the conventional coaxial substrate will be described, and specifically, the reason why the optimal growth condition of the Eu-doped GaN layer is considered to be that the Eu/Ga ratio is 2.4% will be described.

First, as a sample for evaluation, a red light-emitting device having a GaN layer in which Eu and O are added together was fabricated on a coaxial substrate such that the Eu/Ga ratio was 2.4%, 3.5%, and 7.1%.

Specifically, initially, non-additive GaN layers (LT-GaN layer and ud-GaN layer) having a thickness of about several μm were grown on a coaxial sapphire substrate, and thereafter, TMGa was introduced as a Ga raw material and NH was introduced as an N raw material₃EuCp bubbled with carrier gas (supplied with oxygen) is introduced as Eu raw material at a predetermined Eu/Ga ratio^pm ₂And growing a GaN layer by adding Eu and O with the thickness of about 300nm together. Finally, a ud-GaN layer having a thickness of 10nm was grown to complete the fabrication of three red light emitting devices (see fig. 10).

Fig. 11 is an optical microscope image of the surface of the Eu and O co-doped GaN layer formed in the obtained three samples for evaluation. As is clear from fig. 11, in the case of the coaxial sapphire substrate, the surface flatness was lost as the Eu/Ga ratio became larger at 2.4%, 3.5%, and 7.1%, and particularly, the crystal growth surface was drastically deteriorated when the Eu/Ga ratio was changed from 3.5% to 7.1%.

In the upper stage of fig. 12, the surface state of the Eu-O co-doped GaN layer obtained in both cases of the Eu/Ga ratio of 3.5% and 7.1% is shown by increasing the magnification of the optical microscope from fig. 11. As is clear from fig. 12, when the Eu and O co-doped GaN layer is formed on the coaxial substrate, the active layer grows spirally, and as the Eu/Ga ratio becomes higher, a large number of spiral hillocks are formed, resulting in surface roughness.

Fig. 13 shows the results of measuring the PL spectrum of the Eu-doped GaN layer formed on the coaxial substrate at room temperature. In fig. 13, (a) shows the relationship between PL spectral intensity (a.u.) and wavelength (nm) (when He — Cd laser and 5mW excitation are performed), and (b) shows the relationship between excitation energy (mW) and PL integrated intensity (a.u.) at wavelengths 610 to 650 nm.

As is clear from FIG. 13(a), in the case of the coaxial substrate, as the Eu/Ga ratio becomes higher, the emission center becomes larger⁵D₀→⁷F₂The light emission peak of (2) rises. However, as shown in FIG. 13(b), even if the Eu/Ga ratio is increased under strong excitation, the saturation phenomenon of light emission is enhanced, and the emission intensity is slightly reduced when the Eu/Ga ratio is 7.1% as compared with the case of 3.5%.

Therefore, considering also the surface state of the Eu-doped GaN layer, conventionally, the optimal growth condition for growing the Eu-doped GaN layer on a coaxial substrate is that the Eu/Ga ratio is 2.4%, which is considered to be problematic for further increasing the Eu/Ga ratio.

(2) Eu-added GaN layer formed on off-angle tilted substrate

Next, as this embodiment, a surface state and emission intensity in the case of forming a Eu-added GaN layer on an off-angle tilted substrate will be described.

The present inventors have focused on the fact that a strong step flow growth mechanism can be obtained when crystal growth is performed in an orientation slightly inclined by several degrees from the [0001] direction along the crystal axis during thin film growth of a nitride semiconductor, and have formed a Eu-doped GaN layer on an off-angle substrate.

Specifically, two types of red light emitting devices having Eu/Ga ratios of 3.5% and 7.1% were fabricated on a slightly inclined (0001) sapphire substrate having an off-angle of 2 ° in the m-axis direction, in the same manner as on the above-described coaxial substrate.

The lower part of fig. 12 shows the surface state of the obtained Eu and O co-doped GaN layer. As is clear from fig. 12, in the case of the off-angle inclined substrate, the growth of the active layer is not performed by the spiral growth but by the step flow growth, and therefore, the formation of the spiral hillock is suppressed, and the active layer is grown while maintaining high crystallinity even if the Eu/Ga ratio is high.

FIG. 13 also shows the PL spectrum measurement results of a Eu-doped GaN layer formed at an Eu/Ga ratio of 3.5% on an off-angle tilted substrate. As is clear from fig. 13(a), when the substrate is tilted at an off-angle, even if the Eu/Ga ratio is 3.5%, a strong emission intensity that is not obtained with the coaxial substrate is obtained. As is clear from fig. 13(b), the saturation phenomenon of the emission is suppressed, and the emission intensity is improved by 2.04 times as compared with the conventional coaxial substrate (Eu/Ga ratio of 2.4%).

It was confirmed that such improvement of emission intensity is because, even with the same Eu/Ga ratio, introduction of Eu into the active layer is improved and the Eu concentration in the Eu-added GaN layer is increased, and therefore, by forming the Eu-added GaN layer on the off-angle inclined substrate, the Eu-added GaN layer having a high Eu concentration can be formed, and it is expected as a method for realizing improvement of emission intensity.

(3) The red light emitting device according to this embodiment mode has practical applicability

As described above, in the red light emitting device according to the present embodiment, since the Eu-doped GaN layer having a high Eu concentration can be formed on the off-angle substrate, and the strong emission intensity can be directly reflected, a high-efficiency red light emitting device can be manufactured, and a high-luminance light emitting diode can be realized by applying the red light emitting device to a semiconductor LED in the visible light region developed mainly from GaN-based materials. In addition, in recent years, in the development of a laser diode having a rare earth-doped semiconductor layer including a red light-emitting layer as an active layer, high material gain can be achieved by adding a rare earth element such as Eu at a high concentration.

The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments. Various modifications can be made to the above-described embodiments within the same or equivalent scope of the present invention.

Description of the reference numerals

10 sapphire substrate

20 LT-GaN layer

30 ud-GaN layer

40 Eu-doped GaN layer

50 coating

c c distance between faces

Theta off angle