阅读说明：本技术 一种基于氮化镓单晶衬底的激光二极管及其制备方法 (Laser diode based on gallium nitride single crystal substrate and preparation method thereof ) 是由 贾传宇 凌东雄 王红成 吕伟 王春华 康晓娇 胡西多 于 2019-09-29 设计创作，主要内容包括：本发明公开了一种基于氮化镓单晶衬底的激光二极管及其制备方法,所述激光二极管包括从下到上依次层叠设置的GaN单晶衬底、n型GaN层、n型限制层、下波导层、复合量子阱有源区、电子阻挡层、上波导层、p型限制层和p型GaN层。本发明设计和优化氮化镓基激光器高量子效率应力调控有源区结构,新型光波导层结构以及新型限制层结构,在低位错密度GaN单晶衬底上制备激光二极管,突破GaN基激光器的外延制备技术难点,得到高可靠性高量子效率GaN基激光器。(The invention discloses a laser diode based on a gallium nitride single crystal substrate and a preparation method thereof, wherein the laser diode comprises a GaN single crystal substrate, an n-type GaN layer, an n-type limiting layer, a lower waveguide layer, a composite quantum well active region, an electronic barrier layer, an upper waveguide layer, a p-type limiting layer and a p-type GaN layer which are sequentially stacked from bottom to top. The invention designs and optimizes a high quantum efficiency stress regulation active region structure, a novel optical waveguide layer structure and a novel limiting layer structure of the gallium nitride-based laser, prepares a laser diode on a GaN single crystal substrate with low dislocation density, breaks through the technical difficulty of epitaxial preparation of the GaN-based laser, and obtains the GaN-based laser with high reliability and high quantum efficiency.)

1. A laser diode based on a gallium nitride single crystal substrate is characterized by comprising a GaN single crystal substrate (101), an n-type GaN layer (102), an n-type limiting layer (103), a lower waveguide layer (104), a composite quantum well active region (105), an electron blocking layer (106), an upper waveguide layer (107), a p-type limiting layer (108) and a p-type GaN layer (109) which are sequentially stacked from bottom to top;

the compounding amountThe sub-well active region (105) comprises a shallow well and a light emitting region which are sequentially stacked from bottom to top, wherein the shallow well is In 2-6 periods_x1Ga_1-x1The shallow well comprises an N/GaN superlattice structure, wherein the well layer of the shallow well is 2-3 nm thick, and the barrier layer of the shallow well is 2-5 nm thick; the luminous zone is a composite barrier layer/In with 2-6 periods_xGa_1-xN/composite barrier layer structure, the composite barrier layer is In_x2Ga_1-x2N/GaN/In_x2Ga_1-x2N structure, the total thickness of the composite barrier layer is 5-11 nm In_xGa_1-xThe thickness of the N well layer is 3-5 nm; in the composite barrier layer_x2Ga_1-x2N is 0.5-1 nm thick, and In is In the composite barrier layer_x2Ga_1-x2N is symmetrically distributed on the upper side and the lower side of the GaN, and the thickness of the GaN in the composite barrier layer is 4-9 nm; the In component content x1, x2 and x satisfy 0 < x2 < x1 < x < 1.

2. The laser diode according to claim 1, wherein the n-type confinement layer (103) is a three-gradient n-AlGaN/GaN superlattice composite confinement layer, and comprises a first gradient of the n-type confinement layer, a second gradient of the n-type confinement layer and a third gradient of the n-type confinement layer which are sequentially stacked from bottom to top; the first gradient of the n-type confinement layer is n-Al with 30-50 periods_y1Ga_{1- y1}N/GaN superlattice, N-Al in first gradient of N-type confinement layer_y1Ga_1-y1The thicknesses of N and GaN are both 3 nm; the second gradient of the n-type confinement layer is n-Al with 30-50 periods_y2Ga_1-y2N/GaN superlattice, N-Al in second gradient of N-type confinement layer_y2Ga_1-y2The thicknesses of N and GaN are both 2.5 nm; the third gradient of the n-type confinement layer is n-Al with 30-50 periods_y3Ga_1-y3N/GaN superlattice, N-Al in third gradient of N-type confinement layer_y3Ga_1-y3The thicknesses of N and GaN are both 2 nm; the Al component contents of y1, y2 and y3 meet the requirements that y1 is more than 0.05 and more than y2 and more than y3 and less than 0.15; SiH₄As an n-type doping source, the doping concentration of Si is 10¹⁸～10¹⁹cm^-3。

3. The laser diode of claim 2, wherein said diode is a diodeThe lower waveguide layer (104) is n-In with u-GaN +15 periods_x3Ga_1-x3The N/GaN superlattice + N-GaN composite structure is characterized In that the u-GaN thickness of the lower waveguide layer is 15-25 nm, and the N-In thickness of the lower waveguide layer_x3Ga_1-x3The well layer thickness of the N/GaN superlattice is 2-2.5 nm, and the N-In of the lower waveguide layer_x3Ga_1-x3The thickness of the barrier layer of the N/GaN superlattice is 2-2.5 nm, and the thickness of the N-GaN of the lower waveguide layer is 25-40 nm; the In component content x3 is less than the In component x In the active region; SiH₄As an n-type doping source, the doping concentration of Si is 10¹⁸～10¹⁹cm^-3。

4. The laser diode of claim 3, wherein the electron blocking layer (106) comprises a first gradient of an electron blocking layer and a second gradient of an electron blocking layer which are sequentially stacked from bottom to top, the first gradient of the electron blocking layer is u-GaN + 4-6 periods of u-AlGaN/InGaN superlattice, the thickness of the u-GaN of the first gradient of the electron blocking layer is 5-6 nm, the thickness of the AlGaN layer of the first gradient of the electron blocking layer is 1.5-2.0 nm, and the thickness of the InGaN layer of the first gradient of the electron blocking layer is 2-2.5 nm;

the second gradient of the electron blocking layer is u-GaN + p-AlGaN/InGaN superlattice with 8-10 periods, the thickness of the u-GaN of the second gradient of the electron blocking layer is 4-5 nm, the thickness of the AlGaN layer in the second gradient of the electron blocking layer is 2-3 nm, and the thickness of the InGaN layer in the second gradient of the electron blocking layer is 3-4 nm.

5. A laser diode as claimed In claim 4, characterized In that the upper waveguide layer (107) is p-GaN + p-In_x4Ga_1-x4The N/GaN superlattice composite structure is characterized In that the thickness of p-GaN In the upper waveguide layer is 25-40 nm, and the p-In of the upper waveguide layer_x4Ga_1-x4The thickness of a well layer In the N/GaN superlattice is 2-2.5 nm, and the p-In of the upper waveguide layer_x4Ga_1-x4The thickness of the barrier layer in the N/GaN superlattice is 2-2.5 nm; the In component content x4 is less than the In component x In the active region; magnesium cyclopentadienyl is used as p-type doping source, and the Mg doping concentration is 10¹⁷～10¹⁸cm^-3。

6. The laser diode of claim 5, wherein the p-type confinement layer (108) is a three-gradient p-AlGaN/GaN superlattice composite confinement layer, and comprises a first gradient of the p-type confinement layer, a second gradient of the p-type confinement layer and a third gradient of the p-type confinement layer which are sequentially stacked from bottom to top; the first gradient of the p-type limiting layer is p-Al with 30-50 periods_z1Ga_{1- z1}N/GaN superlattice, N-Al in first gradient of p-type confinement layer_z1Ga_1-z1The thicknesses of N and GaN are both 2 nm; the second gradient of the p-type limiting layer is n-Al with 30-50 periods_z2Ga_1-z2N/GaN superlattice, N-Al in second gradient of p-type confinement layer_z2Ga_1-z2The thicknesses of N and GaN are both 2.5 nm; the third gradient of the p-type limiting layer is n-Al with 30-50 periods_z3Ga_1-z3N/GaN superlattice, N-Al in third gradient of p-type confinement layer_z3Ga_1-z3The thicknesses of N and GaN are both 3 nm; the Al component contents z1, z2 and z3 meet the requirements that z3 is more than 0.05 and more than z2 and more than z1 and more than 0.15; magnesium cyclopentadienyl is used as p-type doping source, and the Mg doping concentration is 10¹⁷～10¹⁸cm^-3。

7. The laser diode according to claim 6, wherein the p-type GaN layer (109) has a thickness of 100-150 nm; magnesium cyclopentadienyl is used as p-type doping source, and the Mg doping concentration is 10¹⁷～10¹⁸cm^-3。

8. The laser diode according to claim 7, wherein the n-type GaN layer has a thickness of 2-4 μm; SiH₄As an n-type doping source, the doping concentration of Si is 10¹⁸～10¹⁹cm^-3。

9. A method of making a laser diode as claimed in claim 8, comprising the steps of:

s1, carrying out surface activation treatment on a GaN single crystal substrate (101) in a mixed atmosphere of hydrogen and ammonia at the temperature of 900-1100 ℃;

s2, introducing trimethyl gallium as a group III source, ammonia as a group V source and SiH in a hydrogen atmosphere at the temperature of 950-1200 DEG C₄Growing an n-type GaN layer (102) on a GaN single crystal substrate (101) as an n-type doping source;

s3, introducing trimethyl gallium, trimethyl aluminum and trimethyl indium as III group sources, ammonia as V group source, SiH in a hydrogen atmosphere at 850-1050 DEG C₄As an n-type doping source, growing an n-type limiting layer (103) on the n-type GaN layer (102);

s4, introducing trimethyl gallium and trimethyl indium as III group sources, ammonia as V group source and SiH in nitrogen atmosphere at 820-850 DEG C₄Growing a lower waveguide layer (104) on the n-type confinement layer (103) as an n-type doping source;

s5, in a nitrogen atmosphere, introducing trimethyl gallium as a III group source and ammonia as a V group source at the temperature of 750-850 ℃, and growing a composite quantum well active region (105) on the lower waveguide layer (104);

s6, in a nitrogen atmosphere, introducing trimethyl gallium, trimethyl aluminum and trimethyl indium as III-group sources, ammonia as V-group sources and magnesium as p-type doping sources at the temperature of 850-880 ℃, and growing an electron blocking layer (106) on the composite quantum well active region (105);

s7, in a nitrogen atmosphere, introducing trimethyl gallium and trimethyl indium as III group sources, ammonia as V group sources, and magnesium cyclopentadienyl as p-type doping sources at 820-850 ℃, and growing an upper waveguide layer (107) on the electron blocking layer (106);

s8, introducing trimethyl gallium, trimethyl aluminum and trimethyl indium as III-group sources, ammonia as V-group sources and magnesium chloride as p-type doping sources in a hydrogen atmosphere at 850-1050 ℃, and growing a p-type limiting layer (108) on the upper waveguide layer (107);

and S9, introducing trimethyl gallium serving as a III-group source and ammonia serving as a V-group source and magnesium metallocene serving as a p-type doping source in a hydrogen atmosphere at the temperature of 950-980 ℃, and growing a p-type GaN layer (109) on a p-type limiting layer (108) to obtain the laser diode.

10. The method of claim 9, wherein the steps S1 to S9 are performed in a metal-organic compound vapor phase epitaxy reaction chamber.

Technical Field

The invention relates to the technical field of laser diodes, in particular to a laser diode based on a gallium nitride single crystal substrate and a preparation method thereof.

Background

The III-V group nitride semiconductor material is a third generation semiconductor material following silicon and gallium arsenide, comprises gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN) and alloys thereof, is a direct band gap semiconductor, and has the advantages of large forbidden bandwidth (in the range of 0.7-6.2eV), high breakdown electric field, high thermal conductivity, high electron saturation rate, strong radiation resistance, chemical corrosion resistance and the like. These advantages in optoelectronic properties make III-V nitride materials have a very strong competitive advantage in optoelectronic fields (such as LEDs and LDs), are irreplaceable, and are ideal materials for fabricating semiconductor lasers in the ultraviolet to green wavelength bands.

The GaN-based green laser has great scientific research value, economic value and market prospect. The GaN-based green laser is one of laser display three primary color light sources, and has important application value and wide market prospect in the fields of laser films, laser televisions, laser projection, laser illumination, biomedicine, material processing, optical communication, optical storage, medical treatment and cosmetology, scientific research and national defense, instruments and detection, image recording, entertainment and the like. The most attractive application field of the GaN-based green laser is laser display, which is a hotspot in the research field of nitride devices at home and abroad at present.

With the rapid development of laser display technology, the demand for GaN-based lasers has become more urgent. However, the GaN-based laser has low quantum efficiency, and needs to be further improved in terms of lifetime, reliability and stability. Chinese patent application 201610183087.X discloses a stress-regulating waveguide layer green laser epitaxial wafer, the substrate of which is GaN, the light-limiting factor and quantum efficiency of which are not high enough to satisfy the current demand. Therefore, it is necessary to develop a GaN-based laser diode having high quantum efficiency.

Disclosure of Invention

In order to overcome the defect of low quantum efficiency of the green laser in the prior art, the invention provides the laser diode based on the gallium nitride single crystal substrate, and the provided laser diode has high quantum efficiency and long service life.

The invention also aims to provide a preparation method of the laser diode based on the gallium nitride single crystal substrate.

In order to solve the technical problems, the invention adopts the technical scheme that:

a laser diode based on a gallium nitride single crystal substrate comprises a GaN single crystal substrate, an n-type GaN layer, an n-type limiting layer, a lower waveguide layer, a composite quantum well active region, an electron blocking layer, an upper waveguide layer, a p-type limiting layer and a p-type GaN layer which are sequentially stacked from bottom to top;

the composite quantum well active region comprises a shallow well and a light emitting region which are sequentially stacked from bottom to top, wherein the shallow well is In 2-6 periods_x1Ga_1-x1The shallow well comprises an N/GaN superlattice structure, wherein the well layer of the shallow well is 2-3 nm thick, and the barrier layer of the shallow well is 2-5 nm thick; the luminous zone is a composite barrier layer/In with 2-6 periods_xGa_1-xN/composite barrier layer structure, the composite barrier layer is In_x2Ga_1-x2N/GaN/In_x2Ga_1-x2N structure, the total thickness of the composite barrier layer is 5-11 nm In_xGa_1-xThe thickness of the N well layer is 3-5 nm; in the composite barrier layer_x2Ga_1-x2N is 0.5-1 nm thick, and In is In the composite barrier layer_x2Ga_1-x2N is symmetrically distributed on the upper side and the lower side of the GaN, and the thickness of the GaN in the composite barrier layer is 4-9 nm; the In component content x1, x2 and x satisfy 0 < x2 < x1 < x < 1.

In the application, the quantum well active region shallow well structure can effectively improve the current expansion in the horizontal direction and simultaneously has the effect of storing electrons. The light-emitting area composite barrier structure can effectively reduce lattice mismatch between light-emitting area well barriers and a piezoelectric polarization field generated by thermal mismatch, and improve electron hole composite light-emitting efficiency.

Preferably, the n-type confinement layer is a three-gradient n-AlGaN/GaN superlattice composite confinement layer from bottom to topThe n-type limiting layer first gradient, the n-type limiting layer second gradient and the n-type limiting layer third gradient are sequentially stacked; the first gradient of the n-type confinement layer is n-Al with 30-50 periods_y1Ga_1-y1N/GaN superlattice, N-Al in first gradient of N-type confinement layer_y1Ga_1-y1The thicknesses of N and GaN are both 3 nm; the second gradient of the n-type confinement layer is n-Al with 30-50 periods_y2Ga_1-y2N/GaN superlattice, N-Al in second gradient of N-type confinement layer_y2Ga_1-y2The thicknesses of N and GaN are both 2.5 nm; the third gradient of the n-type confinement layer is n-Al with 30-50 periods_y3Ga_1-y3N/GaN superlattice, N-Al in third gradient of N-type confinement layer_y3Ga_1-y3The thicknesses of N and GaN are both 2 nm; the Al component contents of y1, y2 and y3 meet the requirements that y1 is more than 0.05 and more than y2 and more than y3 and less than 0.15; SiH₄As an n-type doping source, the doping concentration of Si is 10¹⁸～10¹⁹cm^-3。

Preferably, the lower waveguide layer is n-In with u-GaN +15 periods_x3Ga_1-x3The N/GaN superlattice + N-GaN composite structure is characterized In that the u-GaN thickness of the lower waveguide layer is 15-25 nm, and the N-In thickness of the lower waveguide layer_x3Ga_1-x3The well layer thickness of the N/GaN superlattice is 2-2.5 nm, and the N-In of the lower waveguide layer_x3Ga_1-x3The thickness of the barrier layer of the N/GaN superlattice is 2-2.5 nm, and the thickness of the N-GaN of the lower waveguide layer is 25-40 nm; the In component content x3 is less than the In component x In the active region; SiH₄As an n-type doping source, the doping concentration of Si is 10¹⁸～10¹⁹cm^-3。

Preferably, the electron blocking layer comprises a first gradient of the electron blocking layer and a second gradient of the electron blocking layer which are sequentially stacked from bottom to top, the first gradient of the electron blocking layer is u-GaN + 4-6 periods of u-AlGaN/InGaN superlattice, the thickness of the u-GaN of the first gradient of the electron blocking layer is 5-6 nm, the thickness of the AlGaN layer of the first gradient of the electron blocking layer is 1.5-2.0 nm, and the thickness of the InGaN layer of the first gradient of the electron blocking layer is 2-2.5 nm;

the second gradient of the electron blocking layer is u-GaN + p-AlGaN/InGaN superlattice with 8-10 periods, the thickness of the u-GaN of the second gradient of the electron blocking layer is 4-5 nm, the thickness of the AlGaN layer in the second gradient of the electron blocking layer is 2-3 nm, and the thickness of the InGaN layer in the second gradient of the electron blocking layer is 3-4 nm.

Preferably, the upper waveguide layer is p-GaN + p-In_x4Ga_1-x4The N/GaN superlattice composite structure is characterized In that the thickness of p-GaN In the upper waveguide layer is 25-40 nm, and the p-In of the upper waveguide layer_x4Ga_1-x4The thickness of a well layer In the N/GaN superlattice is 2-2.5 nm, and the p-In of the upper waveguide layer_x4Ga_1-x4The thickness of the barrier layer in the N/GaN superlattice is 2-2.5 nm; the In component content x4 is less than the In component x In the active region; magnesium cyclopentadienyl is used as p-type doping source, and the Mg doping concentration is 10¹⁷～10¹⁸cm^-3。

Preferably, the p-type confinement layer is a three-gradient p-AlGaN/GaN superlattice composite confinement layer, and comprises a first gradient of the p-type confinement layer, a second gradient of the p-type confinement layer and a third gradient of the p-type confinement layer which are sequentially stacked from bottom to top; the first gradient of the p-type limiting layer is p-Al with 30-50 periods_z1Ga_1-z1N/GaN superlattice, N-Al in first gradient of p-type confinement layer_z1Ga_1-z1The thicknesses of N and GaN are both 2 nm; the second gradient of the p-type limiting layer is n-Al with 30-50 periods_z2Ga_1-z2N/GaN superlattice, N-Al in second gradient of p-type confinement layer_z2Ga_1-z2The thicknesses of N and GaN are both 2.5 nm; the third gradient of the p-type limiting layer is n-Al with 30-50 periods_z3Ga_1-z3N/GaN superlattice, N-Al in third gradient of p-type confinement layer_z3Ga_1-z3The thicknesses of N and GaN are both 3 nm; the Al component contents z1, z2 and z3 meet the requirements that z3 is more than 0.05 and more than z2 and more than z1 and more than 0.15; magnesium cyclopentadienyl is used as p-type doping source, and the Mg doping concentration is 10¹⁷～10¹⁸cm^-3。

Preferably, the thickness of the p-type GaN layer is 100-150 nm; magnesium cyclopentadienyl is used as p-type doping source, and the Mg doping concentration is 10¹⁷～10¹⁸cm^-3。

Preferably, the thickness of the n-type GaN layer is 2-4 μm; SiH₄As an n-type doping source, the doping concentration of Si is 10¹⁸～10¹⁹cm^-3。

The invention also provides a preparation method of the laser diode, which comprises the following steps:

s1, carrying out surface activation treatment on a GaN single crystal substrate in a mixed atmosphere of hydrogen and ammonia at the temperature of 900-1100 ℃;

s2, introducing trimethyl gallium as a group III source, ammonia as a group V source and SiH in a hydrogen atmosphere at the temperature of 950-1200 DEG C₄As an n-type doping source, growing an n-type GaN layer on a GaN single crystal substrate;

s3, introducing trimethyl gallium, trimethyl aluminum and trimethyl indium as III group sources, ammonia as V group source, SiH in a hydrogen atmosphere at 850-1050 DEG C₄As an n-type doping source, growing an n-type limiting layer on the n-type GaN layer;

s4, introducing trimethyl gallium and trimethyl indium as III group sources, ammonia as V group source and SiH in nitrogen atmosphere at 820-850 DEG C₄As an n-type doping source, growing a lower waveguide layer on the n-type limiting layer;

s5, in a nitrogen atmosphere, introducing trimethyl gallium as a group III source and ammonia as a group V source at the temperature of 750-850 ℃, and growing a composite quantum well active region on the lower waveguide layer;

s6, introducing trimethyl gallium, trimethyl aluminum and trimethyl indium as III group sources, ammonia as V group sources and magnesium as p-type doping sources in a nitrogen atmosphere at 850-880 ℃, and growing an electron blocking layer on the active region of the composite quantum well;

s7, in a nitrogen atmosphere, introducing trimethyl gallium and trimethyl indium as III group sources, ammonia as V group sources, and magnesium cyclopentadienyl as p-type doping sources at 820-850 ℃, and growing an upper waveguide layer on the electron blocking layer;

s8, introducing trimethyl gallium, trimethyl aluminum and trimethyl indium as III group sources, ammonia as V group sources and magnesium chloride as p-type doping sources in a hydrogen atmosphere at 850-1050 ℃, and growing a p-type limiting layer on the upper waveguide layer;

and S9, introducing trimethyl gallium as a III group source and ammonia gas as a V group source and magnesium metallocene as a p-type doping source in a hydrogen atmosphere at the temperature of 950-980 ℃, and growing a p-type GaN layer on the p-type limiting layer to obtain the laser diode.

And S9, after the step is finished, annealing. And the annealing step is specifically that after the epitaxial growth is finished, the temperature of the reaction chamber is reduced to 700-750 ℃, the annealing treatment is carried out for 5-20 min in a pure nitrogen atmosphere, and then the temperature is reduced to room temperature, so that the growth is finished.

Preferably, steps S1 to S9 are performed in a metal organic compound vapor phase epitaxy reaction chamber.

Preferably, in the step S1, the temperature is raised to 500-700 ℃ in a hydrogen atmosphere, then ammonia gas is introduced to form a mixed atmosphere of hydrogen gas and ammonia gas, the temperature is raised to 900-1100 ℃, and surface activation treatment is carried out on the GaN single crystal substrate. In the step S1, the time for carrying out surface activation treatment on the GaN single crystal substrate can be 3-15 min.

Compared with the prior art, the invention has the beneficial effects that:

(1) by adopting the multi-gradient AlGaN/GaN superlattice limiting layer structure, the effect of accumulation of internal stress of the AlGaN/GaN superlattice along with increase of the growth period number can be effectively relieved, and the crack-free epitaxial material with high crystal quality is obtained.

(2) Compared with the traditional GaN or InGaN waveguide layer structure, the composite waveguide layer structure can relieve the piezoelectric polarization field in the subsequent growth active region while regulating and controlling the optical limiting factor.

(3) The quantum well active region shallow well structure can effectively improve the current expansion in the horizontal direction and simultaneously has the effect of storing electrons. The light-emitting area composite barrier structure can effectively reduce lattice mismatch between light-emitting area well barriers and a piezoelectric polarization field generated by thermal mismatch, and improve electron hole composite light-emitting efficiency.

(4) By adopting the composite electron barrier layer structure, the hole injection efficiency can be effectively improved, and the quantum efficiency in the active region can be improved.

Drawings

Fig. 1 is a schematic structural diagram of a laser diode based on a gallium nitride single crystal substrate according to the present invention.

Fig. 2 shows the result of the optical pumping of the laser diode based on the gallium nitride single crystal substrate according to embodiment 1 of the present invention.

Fig. 3 shows the result of the optical pumping of the laser diode based on the gallium nitride single crystal substrate according to embodiment 2 of the present invention.

Fig. 4 is a result of optical pumping lasing of a laser diode based on a gallium nitride single crystal substrate of comparative example 1.

Detailed Description

The present invention will be further described with reference to the following embodiments.