High efficiency oxidized VCSEL with improved light extraction and method of fabricating the same
阅读说明：本技术 具有改进的光提取性的高效率氧化型vcsel及其制造方法 (High efficiency oxidized VCSEL with improved light extraction and method of fabricating the same ) 是由 李亨株 于 2019-06-26 设计创作，主要内容包括：本发明涉及一种垂直腔面发射激光器(VCSEL)及其制造方法,更详细地,涉及一种发射峰值波长为860nm的激光的高效率氧化型垂直腔面发射激光器及其制造方法。(The present invention relates to a Vertical Cavity Surface Emitting Laser (VCSEL) and a method of manufacturing the same, and more particularly, to a high efficiency oxide VCSEL emitting laser light having a peak wavelength of 860nm and a method of manufacturing the same.)
1. An oxidized vertical cavity surface emitting laser characterized in that,
laser light having a peak wavelength of 860 + -10 nm is transmitted between the upper electrode and the upper DBR,
and a conductive current diffusion layer having a lower refractive index than the upper distributed Bragg reflector and having a roughened upper surface.
2. An oxidized vertical cavity surface emitting laser according to claim 1, wherein said current diffusion layer is a GaP layer.
3. An oxidized vertical cavity surface emitting laser according to claim 1 or 2,
the GaP layer includes a metal and/or a non-metal dopant.
4. An oxidized vertical cavity surface emitting laser according to claim 3,
the dopant is one or more selected from the group consisting of Mg, Zn, and carbon.
5. An oxidized vertical cavity surface emitting laser according to claim 1 or 2,
the thickness of the current diffusion layer is 1 [ mu ] m or more.
6. An oxidized vertical cavity surface emitting laser according to claim 1 or 2,
the rough surface layer is a rough surface layer formed by wet etching or dry etching.
7. An oxidized vertical cavity surface emitting laser according to claim 1 or 2,
the roughness of the rough surface layer is +/-1 mu m.
8. An oxidized vertical cavity surface emitting laser according to claim 1 or 2,
the organic light emitting diode comprises a lower electrode, a substrate, a lower distributed Bragg reflector, an active layer, an upper distributed Bragg reflector, an upper electrode and an oxide layer.
9. An oxidized vertical cavity surface emitting laser according to claim 1 or 2,
the active layer is composed of a GaAs quantum well layer and an AlGaAs quantum barrier layer,
the upper and lower DBRs are of AlxGa1-xAs layer and AlyGa1-yDistributed Bragg reflector with As layer alternately and repeatedly stacked structure, wherein the thickness of the As layer is 0.8<x<1，0<y<0.2，
The oxide layer is composed of an annular peripheral oxide layer and an inner current window in a central circle shape,
the upper electrode is a ring-shaped electrode.
10. An oxidized vertical cavity surface emitting laser according to claim 8,
the oxide layer is located between layers of the upper p-DBR.
11. An oxidized vertical cavity surface emitting laser according to claim 9,
the oxidized VCSEL operates under the current of 10-40 mA.
12. An oxidized vertical cavity surface emitting laser according to claim 9,
the upper electrode is a ring-shaped multilayer electrode including a Pt layer.
13. An oxidized vertical cavity surface emitting laser according to claim 9,
the oxidized VCSEL further includes an anti-reflection layer over the current diffusion layer.
14. A method for manufacturing an oxide VCSEL,
GaP layer with thickness of 1 μm or more and rough surface formed on the upper surface is formed between the upper electrode and upper DBR of the oxidation type VCSEL with peak wavelength of 860 + -10 nm.
Technical Field
The present invention relates to a Vertical Cavity Surface Emitting Laser (VCSEL) and a method of manufacturing the same, and more particularly, to a high efficiency oxide type VCSEL which emits a large amount of laser light having a peak wavelength of 860nm due to improved light extraction, and a method of manufacturing the same.
Background
Although the efficiency of a general Vertical Cavity Surface Emitting Laser (VCSEL) is lower than that of the conventional side Emitting Laser, since Laser light is emitted in a Vertical direction, it can be used in the field of the conventional light Emitting diode, thereby having high marketability.
As shown in fig. 1, the VCSEL10 has a structure in which a
Typically, the trench 9 is a circular trench and is formed by dry etching (dry etching) technique. The
Therefore, in the manufacturing process, a current window (oxide aperture) and upper and lower DBRs are necessary for the characteristics of the resonant laser, but there is a problem in that the materials used in these two places are the same material, and the uppermost portion of the upper p-DBR is oxidized (oxidation) together with the current window in the oxidation process for forming the current window, resulting in a high probability of occurrence of defects. The oxidation process being H implantation2O vapor, Al to be used as a current window0.98Ga0.02A process in which Al of the As layer is reacted with high-temperature water vapor to thereby produce an AlxOy layer, but Al is used As the materialxGa1-xAs/AlyGa1-yThe upper and lower DBRs formed of As contain Al, and thus, a portion is oxidized together.
Fig. 2a is a Scanning Electron Microscope (SEM) image showing the DBR damage pattern occurring during oxidation, and when p-metal is applied to the DBR damaged sample, electrode peeling (peeling) or current injection unevenness (efficiency reduction) may occur later. Fig. 2b shows the shape of the current window, the black band shapes being trench (recessed) regions, the middle regions being the columnar regions emitting light, the brighter parts being the oxidized parts. The central, dim circular portion is the light emitting area where light is directly emitted, and will also be labeled as the aperture (aperture) in the VCSEL.
The conventional VCSEL injects a low current because it generates a large amount of heat in the element when a high current is turned on due to its resonance characteristic, thereby often causing element damage caused by the turn-on of the high current, which makes it impossible to expect a current amplification effect of the current injected in the electrode. Therefore, the current discharged from the upper electrode located at the edge of the upper DBR does not uniformly pass through the current window in the central portion, which causes a problem of a decrease in efficiency.
An oxide type VCSEL having a peak wavelength of 850nm is disclosed in korean laid-open patent KR10-2018-0015630(WO 2016/198282), and various methods of forming a plurality of oxide layers inside an upper DBR are disclosed in order to improve the VCSEL. This leads to non-uniformity in reflectivity of the upper DBR during fabrication, and also causes process complications such as the need to reprocess the oxide material used to create the multiple current windows.
In addition, as a scheme capable of uniformly passing the current discharged from the upper electrode through the current window in the center portion, a transparent ITO layer is formed on the entire upper DBR, and the current discharged from the annular electrode is uniformly supplied to the center portion through the ITO.
In addition, the oxide VCSEL has a disadvantage in that the generated resonance wavelength has some local light emitting regions, and the light extraction efficiency is also lowered due to the upper DBR located at the uppermost portion.
Disclosure of Invention
Technical problem to be solved
The technical problem to be solved by the present invention is to provide a method for preventing the damage of the upper DBR during the manufacturing process of the oxide VCSEL.
Another technical problem to be solved by the present invention is to provide a method of stably guiding a current flow and diffusion from an upper electrode of a VCSEL to a light emitting region to fabricate an oxidized VCSEL.
Another technical problem that the present invention is intended to solve is to prevent damage of an upper DBR during oxidation of an oxide VCSEL and stably guide current flow and diffusion from an upper electrode to a light emitting region while providing a transparent high-conductivity barrier layer to light emitted from the oxide VCSEL.
Another technical problem that the present invention is intended to solve is to cover an upper DBR in an oxidized VCSEL, thereby preventing damage of the upper DBR during oxidation and stably guiding current flow and diffusion from an upper electrode to a light emitting region, while providing a transparent high-conductivity barrier layer for light emitted from the oxidized VCSEL and providing a thickness that significantly improves the efficiency of the oxidized VCSEL.
Another technical problem that the present invention is intended to solve is to provide a technique of maximally activating a partial light-emitting region and more efficiently extracting light emitted from the light-emitting region to the outside to increase the efficiency of the VCSEL.
(II) technical scheme
In order to solve the above-described problems, the present invention provides an oxide type vertical cavity surface emitting laser, which transmits laser light having a peak wavelength of 860 ± 10nm (hereinafter referred to as 'peak wavelength of 860 nm') between an upper electrode and an upper dbr, and has a conductive current diffusion layer having a refractive index lower than that of the upper dbr, and a rough surface formed on an upper surface thereof.
Although not limited in theory, the non-roughened current spreading layer improves the fluidity of the current supplied from the upper electrode to the current window, and the thicker the current supplied, the more remarkable the improvement in the fluidity of the current is, but if the thickness is sufficient to provide sufficient current flow, no better improvement is produced, but the roughened current spreading layer prevents the phenomenon that the laser light generated based on sufficient current flow is totally reflected from the surface to the inside to be not extracted, and thus the improvement limit of the non-roughened current spreading layer can be overcome.
In the present invention, laser is understood to mean a wavelength with half-height-width-at-half-maximum (FHMW) amplitude less than 5 nm.
In the present invention, the current diffusion layer is preferably a non-oxide type barrier (barrier) layer so as to cover an upper DBR (distributed bragg reflector) layer during the oxidation of the VCSEL, thereby being capable of preventing damage during the oxidation.
In the practice of the present invention, the current diffusion layer may be a conductive GaP layer which has a relatively high transparency to laser light having a peak wavelength of 860nm and is formed with a rough surface on the upper portion so as to improve the efficiency of the oxide VCSEL when stacked, in order to prevent oxidation by water vapor without including an Al (Al free) layer having an Al component.
In the present invention, the roughened surface of the upper surface of the GaP layer may be formed by etching the upper surface of the GaP layer. The etching may utilize wet etching or dry etching, and the roughness (roughness) of the etched surface may be > ± 1 μm.
In the practice of the present invention, the GaP rough surface can be wet etched by mixing an acid system such as hydrochloric acid or sulfuric acid, and dry etched by using a mixed gas of a BCl system gas and an Ar gas and an etching apparatus to which plasma of RF power is applied.
In the present invention, the GaP layer having an upper rough surface may include a metal or non-metal dopant in order to improve conductivity. The metal dopant is, for example: manganese (Mg), zinc (Zn), and the non-metallic dopant may be carbon (c).
In the present invention, the thickness of the roughened GaP layer is preferably 1 μm or more so that current can sufficiently diffuse. If the thickness is small, the diffusion of current may be insufficient, and the efficiency of the oxide VCSEL according to the introduction of the current diffusion layer is slightly improved.
In the present invention, it is preferable that the thickness of the current diffusion layer is increased to a thickness (saturation thickness) that does not produce an efficiency improvement effect according to the increase in thickness due to saturation. In the practice of the present invention, the saturation thickness may be 3 μm with a current window of 10 μm in diameter.
In the present invention, the oxidized Vertical Cavity Surface Emitting Laser (VCSEL) may include a lower electrode, a substrate, a lower Distributed Bragg Reflector (Distributed Bragg Reflector), an active layer, an upper Distributed Bragg Reflector, an upper electrode, and an oxide layer.
In the present invention, the active layer of the VCSEL is an active layer that can emit light having a peak wavelength of 850 ± 10nm (hereinafter referred to as 'peak wavelength of 850 nm'). In one embodiment of the invention, the active layer may include a GaAs quantum well layer and an AlGaAs quantum barrier layer.
In the present invention, the upper and lower distributed bragg reflectors are configured to resonate light emitted from the active layer and reflect the light in the vertical direction.
In the present invention, the upper and lower DBRs may be DBRs in which a pair of reflective layers composed of a high refractive layer and a low refractive layer are repeatedly stacked to be able to reflect light emitted from the active layer and light reflected from the opposite-side reflector.
In the practice of the present invention, in order to make it possible to substantially completely reflect light reflected by the active layer and the upper DBR, the lower DBR uses 30 or more pairs of n-DBRs, preferably 40 pairs of n-DBRs, and in order to improve the light emission possibility, the upper DBR may have 5 to 10 pairs less than the lower DBR, preferably, may be a p-DBR consisting of 20 to 25 pairs.
In an embodiment of the present invention, the upper and lower dbr may be made of Al having a high refractive indexxGa1-xAs layer and Al with low refractive indexyGa1-yBragg reflector with As layer alternate and repeated laminated structure, wherein 0.8<x<1，0<y<0.2。
In the present invention, the oxidized layer is composed of an oxidizing substance, and may refer to a layer in which a region oxidized for resonance and a non-oxidized region coexist. The oxide layer may be Al in order to be easily oxidized by high-temperature water vaporzGa1-zAs, wherein 0.95<z is less than or equal to 1. The oxide layer is oxidized from the periphery to the center, and the oxide layer can be formed by a ring-shaped oxide layer and a current window in the shape of an inner central circleAnd (4) forming.
In the present invention, the diameter of the center circle forming the current window in the oxide layer needs to be narrow to the extent that laser light can be emitted, and preferably, the diameter thereof may be 10 μm or less.
In the present invention, the oxide layer may be located at an upper portion of the active layer, and preferably, may be located inside the upper p-DBR, and preferably, may be located between layers forming the p-DBR, in order not to affect the active layer. More preferably, the lower end of the upper p-DBR, for example, in the upper DBR, may be located between the first and second pairs of the lower end, and may have a thickness of 30-100 nm.
In the implementation of the invention, the oxidized VCSEL can be operated under the current of 10-40 mA, preferably, the operating range is 25-35 mA, and most preferably, the oxidized VCSEL can be operated under the current of 30-35 mA. When the current is less than 10mA, no laser light is generated, and when the current exceeds 40mA, no laser light having a peak wavelength of 860nm is generated due to the influence of heat generation.
In the present invention, the upper electrode may be formed in a ring shape, and preferably, may be a multi-layered electrode formed of Au/Pt/Ti, in order not to shield the emitted light. In one embodiment, the electrodes may be about 2 μm or so.
In the present invention, the oxidized VSCEL may further include a reflection preventing layer to be able to prevent reflection of the emitted light. The reflection preventing layer may cover the current diffusion layer and be located between the current diffusion layer and the upper electrode. In addition, the reflection preventing layer may cover upper portions of the upper electrode and the current diffusion layer and be positioned at an uppermost portion of the oxide type VCSEL.
In the practice of the present invention, the anti-reflection layer may be formed of SiN or SiO and grown to a thickness of about 100 to 500 nm. Preferably, the thickness is 150 to 400nm, and more preferably, the thickness is 200 to 300 nm.
In one aspect of the present invention, there is provided a method of manufacturing an oxide VCSEL, wherein a GaP layer having a thickness of 1 μm or more is formed between an upper electrode and an upper DBR of the oxide VCSEL having a peak wavelength of 860 nm.
(III) advantageous effects
According to the present invention, a new current diffusion layer having a barrier function is provided, which can protect the upper DBR during oxidation, improve current flow, and transmit light of the VCSEL of 860 nm.
The oxidized VSCEL having a gallium phosphide (GaP) barrier layer according to the present invention improves the light efficiency by 40% at the maximum by improving the electrode protection and current flow of 860nm VCSEL having an oxidized aperture, and can confirm the efficiency optimization range between the applicable high-conductivity substance and the oxidized aperture of the VCSEL.
According to the present invention, there is provided a method that can improve the luminescence and light extraction of an oxidized VCSEL, which is reduced in emission efficiency due to a narrow emission region and an upper DBR.
Drawings
Fig. 1 is a cross-sectional view showing a conventional oxide VCSEL.
Fig. 2 (a) is a Scanning Electron Microscope (SEM) image showing a DBR damage pattern occurring when oxidation is performed, fig. 2 (b) shows a shape of a current window, a black band pattern is a trench (trench) region, a middle region is a columnar region emitting light, and a brighter portion is an oxidized portion.
Figure 3 is a cross-sectional view of an oxidized VCSEL according to an embodiment of the present invention.
Fig. 4 is a cross-sectional view of an oxidized VCSEL without a GaP layer of comparative example 1 in comparison with the present invention.
Fig. 5 is a cross-sectional view of an oxidized VCSEL having a non-rough surface type GaP layer of comparative example 2 in comparison with the present invention.
Fig. 6 is a diagram comparing the structure and upper surface of a rough surface type GaP layer as an example of the present invention, the state without GaP layer of comparative example 1, and the non-rough surface type GaP layer of comparative example 2.
Fig. 7 is a graph comparing the light intensity at a current of 20mA for the rough surface type GaP layer of the example of the present invention, the state without GaP layer of the comparative example 1, and the non-rough surface type GaP layer of the comparative example 2.
Fig. 8 is a graph comparing the rough surface type GaP layer of the example of the present invention, the GaP-free state of the comparative example 1, and the non-rough surface type GaP layer of the comparative example 2 in the current range of 0 to 50 mA.
Fig. 9 is a diagram illustrating a factor regarding light intensity generated in the VCSEL.
Fig. 10 is an explanatory view of light reflection of the rough surface type GaP layer as an example of the present invention, the state without GaP layer of comparative example 1, and the non-rough surface type GaP layer of comparative example 2.
Description of the reference numerals
100: oxidized VCSEL
110: lower electrode
120: substrate
130: lower DBR
140: active layer
150: upper DBR
160: GaP layer
170: upper electrode
180: oxide layer
Detailed Description
The present invention will be described in detail below with reference to examples. The following examples are merely illustrative, and the present invention is not limited thereto.
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