A vertical cavity surface emitting laser

Abstract

The application discloses a vertical cavity surface emitting laser, and relates to the technical field of semiconductor devices.The vertical cavity surface emitting laser comprises a substrate, a bottom electrode, a bottom reflector, a multi-quantum well layer, a top reflector and a top electrode which are arranged in layers; and the top reflector is provided with a current limiting layer, wherein the current limiting layer comprises a current limiting area and a plurality of current channels defined by the current limiting area; the plurality of current channels are arranged at intervals; the plurality of current channels have low resistance; and the top electrode is provided with a plurality of through holes corresponding to the plurality of current channels one by one.The vertical cavity surface emitting laser can balance the current density of the current channels, so that the light spot mode of the vertical cavity surface emitting laser tends to be a Gaussian mode.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor devices, in particular to a vertical cavity surface emitting laser. BACKGROUND

[0002] A vertical cavity surface emitting laser (VCSEL) is also known as a vertical resonant cavity surface emitting laser. Unlike an edge emitting laser, which is generally manufactured by a separate chip process and emits laser light from the edge, the VCSEL forms a resonant cavity through a Bragg reflector and emits light in a direction perpendicular to the surface of a semiconductor substrate. Compared with an edge emitting semiconductor laser, the VCSEL has no optical cavity surface damage and has the advantages of low threshold current, dynamic single-mode operation, small far-field divergence angle, near-circular light spot, light direction perpendicular to the substrate surface, high fiber coupling efficiency, easy integration of two-microarray, and the like. Therefore, the VCSEL has a wide range of applications in optical interconnection, optical communication, optical signal processing, WDM fiber communication, neural networks, computer chips, and the like. Applications based on the VCSEL, such as 3D face recognition, gesture recognition, iris recognition, driverless vehicles, laser radar, and the like, are research hotspots.

[0003] Generally, the VCSEL is composed of a substrate, an N-DBR, a multiple quantum well (MQW) active region, a current limiting layer, a P-DBR, and an ohmic contact layer. The N-DBR and the P-DBR mirror form an optical resonant cavity of the VCSEL, and the MQW active region is a carrier gain medium. The VCSEL laser is realized by continuous lasing through electrical pumping. In order to reduce the threshold current when the laser light is emitted, a current confinement structure is usually used, that is, an unoxidized region and an oxide confinement region are formed by limiting the oxidation layer. The unoxidized region serves as a light emitting hole and also as an aperture for current, so that the current can only pass through the light emitting hole. Due to the large aperture of the light emitting hole in the prior art, when the laser operates, the current density is highest at the outer edge of the light emitting hole due to the distribution of the current, resulting in uneven current density in the light emitting hole. The uneven current density affects the VCSEL light spot mode, and an ideal Gaussian mode cannot be obtained. SUMMARY

[0004] The present application aims to provide a vertical cavity surface emitting laser that can balance the current density of the current channel to make the light spot mode of the vertical cavity surface emitting laser tend to be a Gaussian mode.

[0005] The embodiment of the application provides a vertical cavity surface emitting laser, comprising a substrate, a bottom electrode, a bottom reflector, a multi-quantum well layer, a top reflector and a top electrode which are arranged in a stack, wherein the top reflector is provided with a current limiting layer, the current limiting layer comprises a current limiting region and a plurality of current channels defined by the current limiting region, the plurality of current channels are arranged in a spaced manner, the plurality of current channels have low resistance, and the top electrode is provided with a plurality of through holes in one-to-one correspondence with the plurality of current channels.

[0006] As an implementable manner, the projection of the plurality of current channels on the substrate corresponds to the projection of the plurality of through holes on the substrate.

[0007] As an implementable manner, the aperture of the current channel is smaller than the aperture of the corresponding through hole.

[0008] As an implementable manner, the bottom electrode comprises a bottom ohmic contact layer and a metal electrode connected and arranged on both sides of the bottom ohmic contact layer, the bottom ohmic contact layer is located between the substrate and the bottom reflector, the cross-sectional area of the bottom ohmic contact layer is larger than the cross-sectional area of the bottom reflector so that a first step is formed between the bottom reflector and the bottom ohmic contact layer, the outer periphery of the bottom ohmic contact layer is exposed, and the metal electrode is arranged on the upper surface of the exposed part of the bottom ohmic contact layer.

[0009] As an implementable manner, the cross-sectional area of the multi-quantum well layer is smaller than the cross-sectional area of the bottom reflector so that a second step is formed between the multi-quantum well and the bottom reflector, and the outer periphery of the bottom reflector is exposed.

[0010] As an implementable manner, the surface of the first step, the surface of the second step and the surface of the top reflector are provided with an anti-reflection layer.

[0011] As an implementable manner, the current limiting region is formed by ion implantation, or the top reflector is formed by secondary growth epitaxy deposition to form the current limiting layer in the top reflector.

[0012] As an implementable manner, the apertures of the plurality of current channels are the same and are arranged on the current limiting layer in a uniform manner.

[0013] As an implementable manner, the top reflector comprises a P-type distributed Bragg reflector, and the bottom reflector comprises an N-type distributed Bragg reflector.

[0014] As an implementable manner, the P-type distributed Bragg reflector comprises a stack of C-doped Al x Ga 1-X As / GaAs arranged alternately, and the N-type distributed Bragg reflector comprises Si-doped Al x Ga 1-XA stack formed by alternately arranging As and GaAs.

[0015] The beneficial effects of the embodiments of the present application include:

[0016] The vertical cavity surface emitting laser provided by the present application comprises a substrate, a bottom electrode, a bottom reflector, a multi-quantum well layer, a top reflector, and a top electrode, the top reflector is provided with a current limiting layer, when the vertical cavity surface emitting laser is working, the multi-quantum well layer forms a standing wave under the action of pumping, the top reflector and the bottom reflector have a reflectivity higher than 99% respectively, the standing wave is reflected back and forth between the oppositely arranged top reflector and bottom reflector, in the reflection process, the photon energy in the standing wave gradually increases to form lasing, and then the lasing is emitted through the through hole on the top electrode after passing through the current limiting layer. The current limiting layer comprises a current limiting area and a plurality of current channels defined by the current limiting area, the plurality of current channels are arranged at intervals, the plurality of current channels have low resistance, and the top electrode is provided with a plurality of through holes corresponding to the plurality of current channels, so that the current applied to the top electrode is applied to the multi-quantum well layer by the current channels, the material of the multi-quantum well layer is pumped to form a standing wave, and the plurality of current channels are arranged to make the current flow along the plurality of current channels, so as to balance the current density of the current channels, so that the spot mode of the vertical cavity surface emitting laser tends to be a Gaussian mode. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0018] Figure 1 Fig. 1 is a structural schematic diagram of a vertical cavity surface emitting laser provided by an embodiment of the present application;

[0019] Figure 2 Fig. 2 is another structural schematic diagram of a vertical cavity surface emitting laser provided by an embodiment of the present application.

[0020] Fig. 1 is a structural schematic diagram of a vertical cavity surface emitting laser provided by an embodiment of the present application; DETAILED DESCRIPTION

[0021] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some but not all of the embodiments of the present application. The components of the embodiments of the present application described and shown in the drawings can be arranged and designed in various different configurations.

[0022] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present application.

[0023] It should be noted that: similar reference numerals and letters represent similar items in the following drawings, therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0024] In the description of the present application, it should be noted that the orientation or positional relationship indicated by the terms "center", "vertical", "horizontal", "inner", "outer" and the like is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship commonly placed when the product of the present application is used, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third" and the like are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0025] In addition, the terms "horizontal", "vertical" and the like do not mean that the components must be absolutely horizontal or vertical, but can be slightly inclined. For example, "horizontal" only means that its direction is relatively more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined.

[0026] In the description of the present application, it should also be noted that, unless otherwise explicitly specified and limited, the terms "arrangement", "installation", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the communication inside two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0027] In order to reduce the threshold current when a vertical cavity surface emitter (VCSEL) is working, a current confinement structure is usually used. Specifically, a current confinement layer is set between the multi-quantum well layer and the top reflector. Some of the material in the current confinement layer is oxidized to form oxides with high resistance. The current will be conducted along the unoxidized part, thereby reducing the threshold current. In the prior art, the aperture of the unoxidized part is larger. Due to the current distribution, the current density is the highest at the outer edge of the emission aperture, resulting in uneven current density inside the emission aperture.

[0028] This application provides a vertical-cavity surface-emitting laser 100, such as Figure 1 , Figure 2 As shown, the substrate includes a substrate 110, a bottom electrode 120, a bottom reflector 130, a multi-quantum well layer 140, a top reflector 160, and a top electrode 170, all stacked together. A current confinement layer 150 is disposed in the top reflector 160. The current confinement layer 150 includes a current confinement region 152 and a plurality of current channels 151 defined by the current confinement region 152. The plurality of current channels 151 are spaced apart and have low resistance. The top electrode 170 is provided with a plurality of through holes 171 corresponding to the plurality of current channels 151.

[0029] The top electrode 170 is provided with through holes 171 corresponding to multiple current channels 151. The through holes 171 serve as the light outlet of the laser. A voltage is applied to the bottom electrode 120 and the top electrode 170 to form a current. The current is applied to the multi-quantum well layer 140 along the current channels 151 in the top reflector 160 and the current confinement layer 150, so that the multi-quantum well layer 140 forms a standing wave. The photons in the standing wave are reflected back and forth between the bottom reflector 130 and the top reflector 160. During the reflection process, the energy of the photons in the standing wave gradually increases to form a lasing, which then propagates along the current channels 151 and exits through the through holes 171.

[0030] The current confinement layer 150 can be made of AlGaAs material with a high aluminum content. Within the current confinement region 152, the high-aluminum AlGaAs material is oxidized to form Al2O3 material. Al2O3 has a high resistance, hindering the current flowing through it. The high-aluminum AlGaAs material has a low resistance, allowing for rapid current conduction. When current flows from the top electrode 170 through the top reflector 160 to the current confinement layer 150, the current can only flow through the unoxidized current channels 151. The arrangement of multiple current channels 151 allows current to flow through multiple channels, pumping the material within the multi-quantum well layer 140 to generate photons. The multiple current channels 151 disperse the current across them, achieving a balanced current density.

[0031] In addition, the forming manner of the current limiting layer 150 is not limited in the embodiments of the present application. For example, the current limiting region 152 in the AlGaAs with high aluminum component can be subjected to He ion implantation. Specifically, the high-speed moving He ions can destroy the crystal structure of the AlGaAs with high aluminum component, so that the Al ions in the AlGaAs with high aluminum component combine with oxygen ions to form an oxide.

[0032] The bottom reflector 130 and the top reflector 160 have very high reflectivity. In general, the reflectivity of the bottom reflector 130 and the top reflector 160 is greater than or equal to 99%.

[0033] The multi-quantum well layer 140 can include a plurality of quantum well structures arranged in a stack. The specific structure of each quantum well is not limited in the embodiments of the present application. For example, the stack can include GaAs layers and AlGaAs layers arranged alternately on the GaAs layers, or can include GaAs layers and GaInAs layers arranged alternately on the GaAs layers, or can include GaAs layers and AlGaInAs layers arranged alternately on the GaAs layers.

[0034] It should be noted that the current channel 151 in the embodiments of the present application is a channel through which current flows, and is also a channel through which the laser light exits. The plurality of through holes 171 are provided in the top electrode 170 one-to-one corresponding to the plurality of current channels 151, so as to form an exit window for the laser light on the top electrode 170.

[0035] It should be further noted that when the material of the current limiting layer 150 is the same as the material in the top reflector 160, the current limiting layer 150 can be arranged in one of the layers in the top reflector 160.

[0036] The vertical cavity surface emitting laser 100 provided in the application comprises a substrate 110, a bottom electrode 120, a bottom reflector 130, a multi-quantum well layer 140, a current limiting layer 150, a top reflector 160 and a top electrode 170 which are arranged in a stack. When the vertical cavity surface emitting laser 100 is in operation, the multi-quantum well layer 140 forms a standing wave under the action of pumping, the top reflector 160 and the bottom reflector 130 have a reflectivity higher than 99% respectively, the standing wave is reflected back and forth between the oppositely arranged top reflector 160 and bottom reflector 130, the photon energy in the standing wave gradually increases to form lasing in the process of reflection, and then the lasing is emitted through the through hole 171 on the top electrode 170 after passing through the current limiting layer 150. The current limiting layer 150 comprises a current limiting region 152 and a plurality of current channels 151 defined by the current limiting region 152, the plurality of current channels 151 are arranged at intervals, the plurality of current channels 151 have low resistance, the top electrode 170 is provided with a plurality of through holes 171 corresponding to the plurality of current channels 151 one by one, so that the current applied to the top electrode 170 is applied to the multi-quantum well layer 140 by the current channels 151 to pump the multi-quantum well layer 140 to form a standing wave, and the plurality of current channels 151 are arranged to make the current flow along the plurality of current channels 151, so as to balance the current density of the current channels 151 to make the spot mode of the vertical cavity surface emitting laser 100 tend to be Gaussian mode.

[0037] Optionally, as shown in Figure 1 The projection of the plurality of current channels 151 on the substrate 110 corresponds to the projection of the plurality of through holes 171 on the substrate 110 one by one.

[0038] The projection of the plurality of current channels 151 on the substrate 110 corresponds to the projection of the plurality of through holes 171 on the substrate 110 one by one. When the photon energy in the standing wave gradually increases to form lasing, the emission direction of the laser formed by lasing is usually perpendicular to the top reflector 160. When the projection of the plurality of current channels 151 on the substrate 110 corresponds to the projection of the plurality of through holes 171 on the substrate 110 one by one, the laser propagates along the extension direction of the current channel 151 to the through hole 171 and is emitted from the through hole 171, thereby improving the emission rate of the laser.

[0039] In an implementable manner of the embodiment of the application, as shown in Figure 1 The aperture of the current channel 151 is smaller than the aperture of the corresponding through hole 171.

[0040] When the multi-quantum well layer 140 forms a lasing light emitted from the top reflector 160, due to the presence of the current confinement region 152, the lasing light is emitted from the current channel 151, and since the lasing light has a divergence angle when emitted, the aperture of the through hole 171 is set to be larger than the aperture of the current channel 151, so that the lasing light parallel to the axial direction of the current channel 151 and the lasing light having a small angle with the axial direction of the current channel 151 can all be emitted from the through hole 171, thereby improving the light emission efficiency of the lasing light and improving the light emission efficiency of the vertical cavity surface emitting laser 100.

[0041] Optionally, the bottom electrode 120 comprises a bottom ohmic contact layer 121 and a metal electrode 122 connected to the bottom ohmic contact layer 121, the bottom ohmic contact layer 121 is located between the substrate 110 and the bottom reflector 130, the cross-sectional area of the bottom ohmic contact layer 121 is larger than the cross-sectional area of the bottom reflector 130 to form a first step between the bottom reflector 130 and the bottom ohmic contact layer 121, and the outer periphery of the bottom ohmic contact layer 121 is exposed, and the metal electrode 122 is arranged on the upper surface of the exposed part of the bottom ohmic contact layer 121.

[0042] The cross-sectional area of the bottom ohmic contact layer 121 is larger than the cross-sectional area of the bottom reflector 130 to form a first step between the bottom reflector 130 and the bottom ohmic contact layer 121, so that the current applied to the bottom ohmic contact can be reduced when flowing to the bottom reflector 130, thereby reducing the threshold current of the current.

[0043] In addition, the first step is formed between the bottom ohmic contact layer 121 and the bottom reflector 130, and the metal electrode 122 can be arranged on the step surface, so that the metal electrode 122 is directly in contact with the bottom ohmic contact layer 121, reducing the current path and thereby reducing the loss in the current flow process.

[0044] Those skilled in the art should know that in the production process of the vertical cavity surface emitting laser 100, a plurality of vertical cavity surface emitting lasers 100 are prepared on the same chip at one time, and then cutting is performed to form a single vertical cavity surface emitting laser 100. In order to avoid damage to the bottom ohmic contact layer 121 caused by stress during cutting, the cross-sectional area of the bottom ohmic contact layer 121 is smaller than the cross-sectional area of the substrate 110, so that the bottom ohmic contact layers 121 of adjacent two vertical cavity surface emitting lasers 100 are arranged in a spaced manner, leaving a cutting space, and when cutting to form a single vertical cavity surface emitting laser 100, only the cutting needs to be performed from the spacing.

[0045] In an implementable manner of an embodiment of the application, as Figure 1As shown, the cross-sectional area of the multi-quantum well layer 140 is smaller than that of the bottom reflector 130, so that a second step is formed between the multi-quantum well layer 140 and the bottom reflector 130, and the outer periphery of the bottom reflector 130 is exposed.

[0046] The cross-sectional area of the multi-quantum well layer 140 is smaller than that of the bottom reflector 130, so that a second step is formed between the multi-quantum well layer 140 and the bottom reflector 130, and the outer periphery of the bottom reflector 130 is exposed.

[0047] Optionally, as shown in FIG. 1C, the surface of the first step, the surface of the second step, and the surface of the top reflector 160 are provided with an anti-reflection layer 180. Figure 1 As shown, the surface of the first step, the surface of the second step, and the surface of the top reflector 160 are provided with an anti-reflection layer 180.

[0048] The surface of the first step, the surface of the second step, and the surface of the top reflector 160 are provided with an anti-reflection layer 180, which can avoid the reflection of the laser light propagating to the surface of the first step, the surface of the second step, and the surface of the top reflector 160, that is, all the laser light is emitted, thereby improving the emission rate of the laser light. The anti-reflection layer 180 on the surface of the top reflector 160 covers the through hole 171 on the top electrode 170.

[0049] In an implementable manner of the embodiment, the current limiting region is formed by ion implantation, or the top reflector is formed by secondary growth epitaxy deposition to form a current limiting region layer in the top reflector.

[0050] The current limiting region is formed by oxidizing the AlGaAs material with high aluminum component to form Al2O3 material, which has a large resistance and can hinder the current flowing thereto. Specifically, the AlGaAs material can be deposited first, and then the current limiting region 152 in the AlGaAs material with high aluminum component is subjected to He ion implantation. Specifically, the high-speed moving He ions are used to destroy the crystal structure of the AlGaAs material with high aluminum component, so that the Al ions in the AlGaAs material with high aluminum component combine with oxygen ions to form an oxide.

[0051] In addition, because the current limiting layer 150 is obtained by oxidizing a layer in the top reflector 160, and the top reflector 160 is provided in a stack, in the process of preparing the top reflector 160, a groove corresponding to the current limiting region can be formed by etching a layer of AlGaAs material in the top reflector 160, and then Al2O3 is deposited in the groove to form the current limiting region and form the current limiting layer, and then the remaining part of the top reflector 160 is prepared.

[0052] Optionally, as shown in FIG. 1C, the surface of the first step, the surface of the second step, and the surface of the top reflector 160 are provided with an anti-reflection layer 180. Figure 2As shown, multiple current channels 151 have the same aperture and are evenly distributed on the current limiting layer.

[0053] The multiple current channels 151 are configured with the same aperture, ensuring that the current flowing through them is uniform and preventing current unevenness caused by some current channels having larger apertures. Furthermore, the specific aperture value of the current channels 151 is not limited in this embodiment; those skilled in the art can set it according to the size of the vertical cavity surface-emitting laser and the required current density.

[0054] When multiple current channels 151 are evenly distributed on the current confinement layer, the current will be evenly distributed to the multiple current channels 151, thereby further balancing the current density of the current channels 151, so that the beam mode of the vertical cavity surface-emitting laser 100 tends to the Gaussian mode.

[0055] In one possible implementation of this application embodiment, the top reflector 160 includes a P-type distributed Bragg reflector, and the bottom reflector 130 includes an N-type distributed Bragg reflector.

[0056] When the top reflector 160 includes a P-type distributed Bragg emitter and the bottom reflector 130 includes an N-type distributed Bragg reflector, the types of charge carriers in the top reflector 160 and the bottom reflector 130 are different, which can prevent the recombination of charge carriers in areas where laser emission is not generated, thus avoiding energy loss.

[0057] Optionally, the P-type distributed Bragg reflector includes C-doped Al x Ga 1-X An N-type distributed Bragg reflector, consisting of Si-doped Al, is formed by alternating As / GaAs layers. x Ga 1-X Layers formed by alternating As / GaAs configurations.

[0058] Among them, Al x Ga 1-X As has a higher refractive index, while GaAs has a lower refractive index, resulting in a significant difference between the two, which improves the reflectivity of the distributed Bragg reflector. Specifically, the P-type distributed Bragg reflector in Al... x Ga 1-X In As / GaAs, C is doped into Al, and C enters Al. x Ga 1-X The As / GaAs lattice replaces the positions of Al atoms and Ga ions, creating vacancies at the original Al and Ga atom sites, thus forming a P-type distributed Bragg reflector. The N-type distributed Bragg reflector is configured similarly.

[0059] The above merely provides preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.

Claims

1. A vertical cavity surface emitting laser, characterized by, The current limiting layer includes a current limiting region and a plurality of current channels defined by the current limiting region, the plurality of current channels are arranged at intervals, and the plurality of current channels have low resistance. The projections of the plurality of current channels on the substrate correspond to the projections of the plurality of through holes on the substrate. The aperture of the current channel is smaller than the aperture of the corresponding through hole.

2. The vertical cavity surface emitting laser according to claim 1, characterized in that The bottom electrode includes a bottom ohmic contact layer and metal electrodes arranged on both sides of the bottom ohmic contact layer, the bottom ohmic contact layer is located between the substrate and the bottom reflector, the cross-sectional area of the bottom ohmic contact layer is larger than the cross-sectional area of the bottom reflector so that a first step is formed between the bottom reflector and the bottom ohmic contact layer, the outer periphery of the bottom ohmic contact layer is exposed, and the metal electrodes are arranged on the upper surfaces of the exposed portions of the bottom ohmic contact layer.

3. The vertical cavity surface emitting laser of claim 2, wherein, The cross-sectional area of the multi-quantum well layer is smaller than the cross-sectional area of the bottom reflector so that a second step is formed between the multi-quantum well and the bottom reflector, and the outer periphery of the bottom reflector is exposed.

4. The vertical cavity surface emitting laser according to claim 3, characterized in that The surfaces of the first step, the second step, and the top reflector are provided with an anti-reflection layer.

5. The vertical cavity surface emitting laser of claim 1, wherein, The current limiting region is formed by ion implantation, or the top reflector is formed by secondary growth epitaxial deposition to form a current limiting region in the top reflector.

6. The vertical cavity surface emitting laser of claim 1, wherein, The apertures of the plurality of current channels are the same and are arranged uniformly on the current limiting layer.

7. The vertical cavity surface emitting laser of claim 1, wherein, The top reflector includes a P-type distributed Bragg reflector, and the bottom reflector includes an N-type distributed Bragg reflector.

8. The vertical cavity surface emitting laser of claim 7, wherein, The P-type distributed Bragg reflector comprises C-doped Al x Ga 1-X As / GaAs alternately arranged to form a stack, the N-type distributed Bragg reflector comprising Si-doped Al x Ga 1-X As / GaAs alternately arranged to form a stack.

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