CN112928600A

CN112928600A - Semiconductor laser transmitter

Info

Publication number: CN112928600A
Application number: CN202110124370.6A
Authority: CN
Inventors: 雷述宇
Original assignee: Ningbo Abax Sensing Electronic Technology Co Ltd
Current assignee: Ningbo Abax Sensing Electronic Technology Co Ltd
Priority date: 2021-01-29
Filing date: 2021-01-29
Publication date: 2021-06-08

Abstract

The invention provides a semiconductor laser transmitter which is characterized by comprising a first DBR layer, a second DBR layer, a transparent conducting layer and a quantum well active region, wherein the transparent conducting layer is positioned above the first DBR layer, the quantum well active region is arranged between the first DBR layer and the second DBR layer, the first DBR layer is also connected with a substrate layer, and through the design, the VCSEL light beam quality is better, and the far-field divergence angle is further reduced; the conductivity and the light transmittance further improve the electro-optic conversion efficiency of the VCSEL and reduce the threshold current.

Description

Semiconductor laser transmitter

Technical Field

The invention relates to the technical field of lasers, in particular to a semiconductor laser transmitter.

Background

Semiconductor type lasers, which are very advantageous for the whole system because of their excellent controllability and easy realization of array type integrated design, are increasingly utilized to facilitate adjustment of laser parameters by controlling characteristics such as voltage during each probing process, and are also called semiconductor Laser Diodes (LDs), which are lasers developed in the 20 th century and the 60 th era. There are dozens of working substances of semiconductor laser, such as gallium arsenide (GaAs), cadmium sulfide (CdS), etc., and the excitation modes mainly include an electric injection type, an optical pump type, and a high-energy electron beam excitation type. The advantages of semiconductor lasers mainly include the following aspects: 1) small volume and light weight. 2) The stimuli can be injected: it can be driven with only a few volts injected into a current in the milliamp range. No other excitation devices and components than the power supply device are required. The electric power is directly converted into optical power, and the energy efficiency is high. 3) The wavelength range is wide: by appropriate selection of materials and alloy ratios, lasers of any wavelength can be realized over a wide range of wavelengths, both infrared and visible. 4) Can directly modulate: the oscillation intensity, frequency and phase can be modulated in the range of dc to ghz by superimposing the signal on the drive current. 5) The coherence is high: output light with high spatial coherence can be obtained with a single transverse mode laser. In Distributed Feedback (DFB) and Distributed Bragg Reflector (DBR) lasers, stable single longitudinal mode lasing, high temporal coherence, and the like are advantageous.

At present, a semiconductor laser which is more applied is a Surface Emitting semiconductor laser, and has many advantages compared with a traditional edge Emitting reported laser, and a Vertical-Cavity Surface Emitting laser VCSEL (Vertical-Cavity Surface-Emitting Lasers) in the Surface Emitting semiconductor laser has the advantages of high side mode rejection ratio, low threshold, small volume, easiness in integration, high output power and the like due to low threshold, circular light beams, easiness in coupling and easiness in two-dimensional integration. And the like, and become a hotspot for research in the field of photoelectrons. In the optical fiber communication system, a long wavelength vertical cavity surface emitting laser light source for dynamic single mode operation is an indispensable key element. The optical fiber is mainly used for medium-distance and long-distance high-speed data communication and optical interconnection, optical parallel processing and optical identification systems, and has important application in metropolitan area networks and wide area networks.

The basic structure of a VCSEL is shown in fig. 1, and includes an upper Distributed Bragg Reflector (DBR), a lower DBR), an oxide confinement hole, a multiple quantum well active region, and an ohmic contact electrode. The quantum well active region is located between the n-doped and p-doped DBRs. The DBR mirror has a reflectivity greater than 99% and is formed by alternating epitaxial growth of high and low index media or semiconductor materials, each layer of material having an optical thickness of 1/4 times the laser wavelength. The optical thickness of the active region is an integral multiple of the laser wavelength of 1/2 (or (2k +1) × 1/2), and photons which are injected into the active region by P-contact and generate stimulated radiation are reflected back and forth in the DBR and resonantly amplified, thereby forming laser light.

With the huge market demands and the gradually mature technology in the fields of automatic driving, consumer electronics and the like, the three-dimensional laser radar as a core system is a key factor for realizing the fields. The vertical cavity surface emitting laser is used for the emitting end light source of the current three-dimensional laser radar system and the three-dimensional optical sensing system, and in order to obtain better three-dimensional imaging resolution, the emitting end of the laser is required to have better light beam quality and divergence angle. The conventional VCSEL achieves a low far field divergence angle by reducing the diameter of the oxide confinement hole, but the continuous reduction of the aperture diameter of the oxide confinement layer increases the differential resistance, differential quantum efficiency of the VCSEL, thereby reducing the overall electro-optic conversion efficiency of the VCSEL. The prior art realizes the VCSEL with low divergence angle by changing the sheet structure of the VCSEL, including (1) a shallow relief method, but the method needs a specially designed epitaxial structure and precise etching depth control; (2) an obvious refractive index guide structure is not formed by a proton implantation technology, the mode characteristic and the beam characteristic of the proton implantation VCSEL are seriously dependent on a thermal lens effect, carrier reverse guide and a space hole burning effect, instability exists, and the dependence of beam quality on current is great; (3) the photonic crystal technology has the problems of large optical loss and resistance, complicated preparation process, requirement of accurately controlled transverse scale etching and deep etching and high requirement on equipment. The monolithic integrated microlens is an effective technical means for realizing a single mode by realizing VCSEL mode control on a VCSEL light-emitting window, and at present, a plurality of methods for preparing the VCSEL are provided, and mainly comprise a thermal reflux technology, laser direct writing, ICP/RIE etching, dielectric film sputtering and the like. The micro-lens integrated VCSEL does not need an additional external optical system in practical application, so that the complexity of the whole system is reduced and the integration level is improved.

Disclosure of Invention

The present invention is directed to a semiconductor laser emitter, which solves the problems of the related art, such as high complexity, low integration, low conductivity, and low light transmittance.

In order to achieve the above purpose, the embodiment of the present invention adopts the following technical solutions:

the embodiment of the invention provides a semiconductor laser transmitter, which is characterized by comprising:

a semiconductor laser transmitter, comprising:

the first DBR layer, the second DBR layer, the transparent conducting layer that is located first DBR layer top, and dispose in first DBR layer with quantum well active area between the second DBR layer, first DBR layer still connects the substrate layer.

Optionally, the transparent conductive layer is higher than the substrate layer.

Optionally, the micro lens is disposed above the transparent conductive layer.

Optionally, the thickness of the transparent conductive layer is 50-150 um.

Optionally, the transparent conductive layer penetrates through the substrate layer to reach the first DBR region.

Optionally, the aperture size of the transparent conductive layer is 10-200 um.

Optionally, the transparent conductive layer is higher than the substrate layer by 10um to 100 um.

Optionally, the micro lens is a curved surface, and the curvature radius of the micro lens is 20-150 um.

Optionally, the material of the microlens includes at least one of the following materials: photoresist, photosensitive resin and polyimide.

Optionally, the transparent conductive layer is made of zinc oxide.

The invention has the beneficial effects that: the invention provides a semiconductor laser transmitter which is characterized by comprising a first DBR layer, a second DBR layer, a transparent conducting layer and a quantum well active region, wherein the transparent conducting layer is positioned above the first DBR layer, the quantum well active region is arranged between the first DBR layer and the second DBR layer, the first DBR layer is also connected with a substrate layer, and through the design, the VCSEL light beam quality is better, and the far-field divergence angle is further reduced; the conductivity and the light transmittance further improve the electro-optic conversion efficiency of the VCSEL and reduce the threshold current.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

Fig. 1 is a schematic structural diagram of a laser transmitter provided in the prior art;

fig. 2 is a schematic structural diagram of a laser transmitter provided in the prior art;

fig. 3 is a schematic structural diagram of a laser transmitter according to an embodiment of the present invention;

fig. 4-8 are schematic diagrams of a process implementation provided by an embodiment of the invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention.

Fig. 1 is an exemplary view of a laser emitter disclosed In the prior art, which includes a first electrode 101, made of gold (Au), germanium (Ge), silver (Ag), palladium (Pd), platinum (Pt), nickel (Ni), titanium (Ti), vanadium (V), tungsten (W), chromium (Cr), aluminum (Al), copper (Cu), zinc (Zn), tin (Sn), and indium (In), and the like, and certainly not limited to a metal material, and may be a transparent electrode formed of a metal oxide or the like, and connected to a first DBR layer 102, wherein the first DBR layer 102 has a laminated structure In which low refractive index layers and high refractive index layers are alternately stacked. The low refractive index layer is, for example, p-type AlX1Ga (1-X1) As (0 < X1 < 1) having an optical film thickness of lambda/4 (or (2k +1) × lambda/4). The high refractive index layer is, for example, p-type AlX2Ga (1-X2) As (0 ≦ X2 < X1) with an optical film thickness of λ/4 (or (2k +1) × λ/4), which is also exemplified herein, and it is not particularly limited to the material that must be used, and it is sufficient that a bragg-type structure in which a medium-low refractive index and a high refractive index are alternately stacked is provided, 107 is an oxidation-limited layer, which serves to limit the generation of photons, to make the generated laser emission more centered, and at the same time, it can reduce the refractive index of the resonator to increase the light loss of the higher-order transverse mode in the position and thus suppress oscillation, in which the strongest intensity can be obtained, and further (2k +1) × λ/4) is providedA better focusing effect is achieved, and the specific material is not limited here either. 103 is an active region of the emitter, and the active region 103 has a quantum well structure in which a quantum well layer having an undoped al0.11as0.89gaas quantum well layer of 8nm thickness and barrier layers having an undoped al0.3ga0.7as layer of 5nm thickness are alternately stacked. For example, the active region 103 is designed to have light emission with a wavelength of 780nm, the optical thickness of the active region 103 is an integral multiple of the wavelength of 1/2 laser light, and photons which inject current into the active region through the P-contact first electrode 301 and generate stimulated radiation are reflected back and forth in the DBR and resonantly amplified, thereby forming laser light. The isolation layer formed of the undoped al0.6ga0.4as layer as a layer for forming the active region 3 includes a quantum well structure at the center thereof. The whole isolation layer has the same film thickness as lambda/n_rIs as large as an integer multiple of where λ is the oscillation wavelength and n is_rWhich is a refractive index of a medium, is also exemplified herein and not limited to realizing characteristics of material, thickness, and outgoing light wavelength, etc., the other end of the active region 103 is connected to the second DBR layer 104 having a laminated structure in which low refractive index layers and high refractive index layers are alternately stacked. The low refractive index layer is, for example, n-type AlX3Ga (1-X3) As (0 < X3 < 1) having an optical film thickness of lambda/4 (or (2k +1) × lambda/4). λ represents the oscillation wavelength of the semiconductor laser 1. The high refractive index layer is, for example, n-type AlX4Ga (1-X4) As (0. ltoreq. X4 < X3) having an optical film thickness of lambda/4 (or (2k + 1). lambda/4). Similar to the structure of the first DBR layer 102, the specific material is not limited herein, and other materials may be used to form a bragg-type structure in which a low refractive index and a high refractive index are alternately stacked, so that the DBR reflective region having such an arrangement may have a reflectivity of more than 99%. The second DBR layer 104 may further be connected to a substrate layer 105, for example made of a gallium arsenide (GaAs) substrate layer 105. The substrate layer 105 is made of a material having high transparency to the stacked structure (more specifically, to light generated by the active layer 103). The substrate layer 105 may be made of indium phosphide (InP), gallium nitride (GaN), indium gallium nitride (InGaN), sapphire, silicon (Si), silicon carbide (SiC), etc., which are not limited to the materials listed herein, and further the substrate layer 105 is connected to a second electrode 106 which may be made of a material similar to that of the first electrode 101. Through the electrodeUnder pressure, the VCSEL can be excited to operate.

Fig. 2 is a schematic structural diagram of a laser transmitter provided in the prior art; Vertical-External-Cavity Surface-Emitting lasers (VECSEL) can be divided into two types according to driving modes, and an optically-pumped Vertical External-Cavity Surface Laser (OP-VECSEL) and an electrically-pumped Vertical External-Cavity Surface Laser (EP-VECSEL) are more compact and miniaturized compared with the OP-VECSEL electrically-pumped VECSEL; on the other hand, EP-VECSEL can directly convert electric energy into laser output by electric injection, with higher electro-optic conversion efficiency. As shown in fig. 2, the external cavity mirror of EP-VECSEL is integrated by off-chip integration of the VCSEL. The semiconductor device comprises an external cavity Reflector, an N-type ohmic contact electrode, a substrate, an N-type doped Distributed Bragg Reflector (DBR), a multi-quantum well active region, a protective material layer, a P-type doped DBR and an N-type ohmic contact electrode from top to bottom. The quantum well active region is located between the n-doped and p-doped DBRs. The DBR mirror has a reflectivity greater than 99% and is formed by alternating epitaxial growth of high and low index media or semiconductor materials, each layer of material having an optical thickness of 1/4 times the laser wavelength. The optical thickness of the active region is integral multiple of 1/2 laser wavelength, and photons which inject current into the active region through P-contact and generate stimulated radiation are reflected back and forth in the DBR and resonantly amplified, thereby forming laser. The external cavity mirror of the EP-VECSEL as shown in fig. 2 is not conducive to further integration and miniaturization of the light source by integrating it outside the VCSEL chip.

Fig. 3 is a schematic structural diagram of a laser emitter according to an embodiment of the present invention, which is similar to the functions and materials of the layers in fig. 2, and will not be described herein, the improvement of the present invention is that the first DBR layer 301 is further connected to a substrate layer 306, the transparent conductive layer 304 is connected to a microlens 305, the transparent conductive layer penetrates through the substrate layer 306 to reach the first DBR 306 region, the aperture size of the transparent conductive layer 304 is 10-200um, and the material of the transparent conductive layer can be made of indium tin oxide, indium or zinc oxide (IZO), and the thickness is 50-150 um. Compared with the substrate, the material of the transparent conducting layer has good ohmic conduction characteristic, the transparent conducting layer material is deposited after the original substrate is etched, the efficient injection of current carriers is guaranteed, the electro-optic conversion efficiency of the VCSEL can be further improved, and the threshold current is reduced. Compared with a GaAs substrate, the transparent conducting layer has higher light transmittance, and can effectively reduce the emergent loss and equivalently improve the electro-optic conversion efficiency after replacing GaAs. The material filling of the transparent conductive layer 304 is higher than the substrate 30610-100um, and the boundary tension thereof is limited to ensure that the microlens material is diffused to the periphery in the thermal reflow process, so as to avoid the mutual adhesion between the smaller pitch (different light-emitting points). The material of the microlens 305 includes photoresist, photosensitive resin polyimide, etc., and has a radius of curvature of 20-150 um. Because the micro lens is integrated, the VCSEL beam quality is better, and the far field divergence angle is further reduced.

Fig. 4-8 are schematic diagrams of a process implementation provided by an embodiment of the invention. Fig. 4 shows the preparation of VCSEL chips, which are typically composed of three parts, a top bragg reflector (P-DBR), a resonant cavity and a bottom N-DBR, where the DBR is typically composed of 20-40 pairs of thin films, the thickness of the resonant cavity is typically on the order of a few microns, and the DBR must have a high reflectivity (typically greater than 99%) in order to achieve lasing. The substrate, which is typically made of GaAs, is located at the bottom of the device, and the structure is shown in fig. 4. FIG. 5 is a VCSEL substrate light-emitting hole etching, as shown in FIG. 5, a light-emitting hole with an aperture size of 10-200um is etched on a GaAs substrate; fig. 6 is a deposition of a transparent conductive layer made of indium tin oxide (ito), indium oxide (in), or zinc oxide (IZO), which has a thickness of 50-150um higher than that of the substrate layer by 10-100 um. FIG. 7 is a schematic view of an inkjet printing process with on-demand organic solvent injection and heating reflow; the micro-lens material micro-droplets are controllably sprayed onto the transparent conducting layer by adopting an ink-jet printing preparation method, and the micro-lens is formed by heating and refluxing, so that the ink-jet printing process is efficient and direct, and has higher process compatibility. The material of the micro lens comprises photoresist, photosensitive resin, polyimide and the like, and the curvature radius is 20-150 um. Fig. 8 is a process of flip-chip bonding the VCSEL chip to the substrate to complete the fabrication process.

The technical scheme of the invention realizes the following technical advantages:

(1) the micro lens has a shaping and converging effect on emergent light, so that the VCSEL light beam quality is better, and the far field divergence angle is further reduced;

(2) compared with the substrate, the transparent conductive layer material has good conductivity and light transmittance, so that the electro-optic conversion efficiency of the VCSEL is further improved, and the threshold current is reduced;

(3) the transparent conducting layer material is filled higher than the substrate, and the boundary tension of the transparent conducting layer material is limited to ensure that the microlens material is diffused towards the periphery in the thermal reflow process, so that the mutual adhesion among smaller pitch is avoided, and the preparation density of the microlens can be improved.

It is noted that, in this document, relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application. It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures. The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A semiconductor laser transmitter, comprising:

2. The semiconductor laser transmitter of claim 1, wherein the transparent conductive layer is higher than the substrate layer.

3. The semiconductor laser transmitter of claim 1, wherein a microlens is disposed over the transparent conductive layer.

4. The semiconductor laser transmitter of claim 1, wherein the transparent conductive layer has a thickness of 50-150 um.

5. The semiconductor laser transmitter of claim 1, wherein the transparent conductive layer extends through the substrate layer to the first DBR region.

6. The semiconductor laser transmitter of claim 1, wherein the transparent conductive layer has an aperture size of 10-200 um.

7. The semiconductor laser transmitter of claim 1, wherein the transparent conductive layer is 10um-100um higher than the substrate layer.

8. The semiconductor laser transmitter of claim 3, wherein the microlens is a curved surface having a radius of curvature of 20-150 um.

9. The semiconductor laser transmitter of claim 3, wherein the material of the microlens comprises at least one of: photoresist, photosensitive resin and polyimide.

10. The semiconductor laser emitter of claim 1, wherein the material of the transparent conductive layer is zinc oxide.