CN111969411A

CN111969411A - Semiconductor laser transmitter

Info

Publication number: CN111969411A
Application number: CN202010895476.1A
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: 2020-08-31
Filing date: 2020-08-31
Publication date: 2020-11-20

Abstract

The present invention provides a semiconductor laser transmitter, comprising: a first DBR layer, a second DBR layer, a quantum well active region disposed between the first DBR layer and the second DBR layer; a first electrode at least partially contained within the first DBR layer. The design that at least part of the first electrode is contained in the first DBR layer through the design of the structure reduces a P-type DBR heterojunction interface through which current flows, so that the series resistance of the DBRs can be reduced, and meanwhile, the current density in the center of the active region can be ensured.

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) in the Surface Emitting semiconductor laser has the advantages of high side mode rejection ratio, low threshold, small volume, easy integration, high output power and the like due to low threshold, circular light beam, easy coupling and easy two-dimensional integration, and becomes a hotspot of research in the photoelectron field. 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 integer multiple of the laser wavelength of 1/2 (or (2k +1) × 1/2) to satisfy the resonance condition.

Not only can a DBR mirror provide high reflectivity, doped to have conductivity that allows it to be the path for current flow, but the larger the difference in refractive index between the two semiconductor materials of the DBR, the fewer the number of pairs required to obtain high reflectivity. However, since the energy band of the semiconductor material and the refractive index of the material have an approximately linear relationship, the larger the difference in refractive index, the larger the band gap difference between the two materials, and thus the larger the discontinuity of the energy band at the interface of the homotype heterojunction formed by the two semiconductor materials, the higher the potential barrier at the interface of the heterojunction. These barriers create a larger resistance, which is more severe in a P-type DBR because holes have a larger effective mass. The larger resistance causes more joule heating to be generated from the device, which hinders high power output of the device. In order to reduce the resistance, it is necessary to eliminate the potential barrier at the heterojunction interface, improve the discontinuity of the energy band, and achieve the continuity of the conduction band or the valence band. The common method can use high doping near the interface or adopt a superlattice structure, and increase the tunnel effect to reduce the heterojunction barrier; the gradual change component can be adopted at the interface to flatten the energy band near the interface, so as to reduce the potential barrier, but the methods have the problems of complex process, high cost, poor reliability and the like, so that the development of a scheme which can eliminate the potential barrier at the heterojunction interface and has low reliability and high cost is an urgent problem to be solved.

Disclosure of Invention

The present invention is directed to provide a semiconductor laser emitter, which solves the problems of the related art, such as the high potential barriers at the interface of the heterojunction, which may form a large resistance, resulting in a large heat generation of the device, and the like, and even the whole laser emitter cannot be used.

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 first DBR layer, a second DBR layer, a quantum well active region disposed between the first DBR layer and the second DBR layer; a first electrode at least partially contained within the first DBR layer.

Optionally, the substrate layer is further included, and the substrate layer is connected with the second DBR layer.

Optionally, the first DBR layer and/or the second DBR layer is a semiconductor multilayer mirror structure, and the optical thickness of each DBR is (2k +1) times 1/4 wavelength, where k is a natural number.

Optionally, the first DBR layer is P-type doped, and the second DBR layer is N-type doped.

Optionally, a width of the electrode included in the first DBR layer at least one cross section is equal to or less than a width of the electrode not included in the first DBR layer.

Optionally, the interface between the substrate layer or the active region and the substrate is further connected with a second electrode.

Optionally, in at least one cross section of the laser emitter, the width of the first DBR layer is smaller than the width of the second DBR layer.

Optionally, a second electrode at least partially connected to the second DBR layer wider than the first DBR layer is further included.

Optionally, the depth of the first electrode contained in the first DBR layer is 1/4-3/4 of the thickness of the first DBR layer.

Optionally, an oxide confinement layer is further included between at least a portion of the first electrode included in the first DBR layer and the first DBR layer.

The invention has the beneficial effects that: the embodiment of the invention provides a semiconductor laser transmitter, which is characterized by comprising: a first DBR layer, a second DBR layer, a quantum well active region disposed between the first DBR layer and the second DBR layer; a first electrode at least partially contained within the first DBR layer. Since the energy band of the semiconductor material and the refractive index of the material have an approximately linear relationship, the larger the difference in refractive index, the larger the band gap difference between the two materials, and thus the larger the discontinuity of the energy band at the interface of homotype heterojunction formed by the two semiconductor materials, the higher the potential barrier at the interface of heterojunction. These barriers create a larger resistance, which is more severe in a P-type DBR because holes have a larger effective mass. The larger resistance causes more joule heating to be generated from the device, which hinders high power output of the device. In order to reduce the resistance, it is necessary to eliminate the potential barrier at the heterojunction interface, improve the discontinuity of the energy band, and achieve the continuity of the conduction band or the valence band. At least part of the first electrode is contained in the first DBR layer, so that a potential barrier at a heterojunction interface can be eliminated, the resistance is reduced, the device can avoid serious heating phenomenon in the using process, the reliability of the whole device in use is ensured, the precision and the service life of the device are ensured, and the like.

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 diagram of another prior art laser transmitter;

FIG. 3 is a schematic diagram of a structure of another laser transmitter provided in the prior art;

fig. 4 is a schematic structural diagram of a laser transmitter according to an embodiment of the present invention;

FIG. 5 is a schematic structural diagram of another laser transmitter according to an embodiment of the present invention;

fig. 6 is a schematic structural diagram of another laser transmitter according to an embodiment of the present invention;

fig. 7 is a schematic structural diagram of another laser transmitter according to an embodiment of the present invention;

fig. 8 is a schematic structural diagram of another laser transmitter according to an embodiment of the present invention;

fig. 9 is a schematic structural diagram of a first electrode according to an embodiment of the present 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 < X7) with an optical film thickness of λ/4 (or (2k +1) × λ/4), which is also exemplified herein, and a material for implementation is not specifically limited thereto, 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, and 107 is an oxidation-limited layer, which plays a role of limiting generation of photons, so that the generated laser emission is more centered, and at the same time, it can reduce the refractive index of the resonator to increase light loss of a higher-order transverse mode in the position and thus suppress oscillation, wherein the strongest intensity can be obtained in the higher-order transverse mode, thereby achieving a better collimation effect, and a specific material is not limited herein. 103a, 103b and 103c constitute 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 at a wavelength of 780nm, and the optical thickness of the active region 103 is an integral multiple of the wavelength of 1/2 laser light to satisfy the resonance condition. 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, but this is merely an exemplary illustration and does not limit the characteristics of the specific blanking and thickness, the wavelength of outgoing light, and the like. The whole isolation layer hasThe film thickness is the same as lambda/n_rIs as large as an integer multiple of where λ is the oscillation wavelength and n is_rIs a refractive index of the medium, and the other end of the active region 103 is connected to the second DBR layer 104, which 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, 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. The emitter of fig. 1 may emit laser light by electrode pressurization. Not only can the DBR mirror (comprising the first DBR layer 101 and the second DBR layer 104) provide high reflectivity, doped to be conductive to allow current flow, but the larger the difference in refractive index between the two semiconductor materials of the DBR, the fewer the number of pairs required to achieve high reflectivity. However, since the energy band of the semiconductor material and the refractive index of the material have an approximately linear relationship, the larger the difference in refractive index, the larger the band gap difference between the two materials, and thus the larger the discontinuity of the energy band at the interface of the homotype heterojunction formed by the two semiconductor materials, the higher the potential barrier at the interface of the heterojunction. These barriers create a larger resistance, which is more severe in a P-type DBR because holes have a larger effective mass. The larger resistance causes more joule heating to be generated from the device, which hinders high power output of the device. To reduce the resistance, it is necessary to eliminate the differenceThe potential barrier at the mass junction interface improves the discontinuity of the energy band and realizes the continuity of the conduction band or the valence band. The common method can use high doping near the interface or adopt a superlattice structure, and increase the tunnel effect to reduce the heterojunction barrier; the gradual change component can be adopted at the interface to enable the energy band near the interface to be flat, so that the potential barrier is reduced; a single intermediate component layer can be inserted between the high and low Al component layers to form a gradient component, so that the potential barrier can be reduced. To reduce the DBR series resistance, the electrode is also typically in direct contact with the active region, as shown in fig. 2 and 3, however, this structure reduces the current density at the center of the active region and increases the threshold current. As can be seen from the above analysis, in the prior art, a scheme for reducing or eliminating a potential barrier and further obtaining a lower resistance and a smaller heat generation amount is obtained, and there is a defect that a current density at the center of an active region is reduced and a threshold current is increased, which causes a problem that a device has a quality reliability life and the like in application.

Fig. 4 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. 1, and will not be described herein, the improvement of the present invention is that a first electrode 401 is at least partially included in a first DBR layer 402, where the first electrode can be etched out in the DBR layer by etching or the like, and then the first electrode is embedded therein, and the vertical electrode is located in the P-type DBR. Considering the current limiting effect of the oxide limiting hole 407, experiments and other ways can find that the depth of the first electrode included in the first DBR layer of the first electrode 401 is 1/4-3/4 of the thickness of the first DBR layer, and the optimal lowest position of the P-type vertical electrode should be higher than 1/4 times the height of the P-type DBR, so that the maximum reduction of the potential barrier and the limitation reliability of the oxide limiting hole 407 can be ensured.

Fig. 5 is a schematic structural diagram of another laser emitter according to an embodiment of the present invention, which is different from fig. 4 in that, in at least one cross section of the laser emitter, the width of the first DBR layer 502 is smaller than the width of the second DBR layer 504, so as to form a step shape, the second electrode 506 can be disposed at the step shape, so that the current threshold can be reduced by further reducing the potential barrier, and the voltage applied to the active region can be more easily and precisely controlled, so that the heat generation of the device is smaller.

Fig. 6 is a schematic structural diagram of another laser emitter according to an embodiment of the present invention, which is similar to the structure of fig. 5 and is provided with more steps and gradients, so that the first electrode can partially directly act on the active region, the potential barrier is further reduced on the premise of ensuring higher energy efficiency conversion, and the reliability and the life quality of the entire device are further improved.

Fig. 7 is a schematic structural diagram of another laser emitter according to an embodiment of the present invention, which is different from fig. 4 in that the side wall of the first electrode 701 embedded in the first DBR section 702 encounters more photons than the upper surface in consideration of the larger absorption rate of photons by metal, thereby affecting the light extraction efficiency of the VCSEL. While the lower surface of the first electrode 701 is located above the oxide confinement layer, which already confines the photons, the absorption of photons by the lower surface of the electrode is limited. The photon absorption by the first electrode 701 near the sidewalls of the active region should be limited primarily. After the grooves are etched, the sidewall near the center of the active region may be slightly oxidized to form an oxidation limiting layer 708, so as to reduce the absorption of photons by the metal, and the other structures are similar to the structure of fig. 4 and are not described herein again.

Fig. 8 is a schematic structural diagram of another laser emitter according to an embodiment of the present invention, in view of the modulation effect of the electrode on the light output, a portion of the vertical electrode may not coincide with a projection region of the surface electrode, as shown in fig. 8, the electrode may be a T-shaped structure, so that higher modulation efficiency is formed, and meanwhile, an etching structure with a larger size does not need to be disposed on the first DBR layer of the device, so as to ensure the reliability of the device, and in combination with the oxide confinement layer 808 on the sidewall, the device is ensured to reduce the DBR series resistance, and at the same time, the current density at the center of the active region is effectively ensured, the photoelectric conversion rate is improved, and the threshold current is reduced.

Fig. 9 is a schematic structural diagram of a first electrode according to an embodiment of the present invention, where the structure is an embodiment of the first electrode in fig. 8, and the structure is not limited to this structure.

The technical scheme of the invention realizes the following technical advantages: 1) the current density of the center of the active region can be effectively ensured while the series resistance of the DBR is reduced; 2) the photoelectric conversion rate is improved and the threshold current is reduced.

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, further comprising a substrate layer connecting the second DBR layer.

3. The semiconductor laser transmitter of claim 1, wherein the first DBR layer and/or the second DBR layer is a semiconductor multilayer mirror structure, and an optical thickness of each DBR is (2k +1) times 1/4 wavelength, where k is a natural number.

4. The semiconductor laser transmitter of claim 1, wherein the first DBR layer is P-type doped and the second DBR layer is N-type doped.

5. The semiconductor laser transmitter according to claim 1, wherein a width of the electrode included in the first DBR layer at least one cross section is equal to or less than a width of an electrode not included in the first DBR layer.

6. The semiconductor laser transmitter of claim 2, wherein the substrate layer or active region and substrate interface further connects a second electrode.

7. The semiconductor laser transmitter of claim 1, wherein the first DBR layer has a width that is less than the second DBR layer width in at least one cross-section of the laser transmitter.

8. The semiconductor laser transmitter of claim 7, further comprising a second electrode at least partially connected to the second DBR layer wider than the first DBR layer.

9. The semiconductor laser emitter of claim 1 wherein the first electrode included in the first DBR layer has a first electrode depth of 1/4-3/4 of the thickness of the first DBR layer.

10. The semiconductor laser emitter of claim 1 wherein an oxide confinement layer is further included between at least a portion of the first electrode included in the first DBR layer and the first DBR layer.