CN112310810A

CN112310810A - Semiconductor laser transmitter

Info

Publication number: CN112310810A
Application number: CN202011200779.3A
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: 2020-11-02
Filing date: 2020-11-02
Publication date: 2021-02-02

Abstract

The present invention provides a semiconductor laser, 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; the invention also comprises a light-emitting limiting hole with reduced parasitic capacitance characteristic, the oxidation limiting hole in the prior art is converted into the light-emitting limiting hole with reduced parasitic capacitance characteristic, for example, air, nitrogen and other gases are used as filling materials of the light-emitting limiting hole, so that compared with the oxidation limiting hole in the prior art, the dielectric constant of the material in the invention is only 1/4 of oxide, therefore, according to the calculation formula of parasitic capacitance, the parasitic capacitance of the oxidation limiting hole can be reduced to 1/4 under the same limiting hole size from the design of the bottom layer, and the invention is very useful for scene adaptation requiring high power and fast modulation rate in TOF laser ranging.

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. 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 light. The light source at the transmitting end of the three-dimensional laser radar system and the three-dimensional optical sensing system needs a high-power vertical cavity surface emitting laser, and the mainstream technology is realized by adopting the flight time technical direction no matter for the laser radar or the three-dimensional sensing, so that higher requirements are provided for the light source in the laser radar and the three-dimensional sensing system. Because the power and modulation rate of the VCSEL determine the measurement range and resolution of the lidar system, the modulation rate of the VCSEL is mainly determined by two factors, i.e. internal factors: determining a rate equation of interaction of electrons and photons in the VCSEL after the electrical injection; external factors: the external limiting factor is mainly the influence of the RC parasitic parameters of the device itself on the high frequency characteristics, and when the high-speed VCSEL is subjected to the electro-optical modulation, the devices are substantially consistent, so that the external RC electrical parasitic parameters need to be reduced to increase the modulation rate of the VCSEL.

The parasitic parameters of the whole VCSEL device can be divided into internal parasitic and external parasitic, and the external parasitic mainly comes from the parasitic introduced by the package of the VCSEL device and is the main means and way for reducing the parasitic. Then, when the external parasitic voltage is reduced to a certain value, the internal RC parasitic voltage becomes a factor that limits the performance improvement. The main sources of the internal parasitic capacitance of the VCSEL include three, namely, the capacitance between the upper and lower electrodes, the active region capacitance, and the oxidation limiting layer capacitance, wherein the oxidation limiting layer capacitance is the main capacitance contribution part in the VCSEL chip.

Therefore, it is an urgent technical problem to develop a method for reducing the internal parasitic capacitance of a semiconductor laser transmitter, especially the parasitic capacitance introduced by the oxide confinement layer in the prior art.

Disclosure of Invention

The present invention is directed to provide a semiconductor laser transmitter, so as to solve the technical problem in the related art that the parasitic capacitance is large due to the existence of the oxidation limiting layer, and the problem that the matching application in the laser radar is not possible is serious.

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; and the light-emitting limiting hole is used for reducing the parasitic capacitance characteristic.

Optionally, the filling material in the light-emitting limiting hole is air.

Optionally, the filling material in the light extraction limiting hole is air with a first vacuum degree.

Optionally, the first vacuum degree is not lower than 10^-5Pa。

Optionally, the periphery of the light exit limiting hole further includes a protective layer.

Optionally, the protective layer is an organic material protective layer.

Optionally, the protective layer is an inorganic material protective layer.

Optionally, the first DBR layer further includes a positive ion implantation portion.

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

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

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; and the light-emitting limiting hole is used for reducing the parasitic capacitance characteristic. The invention changes the oxidation limiting hole of the prior art into the light-emitting limiting hole with the characteristic of reducing the parasitic capacitance, for example, air, nitrogen and other gases are used as filling materials of the light-emitting limiting hole, so that compared with the oxidation limiting hole of the prior art, the dielectric constant of the material of the invention is only 1/4 of oxide, therefore, according to the calculation formula of the parasitic capacitance, the parasitic capacitance of the oxidation limiting hole can be reduced to 1/4 under the same limiting hole size from the design of the bottommost layer, and thus, the invention is very useful for the scene adaptation in TOF laser ranging requiring high power and fast modulation rate.

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 structural diagram of a laser transmitter according to an embodiment of the present invention;

FIG. 4 is a schematic structural diagram of another 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.

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 diagram of a laser transmitter disclosed in the prior art, which includes a first electrode 101, which may be 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), indium (In), and the like, although not limited to metal materials, and may be a transparent electrode formed of metal oxide or the like, the first electrode being connected to the 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 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 wavelengths of 780nm, 950nm, etc., and the optical thickness of the active region 103 is an integral multiple of the wavelength of 1/2 laser 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 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_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 has an optical film thickness of lambda/or4 (or (2k +1) × λ/4) n-type AlX3Ga (1-X3) As (0 < X3 < 1). 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. As mentioned above, the light-exiting hole is limited to be the oxide limiting layer, that is, the light-exiting is limited by oxidation, but there are three main sources of internal parasitic capacitance of the VCSEL, the capacitance between the upper and lower electrodes, the capacitance of the active region, and the capacitance of the oxide limiting layer, wherein the capacitance of the oxide limiting layer is the main capacitance contribution part inside the VCSEL chip. In the prior art, a step-type structure scheme shown in fig. 2 is generally adopted, so that the area of the whole oxidation limiting layer can be reduced, and the parasitic capacitance can be reduced to a certain extent by reducing the equivalent sectional area. However, in the step-type design, it is necessary to ensure the exit diameter of the light exit hole of the laser to be 10 μm, 20 μm, etc., and to ensure the minimum size of the mesa for ensuring the reliability of the applied voltage, it is necessary to ensure the equivalent diameter range of more than 35 μm, so that the step-type design is limited, so that the reduction of the parasitic capacitance is limited,the requirement for the fast response characteristic of the laser light emitting source in the increasingly rapid development of the technology cannot be obtained by the design because the parasitic capacitance cannot be pursued to be small at a glance and the reliability of the device is lost, so based on the above technical problem, the present invention is improved from the design of the lowest layer to achieve the effect of reducing the parasitic capacitance in the device.

Fig. 3 is a schematic structural diagram of a laser emitter according to an embodiment of the present invention, which is described here by taking a step-type emitter as an example, but it is needless to say that in actual implementation, the step-type emitter is not limited to the step-type structure of fig. 3, and an oxide confinement layer (107 or 207) in the prior art is replaced in fig. 3 to be a light-emitting confinement hole 308 for reducing parasitic capacitance characteristics, that is, the material in the confinement hole at this time is a gas, and from the perspective of dielectric constant, the following relationship exists between the dielectric parameter of the oxide before being changed and the dielectric parameter of the gas, for example, air:

ε_{oxide compound}＝4ε_{Air (a)}； (1)

Therefore, the parasitic capacitance relationship between the two is as follows:

through the calculation of the formula, under the same size, the parasitic capacitance can be reduced to 1/4 of the original same device only by changing the material of the oxidation limiting layer into the light-emitting limiting hole 308 with the characteristic of reducing the parasitic capacitance, namely, the material of the oxidation limiting layer is changed into 0.25 of the original parasitic capacitance, so that the design is carried out, the oxidation limiting layer occupying the main parasitic capacitance contribution force in the device is greatly reduced, on the other hand, because the induced stress of the oxide layer on the adjacent active layer is eliminated, the reliability of the light-emitting limiting hole 308 to the whole device is improved, and the device can form high power and high response speed and can also ensure the reliability of the device.

In order to realize the light-emitting limiting hole 308 with reduced parasitic capacitance characteristic in the structure of FIG. 3, the oxide layer region (high-aluminum components Al0.98Ga0.02As and Al As) of the invention is subjected to a side oxidation technique to form an oxidation limiting layer (Al)₂O₃) The current confined oxide layer is removed from the oxide relief structure by selective wet chemical etching, and the light confining aperture 308 is formed by such a process, which is also only an exemplary implementation, although other processes may be used to form the light confining aperture 308.

Fig. 4 is a schematic structural diagram of another laser emitter according to an embodiment of the present invention, which is different from fig. 3 in that a protection layer 409 is further included outside the light-exiting limiting hole in fig. 4, the protection layer 409 is mainly used to prevent the oxidation of the active region by the external air released by the etching of the oxidation limiting layer from causing a problem in the reliability of the VCSEL, and further, the protection material includes an organic material and an inorganic material, where the organic material includes BCB, polyimide, and the like, and the inorganic material includes silicon oxide, silicon nitride, and the like. The deposition process adopted by the invention is a CVD method, and the vacuum degree in the process is more than 10^-5pa to ensure that there is no oxygen residue in the air dielectric layer to cause oxidation of the later active region, so the design can make the oxygen content in the air sealed in the limiting hole smaller, so even if the laser works in high power state, the generated high temperature environment is difficult to oxidize the surface of the light-emitting limiting hole 408, so the effect of lower parasitic capacitance of the whole device is ensured, and the device is ensured not to generate variation of electrical parameter characteristics in the using process, certainly, the process can be performed in nitrogen environment, so the gas sealed in the light-emitting limiting hole 408 is nitrogen, and the surface of the light-emitting limiting hole 408 of the device is not oxidized at high temperature, so the using reliability of the device is ensured, and here is not specially limited.

FIG. 5 is a schematic structural diagram of another laser emitter according to an embodiment of the present invention, in which the optical confinement hole 508 of this embodiment is adopted, so that the carrier confinement effect and the absorption effect of the higher-order optical mode of the previously adopted oxide confinement layer are reduced, and in order to ensure this function of the device, a positive ion implantation portion 510 is further disposed in the first DBR layer, and Zn may be adopted²⁺、H⁺The injection part 510 is obtained by an isocationic injection method, which performs carrier confinement on the one hand and performs injection on the other handHigh-order optical mode field absorption is realized, single longitudinal mode output is realized, and the injection depth is 1/2-3/4 of the distance from the upper surface of the light-emitting limiting hole 508 to the surface of the device, so that the reliability of limiting action can be ensured on one hand, and the application effect of the electrode 501 cannot be influenced on the other hand.

Fig. 6 is a schematic structural diagram of another laser emitter according to an embodiment of the present invention, in this embodiment, a light-exiting limiting hole 608 is provided, a protection portion 609 is further provided at a periphery of the light-exiting limiting hole, and in order to solve a problem that carrier limitation may not be reliable due to cancellation of an oxidation limiting layer, a positive ion implantation portion 610 is further provided, so that high response speed output of a device is ensured and at the same time higher reliability is provided, and other portions with similar functions are not described in detail again.

Fig. 7 and fig. 8 are schematic structural diagrams of another laser emitter according to an embodiment of the present invention, where more steps are provided compared with the previous solutions, and positions of the first electrode and the second electrode are different, so that the implementation can ensure that voltages at two ends of an active region of a device are applied more accurately, and the enhanced photoelectric conversion efficiency can also adapt to the development trend of miniaturization and low power consumption of the device, and the remaining functions similar to those of the previous embodiments are not repeated in detail.

The technical scheme of the invention realizes the following technical advantages: 1) reducing the internal parasitic capacitance of the VCSEL; 2) the oxide layer is released to eliminate the stress of the oxide limiting layer on the active region, so that the reliability of the device is 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 filling material in the light exit limiting hole is air.

3. The semiconductor laser transmitter of claim 1, wherein the filling material in the light exit limiting hole is air with a certain degree of vacuum.

4. The semiconductor laser transmitter of claim 3, wherein the degree of vacuum is not less than 10^-5Pa。

5. The semiconductor laser transmitter of claim 2 or 3, wherein the periphery of the exit limiting aperture further comprises a protective layer.

6. The semiconductor laser emitter of claim 5, wherein the protective layer is an organic material protective layer.

7. The semiconductor laser transmitter of claim 5, wherein the protective layer is an inorganic material protective layer.

8. The semiconductor laser emitter of claim 1 wherein the first DBR layer further comprises a positive implant.

9. The semiconductor laser transmitter of claim 1, further comprising a substrate layer connecting the second DBR layer.

10. 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.