A strained quantum well vertical cavity surface emitting laser and its preparation method and application

Abstract

This invention discloses a strained quantum well vertical-cavity surface-emitting laser, comprising a top reflector and a bottom reflector, with a top spacer (p-spacer) and a bottom spacer (n-spacer) between the top and bottom reflectors. A first active region and a second active region are disposed between the top and bottom spacers, and a tunneling junction is disposed between the first and second active regions. This invention employs a dual-active-region structure, designing a tunneling junction structure between the two active regions. This allows the injected carriers to undergo two optical gain cycles within the dual-active-region structure, thus multiplying the output optical power and improving the photoelectric conversion efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor lasers, in particular to a strained quantum well vertical cavity surface emitting laser and a preparation method and application thereof. Background Art

[0002] Vertical cavity surface emitting lasers have unique advantages such as small size, small divergence angle, high beam quality, low cost, and easy two-dimensional integration. In recent years, they have aroused widespread research interest in the field of semiconductor lasers and have also expanded rapidly in the application-end market, including: 3D facial recognition, laser medical beauty, gas detection, smart home, lidar and other applications.

[0003] The single longitudinal mode operation and low divergence angle of vertical cavity surface emitting lasers make them have great potential application value in the field of gas sensing, among which oxygen detection is particularly important in the fields of biology, chemistry, industry, etc. The oxygen absorption line P9P9 is at 763.842nm. At present, vertical cavity surface emitting lasers in the 760nm band still have problems such as low emission power. Existing technical means often increase the output light power by increasing the device emission aperture, but the larger device aperture will cause multi-transverse mode transmission and increase the far-field divergence angle. Gas detection requires a single-mode laser light source, so the selection of large aperture devices to increase the output light power is very unfavorable for the application of gas detection; on the other hand, the method of using array structure design to achieve high-power output is relatively complicated, and it is necessary to consider the channel distance between adjacent single devices, the array filling factor and the uniformity of the epitaxial wafer, which will put higher requirements on the device structure and epitaxial growth.

[0004] Therefore, high power density, high conversion efficiency and low threshold are still the research focuses that urgently need to be broken through in the short-wavelength 760nm vertical cavity surface emitting laser currently used in oxygen sensors. Summary of the invention

[0005] In order to solve the defects in the prior art, the present invention provides a strained quantum well vertical cavity surface emitting laser and a preparation method and application thereof. The obtained vertical cavity surface emitting laser has improved emission power, increased photoelectric conversion efficiency and improved luminescence performance.

[0006] In order to achieve the technical purpose, the present invention adopts the following technical solutions:

[0007] The present invention first provides a strained quantum well vertical cavity surface emitting laser, comprising:

[0008] A top reflector and a bottom reflector, wherein a top space layer (p-spacer) and a bottom space layer (n-spacer) are provided between the top reflector and the bottom reflector, a first active region and a second active region are provided between the top space layer and the bottom space layer, and a tunnel junction is provided between the first active region and the second active region.

[0009] Preferably, the strained quantum well vertical cavity surface emitting laser is configured to emit laser light with a wavelength of 760 nm.

[0010] Preferably, the top reflector comprises a distributed Bragg reflector (DBR) stack, and the bottom reflector comprises a distributed Bragg reflector (DBR) stack.

[0011] More preferably, the top reflector distributed Bragg reflector (DBR) stack and the bottom reflector distributed Bragg reflector (DBR) stack both comprise alternating layers of high refractive index layers and low refractive index layers.

[0012] More preferably, the alternating layers are arranged in the following order: the starting layer from the middle toward the top reflector and the bottom reflector is a high refractive index layer, and the remaining layers are alternately arranged with the low refractive index layers.

[0013] More preferably, the number of alternating cycles is 20-40 cycles.

[0014] Preferably, the high refractive index layer is Al x Ga 1-x As, x ranges from 0.25 to 0.35.

[0015] Preferably, the low refractive index layer is Al x Ga 1-x As, x ranges from 0.85 to 0.95.

[0016] Preferably, the top space layer is: AlGaAs.

[0017] Preferably, the bottom space layer is: AlGaAs.

[0018] Preferably, both the first active region and the second active region include a multi-quantum well layer stack, and the multi-quantum well layer stack includes a series of quantum wells arranged between a series of barrier layers.

[0019] More preferably, the multi-quantum well layer stacking is as follows: both side boundaries of the first active region and the second active region are barrier layers, and the internal quantum well layers alternate with them in sequence.

[0020] More preferably, the number of quantum well layers is 3.

[0021] More preferably, the material of the quantum well layer is In x Ga (1-x-y) Al y As.

[0022] More preferably, the value range of x is 0.01-0.2, and the value range of y is 0.11-0.23.

[0023] More preferably, the thickness of the quantum well layer is 6-15 nm.

[0024] More preferably, the material of the barrier layer is AlGaAs.

[0025] More preferably, the barrier layer has a thickness of 8-15 nm.

[0026] Preferably, the first active region and the second active region are connected in series via the tunnel junction.

[0027] Preferably, the tunnel junction is a heavily doped PN junction, including a P layer and an N layer, the thickness of the P layer and the N layer are both 10 to 30 nm, including a P layer and an N layer, the thickness of the P layer and the N layer are both 10 to 30 nm, the tunnel junction is a homojunction or a heterojunction, and the material of the P layer and the N layer is selected from one or more wide bandgap and narrow bandgap materials such as GaAs, GaN, GaSb, InP, AlGaN, AlGaAs, InGaN, InGaAs, AlInGaAs, AlInGaN, AlGaAsSb, etc.

[0028] More preferably, the doping concentration of the P layer is in the range of 1 to 5×10 20 cm -3 The doping concentration of the N layer is in the range of 1 to 5×10 19 cm -3 .

[0029] More preferably, the tunnel junction includes an AlGaAs homojunction and a type II AlGaAs / AlGaAsSb heterojunction.

[0030] The present invention also provides a method for preparing the strained quantum well vertical cavity surface emitting laser, comprising the following steps:

[0031] The bottom reflector is obtained by MOCVD / MBE method, and then the bottom space layer, the first active area, the tunnel junction, the second active area, the top space layer are grown in sequence, and finally the top reflector is grown.

[0032] Preferably, the first active region and the second active region both contain three quantum well layers, and the order of growth from bottom to top is barrier layer, well layer, barrier layer, well layer, barrier layer, well layer, barrier layer; the tunnel junction grows a P-type heavily doped layer and an N-type heavily doped layer from bottom to top.

[0033] The present invention also provides an application of the strained quantum well vertical cavity surface emitting laser or the vertical cavity surface emitting laser obtained by the preparation method in an oxygen sensor.

[0034] The beneficial effects of the present invention are:

[0035] 1. The vertical cavity surface emitting laser structure of the present invention adopts a dual active area structure, introduces strain to increase gain, reduces laser threshold and absorption between valence bands, and combines the tunnel junction structure design at the same time, so that the injected carriers undergo optical gain twice in the dual active areas, thereby doubling the output light power, and the photoelectric conversion efficiency is also improved accordingly, reducing the device resistance, increasing the probability of carrier tunneling, and effectively reducing the light absorption and thermal effect of the device, thereby realizing a 760nm high-performance dual-junction vertical cavity surface emitting laser to solve the problems of low output power and low efficiency in the prior art.

[0036] 2. The present invention introduces a small amount of In component in the quantum well layer to introduce strain in the active area, reduce the threshold current of the device, effectively reduce the effective mass of holes, improve the mobility of carriers, and make the state density of the conduction band and the valence band equal, thereby reducing the threshold current at which the semiconductor laser starts stimulated radiation. The introduction of strained quantum wells reduces the threshold carrier density, improves the gain and conversion efficiency to increase the output light power, and effectively improves the luminescence performance of the device. The inventor creatively discovered during the research process that, under the condition of a wavelength of 760nm, the performance of the present invention is significantly improved compared to the device of the traditional ternary compound. After calculation, the performance difference between different x values ​​and y values ​​is not much, and the values ​​within the given range can obtain better performance results.

[0037] 3. A tunnel junction is designed between the two active regions of the present invention to connect them in series. The use of a second type of heterogeneous tunnel junction increases the probability of carrier tunneling, so that the injected carriers undergo two optical gains in the dual active regions, further doubling the output light power, and the photoelectric conversion efficiency increases exponentially with the number of active regions.

[0038] 4. The vertical cavity surface emitting laser obtained by the present invention can effectively improve the electro-optical conversion efficiency, accuracy, and wavelength thermal stability of the device and system for oxygen sensor applications, while reducing the power consumption of the device and the concentration measurement line of the gas to be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic structural diagram of a vertical cavity surface emitting laser of the present invention;

[0040] Figure 2 It is a comparison diagram of LIV curves of Example 1 of the present invention and Comparative Example 1;

[0041] Figure 3 This is the LIV curve of comparative example 2 without adding a tunnel junction. DETAILED DESCRIPTION

[0042] In order to enable those skilled in the art to better understand the technical solution of the invention, the present invention is further described in detail below in conjunction with specific implementation methods.

[0043] The present invention will now be described more fully below with reference to the accompanying drawings, in which some but not all embodiments of the invention are shown. Indeed, the invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, which are provided so that this disclosure will satisfy applicable legal requirements. Like reference numerals refer to similar elements throughout. As used herein, terms such as "top", "bottom", "middle", "inner", "upper", "lower", etc. are used for purposes of explanation in the examples provided below to describe the relative positions of certain components or parts of components. Thus, as an example, the term "top space layer" may be used for a spacer layer (i.e., a spacer layer); however, depending on the orientation of the particular item being described, the current spreading layer may be located at the top or bottom.

[0044] The present invention provides a strained quantum well vertical cavity surface emitting laser and a preparation method and application thereof, wherein strain is introduced to increase gain, reduce laser threshold and inter-valence band absorption, and a tunneling junction structure design is combined to realize a 760nm high-performance double-junction vertical cavity surface emitting laser, so as to solve the problems of low output power and low efficiency in the prior art.

[0045] like Figure 1 As shown, the present invention first provides a strained quantum well vertical cavity surface emitting laser, comprising:

[0046] A top reflector 1 and a bottom reflector 2, wherein a top space layer (p-spacer) 3 and a bottom space layer (n-spacer) 4 are provided between the top reflector 1 and the bottom reflector 2, a first active region 5 and a second active region 6 are provided between the top space layer 3 and the bottom space layer 4, and a tunnel junction 7 is provided between the first active region 5 and the second active region 6.

[0047] The present invention adopts a dual active region structure and designs a tunnel junction structure between the two active regions, so that the injected carriers undergo two optical gains in the dual active regions, thereby doubling the output optical power and improving the photoelectric conversion efficiency.

[0048] Specifically, in the present invention, the strained quantum well vertical cavity surface emitting laser is configured to emit laser light with a wavelength of 760nm. The vertical cavity surface emitting lasers in the prior art are often used for laser light with a wavelength of 0.85μm and longer, while the present invention can realize a high-performance double-junction vertical cavity surface emitting laser with a wavelength of 760nm.

[0049] In the present invention, specifically, the top reflector 1 includes a distributed Bragg reflector stack, and the bottom reflector 2 includes a distributed Bragg reflector stack; further, the top reflector distributed Bragg reflector (p-DBR) stack and the bottom reflector distributed Bragg reflector (n-DBR) stack both include alternating layers of high refractive index layers and low refractive index layers, and the alternating period number of the alternating layers is Figure 1 It is only for schematic illustration. In the actual design process, any period can be selected. In the embodiment of the present invention, the number of periods is 20-40 periods. Specifically, in the embodiment of the present invention, the arrangement order of the alternating layers is as follows: the starting layer from the middle to the top reflector 1 is the first high refractive index layer 11 (that is, the layer closest to the middle is the first high refractive index layer 11), and the starting layer from the middle to the bottom reflector 2 is the second high refractive index layer 21 (that is, the layer closest to the middle is the second high refractive index layer 21), and the remaining layers are alternated with the low refractive index layers. In the embodiment of the present invention, the high refractive index layer is Al x Ga 1-x As, x ranges from 0.25 to 0.35; the low refractive index layer is Al x Ga 1-x As, x ranges from 0.85 to 0.95; their thicknesses are all λ / 4n, where n is the refractive index of the high / low refractive index layer, and λ is the emission wavelength.

[0050] In the present invention, the material of the top space layer 3 is AlGaAs; the material of the bottom space layer 4 is AlGaAs; and their thicknesses are both such that the cavity length is about 1λ.

[0051] In the present invention, the first active region 5 and the second active region 6 both include a multi-quantum well layer stack, and the multi-quantum well layer stack includes a series of quantum wells arranged between a series of barrier layers. In an embodiment of the present invention, the multi-quantum well layer stack is specifically: the two side boundaries of the first active region 5 and the second active region 6 are barrier layers, and the internal quantum well layers alternate with them in sequence (that is, the two side boundaries of the first active region 5 are the first barrier layer 51 and the second barrier layer 52, and the two side boundaries of the second active region 6 are the third barrier layer 61 and the fourth barrier layer 62, and the internal quantum well layers alternate with them in sequence). In an embodiment of the present invention, the first active region 5 and the second active region 6 are both composed of three quantum well layers; in an embodiment of the present invention, the material of the quantum well layer is In xGa (1-x-y) Al y As; the value range of x is 0.01-0.2, and the value range of y is 0.11-0.23. In the traditional III-V material system, such as AlGaAs / GaAs material, the effective mass of the hole is relatively large, which is about five times the effective mass of the electron. This causes the Fermi level of the hole to reach the top of the valence band more slowly than the Fermi level of the electron, and the state density of the conduction band is about five times the state density of the valence band. Both cannot reach the threshold carrier density at the same time. The present invention introduces a small amount of In components in the quantum well and introduces strain in the active region, which can effectively reduce the effective mass of the hole, improve the mobility of the carrier, and make the state density of the conduction band and the valence band equal, thereby reducing the threshold current at which the semiconductor laser starts stimulated radiation. The introduction of strained quantum wells reduces the threshold carrier density, improves the gain and conversion efficiency to increase the output light power, and the luminescence performance of the device is effectively improved. The inventor creatively discovered during the research process that, under the condition of being limited to a wavelength of 760nm, the performance of the present invention is significantly improved compared to the device of the traditional ternary compound. After calculation, the performance difference between different x values ​​and y values ​​is not much, and the values ​​within the given range can obtain good performance results; the thickness of the quantum well layer is 6 to 15nm; the material of the barrier layer is AlGaAs, and the thickness is 8 to 15nm.

[0052] The first active region 5 and the second active region 6 of the present invention are connected in series through the tunnel junction 7. In the embodiment of the present invention, the tunnel junction 7 is a heavily doped PN junction, including a P layer and an N layer, the thickness of the P layer and the N layer are both 10 to 30 nm, the tunnel junction is a homojunction or a heterojunction, and the materials of the P layer and the N layer are selected from one or more wide bandgap and narrow bandgap materials such as GaAs, GaN, GaSb, InP, AlGaN, AlGaAs, InGaN, InGaAs, AlInGaAs, AlInGaN, AlGaAsSb, etc.; further, the doping concentration of the P layer is in the range of 1 to 5×10 20 cm -3 The doping concentration of the N layer is in the range of 1 to 5×10 19 cm -3 ; Furthermore, the tunnel junction includes an AlGaAs homojunction and a type II AlGaAs / AlGaAsSb heterojunction. Aiming at the problem of low output power of a single device, the present invention adopts a dual active region structure (i.e., the first active region 5 plus the second active region 6 of the present invention), a tunnel junction structure is designed between the two active regions to connect them in series, and the type II tunnel junction increases the probability of carrier tunneling, so that the injected carriers undergo two optical gains in the dual active regions, thereby doubling the output optical power, and the photoelectric conversion efficiency increases doubly with the number of active regions.

[0053] The strained quantum well vertical cavity surface emitting laser of the present invention further comprises a substrate layer 8, wherein the substrate is GaAs and has a thickness of 400-500 nm.

[0054] The bottom reflector 1 in the strained quantum well vertical cavity surface emitting laser of the present invention also includes an oxide layer 13, which is located at a node close to the middle active region and is conventionally arranged in the art to limit the current in the middle region.

[0055] The present invention also provides a method for preparing the vertical cavity surface emitting laser, comprising the following steps: obtaining a bottom reflector by using a MOCVD / MBE method, then sequentially growing a bottom space layer, a first active region, a tunnel junction, a second active region, a top space layer, and finally growing a top reflector.

[0056] The present invention also provides an application of the vertical cavity surface emitting laser or the vertical cavity surface emitting laser obtained by the preparation method in an oxygen sensor. The application in the oxygen sensor requires the laser to be in the 760nm band. If the emission power is small, it will affect the test accuracy of the oxygen sensor. The vertical cavity surface emitting laser obtained by the present invention can effectively improve the electro-optical conversion efficiency, accuracy, and wavelength thermal stability of the device and system for the application of oxygen sensors, while reducing the power consumption of the device and reducing the concentration measurement line of the gas to be measured.

[0057] The following embodiments are used as examples to further illustrate the technical effects of the present invention, but are not intended to limit the present invention:

[0058] Example 1

[0059] The structure of the strained quantum well vertical cavity surface emitting laser of this embodiment is as follows Figure 1 As shown:

[0060] A top reflector 1 and a bottom reflector 2, wherein a top space layer (p-spacer) 3 and a bottom space layer (n-spacer) 4 are provided between the top reflector 1 and the bottom reflector 2, a first active region 5 and a second active region 6 are provided between the top space layer 3 and the bottom space layer 4, and a tunnel junction 7 is provided between the first active region 5 and the second active region 6.

[0061] The top reflector 1 and the bottom reflector 2 are distributed Bragg reflector stacks with alternating high refractive index layers and low refractive index layers, and the material of the high refractive index layer is Al 0.3 Ga 0.7 As; the low refractive index layer material is Al 0.93 Ga 0.07 As, the alternating period in the top reflector 1 is 26 periods, and the alternating period in the bottom reflector 2 is 40 periods; the material of the top space layer 3 is Al 0.4Ga 0.6 As~Al 0.6 Ga 0.4 As gradient composition, the bottom space layer 4 material is Al 0.6 Ga 0.4 As~Al 0.4 Ga 0.6 As gradient component, thickness is 250nm; the first active region 5 and the second active region 6 are both potential barrier layers at the boundaries on both sides, and the internal quantum well layers are alternated with them in sequence, the number of quantum well layers in the two active regions is 3, and the materials of the first active region 5 and the second active region 6 are both In 0.09 Ga 0.75 Al 0.16 As, with a thickness of 8nm; tunnel junction 7 is an AlGaAs homojunction and a type II AlGaAs / AlGaAsSb heterojunction, the thickness of the AlGaAs homojunction and the AlGaAs / AlGaAsSb heterojunction are both 10nm, and the doping concentration of AlGaAs is 5x10 19 cm -3 The doping concentration of AlGaAsSb is 1x10 20 cm -3 ; The substrate layer 8 is GaAs and the oxide layer 13 is AlAs.

[0062] The preparation method of the strained quantum well vertical cavity surface emitting laser is as follows: on a GaAs substrate 8, a bottom reflector 2 (composed of a high refractive index layer 21 and a low refractive index layer 22 grown alternately), a bottom space layer 4, a second active region 6 (the order of growth from bottom to top is barrier layer 62, quantum well layer 64, barrier layer, quantum well layer, barrier layer, quantum well layer 63, barrier layer 61), a tunneling junction 7 (a P-type heavy layer 21 and a low refractive index layer 22 grown alternately) are grown in sequence by MOCVD / MBE method. doped layer, N-type heavily doped layer), a first active area 5 (the order of growth from bottom to top is barrier layer 52, quantum well layer 54, barrier layer, quantum well layer, barrier layer, quantum well layer 53, barrier layer 51), a top space layer 3, a top reflector 1 (composed of a high refractive index layer 11 and a low refractive index layer 12 grown alternately); the grown epitaxial wafer is etched to form a mesa, and a 20-30 nm thick oxide layer 13 is prepared on the side of the top reflector 1 close to the active area by wet oxidation.

[0063] Comparative Example 1

[0064] Same as Example 1, except that the materials of the first active region 5 and the second active region 6 are Ga 0.75 Al 0.16 As.

[0065] Comparative Example 2

[0066] The same as the first embodiment, except that the tunnel junction 7 is not added.

[0067] Effect test:

[0068] The emission wavelength was limited to around 760nm, and the performance of the vertical cavity surface emitting laser obtained in Example 1 and Comparative Example 1 was tested. Figure 2 , the performance of the vertical cavity surface emitting laser of comparative example 2 is tested, see Figure 3 :

[0069] Figure 2 In the figure, the dotted line is the LIV curve of Example 1 of the present invention, and the solid line is the LIV curve of the traditional well layer material AlGaAs of Comparative Example 1. It can be seen from the values ​​of power variation with current, voltage variation with current, conversion efficiency, etc. that at an emission wavelength of 760nm, the output power and conversion efficiency of the quaternary compound quantum well layer introducing the In component in the present application are higher than those of the traditional AlGaAs material.

[0070] Figure 3 is the LIV curve of comparative example 2 without tunnel junction, and Figure 2 Comparison with the data of Example 1 shows that the introduction of the tunnel junction structure can greatly improve the slope efficiency of the PI curve, the output light power and the conversion efficiency, and the performance of the present invention is significantly improved.

[0071] The above are only preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be regarded as limiting the present invention, and the protection scope of the present invention should be based on the scope defined by the claims. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A strained quantum well vertical cavity surface emitting laser, characterized in that: include: A top reflector and a bottom reflector, wherein the top reflector and the bottom reflector include a top space layer and a bottom space layer between them, a first active region and a second active region are disposed between the top space layer and the bottom space layer, and a tunnel junction is disposed between the first active region and the second active region; the vertical cavity surface emitting laser is configured to emit laser light with a wavelength of 760 nm; The first active region and the second active region both include a multi-quantum well layer stack, wherein the multi-quantum well layer stack includes a series of quantum well layers arranged between a series of barrier layers, and the material of the quantum well layer is In x Ga (1-x-y) Al y As, where the value range of x is 0.01~0.2, and the value range of y is 0.11~0.

23.

2. The strained quantum well vertical cavity surface emitting laser according to claim 1, characterized in that: The multi-quantum well layer stack is specifically as follows: both sides of the boundaries between the first active region and the second active region are barrier layers, and the internal quantum well layers alternate with them in sequence.

3. The strained quantum well vertical cavity surface emitting laser according to claim 1, characterized in that: The first active region and the second active region are connected in series via the tunnel junction.

4. The strained quantum well vertical cavity surface emitting laser according to claim 1, characterized in that: The tunnel junction is a heavily doped PN junction, including a P layer and an N layer, the thickness of the P layer and the N layer are both 10 to 30 nm, the tunnel junction is a homojunction or a heterojunction, and the materials of the P layer and the N layer are selected from one or more wide bandgap and narrow bandgap materials such as GaAs, GaN, GaSb, InP, AlGaN, AlGaAs, InGaN, InGaAs, AlInGaAs, AlInGaN, AlGaAsSb, etc.

5. A method for preparing the strained quantum well vertical cavity surface emitting laser according to claim 1, comprising the following steps: The bottom reflector is obtained by MOCVD / MBE method, and then the bottom space layer, the first active area, the tunnel junction, the second active area, the top space layer are grown in sequence, and finally the top reflector is grown.

6. Use of the strained quantum well vertical cavity surface emitting laser according to any one of claims 1 to 4 or the strained quantum well vertical cavity surface emitting laser obtained by the preparation method according to claim 5 in an oxygen sensor.

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