CN115441306A - A strained quantum well vertical cavity surface emitting laser and its preparation method and application - Google Patents

Abstract

The invention discloses a strained quantum well vertical cavity surface emitting laser, comprising: a top reflector and a bottom reflector, and a top space layer (p-spacer) and a bottom space layer (p-spacer) are included between the top reflector and the bottom reflector. n-spacer), a first active region and a second active region are arranged between the top spacer layer and the bottom spacer layer, and a tunnel junction is arranged between the first active region and the second active region . The present invention adopts a dual active region structure, and designs a tunnel junction structure in two active regions, so that the injected carriers can perform two optical gains in the dual active region, so the output optical power is doubled, The photoelectric conversion efficiency is also improved.

Description

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

technical field

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

Background technique

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 extensive research interest in the field of semiconductor lasers and are also rapidly expanding in the application market. , including: 3D facial recognition, laser medical beauty, gas detection, smart home, laser radar and other applications.

The characteristics of single longitudinal mode operation and low divergence angle of vertical cavity surface emitting laser make it 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 and so on. The oxygen absorption line P9P9 is at 763.842nm, and the current VCSELs in the 760nm band still have problems such as low emission power. Existing technical methods often increase the output optical power by increasing the device’s emission aperture, but a larger device aperture will cause multi-transverse mode transmission and increase the far-field divergence angle, and gas detection requires a single-mode lasing light source, so choose Large-aperture devices to increase the output optical power are very unfavorable to the application of gas detection; on the other hand, the way to achieve high-power output with array structure design is more complicated, and it is necessary to consider the channel distance between adjacent single devices, array fill factor and epitaxy. This will put forward higher requirements on the device structure and epitaxial growth.

Therefore, high power density, high conversion efficiency and low threshold are still the research focus of short-wavelength 760nm vertical cavity surface emitting lasers used in oxygen sensors.

Contents of the invention

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

For realizing described technical purpose, the present invention adopts following technical scheme:

The present invention firstly provides a strained quantum well vertical cavity surface emitting laser, comprising:

A top reflector and a bottom reflector, comprising a top space layer (p-spacer) and a bottom space layer (n-spacer) between the top reflector and the bottom reflector, and being arranged between the top space layer and the bottom space layer There is a first active area and a second active area, and a tunnel junction is arranged between the first active area and the second active area.

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

Advantageously, said top reflector comprises a distributed Bragg reflector (DBR) stack and said bottom reflector comprises a distributed Bragg reflector (DBR) stack.

More preferably, said top reflector distributed Bragg reflector (DBR) stack and said bottom reflector distributed Bragg reflector (DBR) stack each comprise alternating layers of high and low refractive index layers.

More preferably, the arrangement sequence of the alternating layers is: the initial layer from the middle toward the top reflector and the bottom reflector is a high-refractive-index layer, and the rest of the layers alternate with low-refractive-index layers.

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

Preferably, the high refractive index layer is AlxGa1 _{- xAs} , and x ranges from 0.25 to 0.35.

Preferably, the low refractive index layer is AlxGa1 _{- xAs} , and x ranges from 0.85 to 0.95.

Preferably, the head space layer is: AlGaAs.

Preferably, the bottom space layer is: AlGaAs.

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.

More preferably, the multi-quantum well layer stack specifically includes: the boundaries on both sides of the first active region and the second active region are barrier layers, and the internal quantum well layers alternate with them in sequence.

More preferably, the number of quantum well layers is three.

More preferably, the material of the quantum well layer is In _x Ga _{(1-xy) Aly} As.

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

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

More preferably, the material of the barrier layer is AlGaAs.

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

Preferably, the first active region and the second active region are connected in series through the tunnel junction.

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 10-30 nm, including the P layer and the N layer, and the P layer and the N layer The thickness of the N layer is 10-30nm, the tunnel junction is a homojunction or a heterojunction, and the materials of the P layer and N layer are selected from GaAs, GaN, GaSb, InP, AlGaN, AlGaAs, InGaN, InGaAs , AlInGaAs, AlInGaN, AlGaAsSb and other wide and narrow band gap materials or one or more.

More preferably, the doping concentration of the P layer ranges from 1 to 5×10 ²⁰ cm ^-3 , and the doping concentration of the N layer ranges from 1 to 5×10 ¹⁹ cm ^-3 .

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

The present invention also provides a preparation method of the strained quantum well vertical cavity surface emitting laser, comprising the following steps:

The bottom reflector is obtained by MOCVD/MBE, and then the bottom space layer, the first active region, the tunnel junction, the second active region, the top space layer are grown sequentially, and finally the top reflector is grown.

Preferably, both the first active region and the second active region two comprise 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 , Potential barrier layer; The tunnel junction grows a P-type heavily doped layer and an N-type heavily doped layer sequentially from bottom to top.

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.

The beneficial effects of the present invention are:

1. The vertical cavity surface emitting laser structure of the present invention adopts a dual active region structure, and introduces strain to increase gain, reduce laser threshold and absorption between valence bands, and combine tunneling junction structure design at the same time, so that the injected carriers are in the dual The active region performs two optical gains in the middle, so the output optical power is doubled, and the photoelectric conversion efficiency is also improved, the device resistance is reduced, the carrier tunneling probability is increased, and the light absorption and thermal effects of the device are effectively reduced, realizing A 760nm high-performance dual-junction vertical-cavity surface-emitting laser was developed to solve the problems of low output power and low efficiency in the prior art.

2. The present invention introduces a small amount of In components into the quantum well layer to introduce strain in the active region, reducing the threshold current of the device, which can effectively reduce the effective mass of holes, improve the mobility of carriers, and make the conduction band and valence The density of states of the bands is equal, thereby reducing the threshold current for the semiconductor laser to start stimulated emission. The introduction of the strained quantum well reduces the threshold carrier density, improves the gain and conversion efficiency to increase the output optical power, and the luminous performance of the device be effectively improved. The inventor found creatively during the research process that, when the wavelength is limited to 760nm, compared with traditional ternary compound devices, the performance of the present invention is significantly improved. After calculation, the performance between different x values and y values The difference is not big, and the values in the given range can get better performance results.

3. A tunnel junction is designed for the two active regions of the present invention to connect them in series, and the second type of heterogeneous tunnel junction is used to increase the probability of carrier tunneling, so that the injected carriers are in the dual active regions. Two optical gains are performed to further double the output light power, and the photoelectric conversion efficiency doubles with the number of active regions.

4. The vertical cavity surface emitting laser obtained in the present invention can effectively improve the electro-optic conversion efficiency, accuracy, and wavelength thermal stability of the device and system for the application of oxygen sensors, and at the same time reduce the power consumption of the device and reduce the concentration measurement line of the gas to be measured. .

Description of drawings

Fig. 1 is a schematic structural view of a vertical cavity surface emitting laser of the present invention;

Fig. 2 is the LIV curve comparative figure of embodiment 1 of the present invention and comparative example 1;

FIG. 3 is a LIV curve of Comparative Example 2 without a tunnel junction.

detailed description

In order to enable those skilled in the art to better understand the technical solution of the invention, the present invention will be further described in detail below in conjunction with specific embodiments.

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown, which, in fact, can be embodied in many different forms and should not be construed as Being limited to the embodiments set forth herein, these embodiments are provided so that this disclosure will satisfy applicable legal requirements, like numerals referring to like elements throughout. As used herein, terms such as "top," "bottom," "middle," "inner," "upper," and "lower" in the examples provided below are used for explanatory purposes in order to describe certain components or parts of components. relative position. Thus, by way of example, the term "top spacer layer" may be used for a spacer layer (ie, a spacer layer); however, depending on the orientation of the particular item being described, the current spreading layer may be on top or on the bottom.

The invention provides a strained quantum well vertical cavity surface-emitting laser and its preparation method and application. Strain is introduced to increase gain, reduce laser threshold and absorption between valence bands, and combine tunneling junction structure design to achieve 760nm high performance. A double-junction vertical-cavity surface-emitting laser solves the problems of low output power and low efficiency in the prior art.

As shown in Figure 1, the present invention firstly provides a strained quantum well vertical cavity surface emitting laser, comprising:

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

The present invention adopts a dual active region structure, and designs a tunnel junction structure in two active regions, so that the injected carriers can perform two optical gains in the dual active region, so the output optical power is doubled, The photoelectric conversion efficiency is also improved.

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 suitable for laser light with a wavelength of 0.85 μm or longer. However, the present invention can realize a 760nm high-performance double-junction vertical cavity surface emitting laser.

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, for the number of alternating periods of alternating layers, Figure 1 is only for illustration To illustrate, in the actual design process, it can be any cycle. In the embodiment of the present invention, the number of cycles is 20-40 cycles; specifically, in the embodiment of the present invention, the arrangement order of the alternating layers is: The starting layer from the middle to the direction of 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 direction of 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 alternate with the low refractive index layer in turn. In an embodiment of the present invention, the high refractive index layer is Al _x Ga _1-x As, and x ranges from 0.25 to 0.35; the low refractive index layer is Al _x Ga _1-x As, and x ranges from 0.85 to 0.95 ; Its thickness is λ/4n, where n is the refractive index of the high/low refractive index layer, and λ is the outgoing wavelength.

In the present invention, the material of the head space layer 3 is AlGaAs; the material of the bottom space layer 4 is AlGaAs; the thickness thereof is such that the cavity length is about 1λ.

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 boundaries on both sides of the first active region 5 and the second active region 6 are barrier layers, and the inner quantum well layer and its Alternate (that is, the first barrier layer 51 and the second barrier layer 52 are located on both sides of the first active region 5, and the third barrier layer 61 and the fourth barrier layer are formed on both sides of the second active region 6. The barrier layer 62, the inner part is a quantum well layer alternately with it). In an embodiment of the present invention, both the first active region 5 and the second active region 6 are composed of three quantum well layers; in an embodiment of the present invention, the material of the quantum well layers is In _x Ga _{( 1-xy)} Al _y As; the value range of x is 0.01-0.2, and the value range of y is 0.11-0.23. The traditional III-V material system, such as the effective mass of holes in AlGaAs/GaAs materials, is relatively large , which is about five times the effective mass of its electron, which causes the Fermi level of the hole to reach the top of the valence band slower than the Fermi level of the electron, and the density of states in the conduction band is about the density of states in the valence band Five times, the two can not reach the threshold carrier density at the same time, the present invention introduces a small amount of In components in the quantum well to introduce strain in the active region, which can effectively reduce the effective mass of holes and improve the mobility of carriers , so that the density of states of the conduction band and the valence band are equal, thereby reducing the threshold current for the semiconductor to start the stimulated emission of the laser. The introduction of the strained quantum well reduces the threshold carrier density, improves the gain and conversion efficiency to increase the output light power, and the luminous performance of the device is effectively improved. The inventor found creatively during the research process that, when the wavelength is limited to 760nm, compared with traditional ternary compound devices, the performance of the present invention is significantly improved. After calculation, the performance between different x values and y values The difference is not large, and better performance results can be obtained for values within a given range; the thickness of the quantum well layer is 6-15nm; the material of the barrier layer is AlGaAs, and the thickness is 8-15nm.

According to the present invention, the first active region 5 and the second active region 6 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 10-30 nm, and the tunnel junction is a homogeneous Junction or heterojunction, the material of the P layer and N layer is selected from GaAs, GaN, GaSb, InP, AlGaN, AlGaAs, InGaN, InGaAs, AlInGaAs, AlInGaN, AlGaAsSb and other wide and narrow band gap materials one or more; further, the doping concentration of the P layer ranges from 1 to 5×10 ²⁰ cm ^-3 , and the doping concentration of the N layer ranges from 1 to 5×10 ¹⁹ cm ^-3 ; further, 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 (that is, the first active region 5 plus the second active region 6 of the present invention, two active region structures), two active regions A tunnel junction structure is designed to connect them in series. The second type of tunnel junction increases the probability of carrier tunneling, so that the injected carriers perform two optical gains in the dual active region, thus doubling the output optical power. The photoelectric conversion efficiency increases exponentially with the number of active regions.

The strained quantum well vertical cavity surface emitting laser of the present invention also includes a substrate layer 8, the substrate is GaAs with a thickness of 400-500nm.

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 near the direction of the middle active region. The current is in the middle area.

The present invention also provides the preparation method of the vertical cavity surface emitting laser, which includes the following steps: using MOCVD/MBE method to obtain the bottom reflector, and then sequentially growing the bottom space layer, the first active region, the tunnel junction, and the second active zone, headspace layer, and finally grow the top reflector.

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 on 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-optic conversion efficiency of the device and the system for the application of the oxygen sensor. , accuracy, wavelength thermal stability, while reducing device power consumption, reducing the concentration measurement line of the gas to be measured and other advantages.

The technical effect of the present invention is further described below with examples as examples, but not as a limitation of the present invention:

Example 1

The structure of the strained quantum well vertical cavity surface emitting laser of this embodiment is as shown in Figure 1:

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

Wherein, 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 The 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 _0.4 Ga _0.6 As～Al _0.6 Ga _0.4 Gradient composition of As, the material of the bottom space layer 4 is a graded composition of Al _0.6 Ga _0.4 As～Al _0.4 Ga _0.6 As, with a thickness of 250 nm; the first active region 5 and the second active region 6 The boundaries on both sides are barrier layers, and the internal quantum well layers alternate with them in turn. 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 In _0.09 Ga _0.75 Al _0.16 As, with a thickness of 8nm; the tunnel junction 7 is an AlGaAs homojunction and a second-type AlGaAs/AlGaAsSb heterojunction, the thickness of both the AlGaAs homojunction and the AlGaAs/AlGaAsSb heterojunction is 10nm, and the AlGaAs The doping concentration of AlGaAsSb is 5ⅹ10 ¹⁹ cm ^-3 , and the doping concentration of AlGaAsSb is 1ⅹ10 ²⁰ cm ^-3 ; the substrate layer 8 is GaAs, and the oxide layer 13 is AlAs.

The preparation method of the above-mentioned strained quantum well vertical cavity surface emitting laser: on the GaAs substrate 8, the bottom reflector 2 (composed of alternate growth of high refractive index layers 21 and low refractive index layers 22) is sequentially grown by MOCVD/MBE method, and the bottom space Layer 4, the 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), Tunneling junction 7 (P-type heavily doped layer and N-type heavily doped layer are grown sequentially from bottom to top), first active region 5 (the order of growth from bottom to top is barrier layer 52, quantum well layer 54, barrier layer , quantum well layer, potential barrier layer, quantum well layer 53, potential barrier layer 51), headspace layer 3, top reflector 1 (made up of high refractive index layer 11 and low refractive index layer 12 alternate growth); Will grow The epitaxial wafer is etched to form a mesa, and an oxide layer 13 with a thickness of 20-30 nm is prepared by wet oxidation on the side of the top reflector 1 close to the active area.

Comparative example 1

The same as the embodiment 1, the only difference is that the material of the first active region 5 and the second active region 6 is Ga _0.75 Al _0.16 As.

Comparative example 2

Same as the first embodiment, the only difference is that the tunnel junction 7 is not added.

Effect test:

The emission wavelength is limited to around 760nm, and the performance test is performed on the vertical cavity surface emitting laser obtained in Example 1 and Comparative Example 1, as shown in Figure 2, and the performance test is performed on the vertical cavity surface emitting laser of Comparative Example 2, as shown in Figure 3:

In Fig. 2, 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 such as the change of power with current, the change of voltage with current, and the conversion efficiency. Applying at the emission wavelength of 760nm, the output power and conversion efficiency of the quaternary compound quantum well layer introduced with In components are higher than those of traditional AlGaAs materials.

Figure 3 is the LIV curve of Comparative Example 2 without a tunneling junction, compared with the data of Example 1 in Figure 2, the introduction of the tunneling junction structure can greatly improve the slope efficiency of the P-I curve, the output light power and the conversion efficiency, The performance of the invention is obviously improved.

The above are only preferred implementations of the present invention. It should be noted that the above preferred implementations should not be regarded as limiting the present invention, and the scope of protection of the present invention should be based on the scope defined in the claims. For those skilled in the art, without departing from the spirit and scope of the present invention, some improvements and modifications can also be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims (10)

1. A strained quantum well vertical cavity surface emitting laser, characterized in that, comprising: A top reflector and a bottom reflector, including a top space layer and a bottom space layer between the top reflector and the bottom reflector, and a first active region and a second active region are arranged between the top space layer and the bottom space layer A source region, a tunnel junction is set between the first active region and the second active region. 2 . The strained quantum well vertical cavity surface emitting laser according to claim 1 , wherein the vertical cavity surface emitting laser is configured to emit laser light with a wavelength of 760 nm. 3 . 3. A kind of strained quantum well vertical cavity surface emitting laser according to claim 1, wherein the first active region and the second active region both comprise multi-quantum well layer stacks, and the multi-quantum well The layer stack includes a series of quantum well layers arranged between a series of barrier layers. 4. A strained quantum well vertical cavity surface emitting laser according to claim 3, wherein the multi-quantum well layer stack is specifically: both sides of the first active region and the second active region The boundaries are all potential barrier layers, and the internal quantum well layers alternate with them in sequence. 5. A strained quantum well vertical cavity surface emitting laser according to claim 4, characterized in that the material of the quantum well layer is In _x Ga _(1-xy) Al _y As. 6 . The strained quantum well vertical cavity surface emitting laser according to claim 5 , wherein the value range of x is 0.01-0.2, and the value range of y is 0.11-0.23. 7. A strained quantum well vertical cavity surface emitting laser according to claim 1, wherein the first active region and the second active region are connected in series through the tunnel junction. 8. A strained quantum well vertical cavity surface emitting laser according to claim 1, wherein the tunnel junction is a heavily doped PN junction, comprising a P layer and an N layer, and the P layer and the N layer The thickness of each layer is 10-30nm, the tunnel junction is a homojunction or a heterojunction, and the material of the P layer and N layer is selected from GaAs, GaN, GaSb, InP, AlGaN, AlGaAs, InGaN, InGaAs, One or more of AlInGaAs, AlInGaN, AlGaAsSb and other wide and narrow band gap materials. 9. A preparation method of the strained quantum well vertical cavity surface emitting laser as claimed in claim 1, comprising the following steps: obtain the bottom reflector with the MOCVD/MBE method, then grow the bottom space layer, the first active region, the tunnel Punch through the junction, the second active region, the head space layer, and finally grow the top reflector. 10. An application of the strained quantum well vertical cavity surface emitting laser according to any one of claims 1 to 8 or the strained quantum well vertical cavity surface emitting laser obtained by the preparation method of claim 9 on an oxygen sensor.

Images