A semiconductor laser and a method for manufacturing the same

Abstract

The invention provides a semiconductor laser and a preparation method thereof, wherein the semiconductor laser comprises a P-type GaN layer: the P-type GaN layer comprises a P-type AlGaN electron blocking layer, an unintentionally doped GaN layer and a high-temperature P-type GaN layer which are sequentially stacked from bottom to top; the P-type GaN layer is grown in a pure nitrogen atmosphere, which reduces the damage of hydrogen to the GaN layer at high temperature, and has a higher free hole concentration, which further improves the radiation recombination efficiency of electrons and holes; more importantly, the unintentionally doped GaN layer is inserted between the P-type AlGaN electron blocking layer and the high-temperature P-type GaN layer of the P-type GaN layer, which can cover the epitaxial defects extending from the bottom layer, and can also serve as a buffer layer, reduce lattice mismatch and thermal mismatch, and improve the overall crystal quality of the P-type GaN layer.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor process technology, and in particular to a semiconductor laser and a preparation method thereof. Background Art

[0002] In the manufacturing process of semiconductor lasers, the key part is the epitaxial growth of the P-type GaN layer. Among them, the P-type GaN layer epitaxial wafer is the key structural layer to realize the radiative recombination of electrons and holes in the light-emitting layer. As an acceptor atom, Mg is the only technically feasible P-type dopant at present. Mg forms Mg-H complex in the GaN layer in the form of deep energy level acceptors, resulting in conductive self-compensation of the P-type GaN layer. On the other hand, the free hole concentration of the P-type GaN layer is mainly affected by the growth conditions and annealing environment. However, the traditional P-type GaN growth process is to grow in a mixed atmosphere of nitrogen and hydrogen. Since the P-type GaN layer is more likely to form Mg-H complexes in the N2 / H2 atmosphere, the concentration of deep energy level acceptors as hole traps and non-radiative recombination centers is increased, making it impossible for the P-type GaN layer to obtain a higher free hole concentration, thereby reducing the luminous efficiency of the laser. In addition, hydrogen itself is dangerous, its control complexity is high, the control difficulty is large, and the high cost of hydrogen undoubtedly increases the cost of traditional processes. Summary of the invention

[0003] The present invention provides a semiconductor laser and a preparation method thereof, which are used to solve the defect in the prior art that the luminous efficiency of the semiconductor laser is reduced due to the low free hole concentration in the P-type GaN layer.

[0004] The present invention provides a semiconductor laser, which comprises a P-type GaN layer: the P-type GaN layer comprises a P-type AlGaN electron blocking layer, an unintentionally doped GaN layer and a high-temperature P-type GaN layer which are stacked in sequence from bottom to top; the P-type GaN layer is grown in a pure nitrogen atmosphere.

[0005] According to a semiconductor laser provided by the present invention, the thickness of the unintentionally doped GaN layer ranges from 20 nm to 100 nm.

[0006] According to a semiconductor laser provided by the present invention, the thickness of the P-type AlGaN electron blocking layer ranges from 50 nm to 150 nm.

[0007] According to a semiconductor laser provided by the present invention, the semiconductor laser comprises a substrate, a buffer layer, an unintentionally doped layer, an N-type GaN layer, a shallow well layer, a light-emitting layer, the P-type GaN layer and an annealing layer which are sequentially stacked from bottom to top;

[0008] Wherein, the shallow well layer includes a potential well layer and a potential barrier layer;

[0009] The P-type GaN layer includes a low-temperature P-type GaN layer, a P-type AIGaN electron blocking layer, an unintentionally doped GaN layer, a high-temperature P-type GaN layer and a P-type ohmic contact layer which are sequentially stacked from bottom to top.

[0010] According to a semiconductor laser provided by the present invention, the thickness of the P-type ohmic contact layer ranges from 3 nm to 150 nm.

[0011] According to a semiconductor laser provided by the present invention, the thickness of the buffer layer ranges from 2 nm to 8 nm.

[0012] The present invention also provides a method for preparing any of the semiconductor lasers described above, comprising:

[0013] Select a substrate;

[0014] growing an epitaxial layer on the substrate;

[0015] In a pure nitrogen atmosphere, growing a P-type GaN layer on the epitaxial layer;

[0016] The P-type GaN layer includes a P-type AlGaN electron blocking layer, an unintentionally doped GaN layer and a high-temperature P-type GaN layer which are sequentially grown from bottom to top.

[0017] According to the preparation method provided by the present invention, the nitrogen flow rate range when growing the P-type AlGaN electron blocking layer is 100 sccm to 300 sccm;

[0018] The nitrogen flow rate range when growing the unintentionally doped GaN layer is 150 sccm to 300 sccm;

[0019] The nitrogen flow rate range when growing the high temperature P-type GaN layer is 150 sccm to 350 sccm.

[0020] According to the preparation method provided by the present invention, growing a P-type GaN layer in a pure nitrogen atmosphere comprises: sequentially growing a low-temperature P-type GaN layer, a P-type AlGaN electron blocking layer, an unintentionally doped GaN layer, a high-temperature P-type GaN layer and a P-type ohmic contact layer on the epitaxial layer from bottom to top;

[0021] The nitrogen flow rate range when growing the low-temperature P-type GaN layer is 100 sccm to 300 sccm; the nitrogen flow rate range when growing the P-type ohmic contact layer is 150 sccm to 300 sccm.

[0022] According to the preparation method provided by the present invention, the step of growing an epitaxial layer on the substrate comprises:

[0023] growing a buffer layer having a thickness ranging from 2 nm to 8 nm on the substrate;

[0024] growing an unintentionally doped layer having a thickness ranging from 1 μm to 2 μm on the buffer layer;

[0025] An N-type GaN layer with a thickness ranging from 1.5 μm to 5.5 μm is grown on the unintentionally doped layer, wherein the N-type GaN layer is a highly Si-doped layer with a Si doping concentration ranging from 1×1018 cm -3 Up to 1019cm -3 ;

[0026] A shallow well layer is grown on the N-type GaN layer, wherein the shallow well layer includes a component of In X Ga 1-X N potential well layer and GaN barrier layer, where 0 <X<1;

[0027] A light emitting layer is grown on the shallow well layer, wherein the light emitting layer comprises an InGaN well layer and a GaN barrier layer that are alternately stacked and grown, wherein the thickness of the InGaN well layer ranges from 2nm to 4nm, and the thickness of the GaN barrier layer ranges from 5nm to 10nm.

[0028] According to the preparation method provided by the present invention, the method further comprises:

[0029] In a pure nitrogen atmosphere, a semiconductor laser having a P-type GaN layer is annealed to form an annealed layer on the P-type ohmic contact layer; wherein the annealing temperature is between 500° C. and 750° C., and the nitrogen flow rate ranges from 250 sccm to 400 sccm.

[0030] The present invention provides a semiconductor laser and a preparation method thereof, wherein the semiconductor laser comprises a P-type GaN layer: the P-type GaN layer comprises a P-type AlGaN electron blocking layer, an unintentionally doped GaN layer and a high-temperature P-type GaN layer which are stacked in sequence from bottom to top; the P-type GaN layer is grown in a pure nitrogen atmosphere, and compared with the conventional process in which the growth condition of the P-type GaN layer is a mixed gas of nitrogen and hydrogen, the damage of hydrogen to the GaN layer at high temperature is greatly reduced, and the semiconductor laser has a higher free hole concentration, which further improves the radiation recombination efficiency of electrons and holes, thereby enhancing the luminous efficiency of the semiconductor laser; more importantly, the unintentionally doped GaN layer is inserted between the P-type AlGaN electron blocking layer and the high-temperature P-type GaN layer of the P-type GaN layer, which can cover the epitaxial defects extending from the bottom layer of the epitaxial wafer, and the unintentionally doped GaN layer can also be used as a buffer layer to reduce lattice mismatch and thermal mismatch, improve the overall crystal quality of the P-type GaN layer, and further enhance the antistatic ability of the semiconductor laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 This is one of the structural schematic diagrams of a semiconductor laser provided by the present invention;

[0033] Figure 2 This is a comparison diagram of the luminous efficiency of semiconductor lasers obtained by different methods provided by the present invention;

[0034] Figure 3 This is the second structural schematic diagram of a semiconductor laser provided by the present invention;

[0035] Figure 4 This is the third structural schematic diagram of a semiconductor laser provided by the present invention;

[0036] Figure 5 It is a schematic flow chart of a method for preparing a semiconductor laser provided by the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] Embodiment 1

[0039] The P-type GaN layer is a key structural layer for achieving radiative recombination of electrons and holes in the light-emitting layer, in which Mg as an acceptor atom can form a Mg-H complex in the GaN layer in the form of a deep energy level acceptor. The traditional P-type GaN growth process is to grow in a mixed atmosphere of nitrogen and hydrogen. Since the P-type GaN layer is more likely to form a Mg-H complex in an N2 / H2 atmosphere, the deep energy level concentration that serves as a hole trap and non-radiative recombination center will be increased, causing the deep energy level acceptors to serve as hole traps and non-radiative recombination centers, making it impossible to obtain a high free hole concentration, thereby reducing the luminescence efficiency of the semiconductor laser.

[0040] To this end, the present invention provides a semiconductor laser. Figure 1 This is one of the structural schematic diagrams of a semiconductor laser provided by the present invention, such as Figure 1As shown, the semiconductor laser includes a P-type GaN layer 40; the P-type GaN layer 40 includes a P-type AlGaN electron blocking layer 42, an unintentionally doped GaN layer 43 and a high-temperature P-type GaN layer 44 stacked in sequence from bottom to top; the P-type GaN layer 40 is grown in a pure nitrogen atmosphere.

[0041] Compared with the traditional growth conditions of P-type GaN layer, which usually adopts a mixed gas of nitrogen and hydrogen as a carrier gas, in the embodiment of the present invention, the entire P-type GaN layer 40 is grown in a pure nitrogen atmosphere, which can greatly reduce the damage of hydrogen to the GaN layer at high temperature. Moreover, the P-type GaN epitaxial layer grown in a pure nitrogen atmosphere has a higher free hole concentration, which further accelerates the radiation recombination of electrons and holes to obtain a high internal quantum efficiency.

[0042] like Figure 2 As shown, a comparison is made between semiconductor lasers grown in pure N2 and N2 / H2 mixed gas at room temperature based on a current of 20 mA, and by comparing the normalized electroluminescence efficiencies of the two semiconductor lasers, it can be seen that the electroluminescence efficiency of the P-type GaN semiconductor laser structure grown with pure nitrogen carrier gas is increased by about 25% compared to the electroluminescence efficiency of the semiconductor laser grown under N2 / H2 mixed gas.

[0043] However, since the high-temperature P-type GaN layer 44 is a highly Mg-doped layer and is grown in a pure nitrogen atmosphere, the high-temperature P-type GaN layer 44 has no surface hydrogenation reaction in the absence of hydrogen, which may result in poor morphology on the crystal surface and the presence of large V-shaped pit openings. Therefore, an unintentionally doped GaN layer 43 is inserted between the P-type AlGaN electron blocking layer 42 and the high-temperature P-type GaN layer 44. On the one hand, the epitaxial defects extending from the bottom layer can be covered. On the other hand, the unintentionally doped GaN layer 43 can also serve as a buffer layer to reduce lattice mismatch and thermal mismatch, thereby improving the overall crystal quality of the P-type GaN layer and further enhancing the anti-static capability of the semiconductor laser.

[0044] Furthermore, if Figure 3 As shown, the P-type GaN layer 40 may also include a low-temperature P-type GaN layer 41, a P-type AlGaN electron blocking layer 42, an unintentionally doped GaN layer 43, a high-temperature P-type GaN layer 44 and a P-type ohmic contact layer 45 stacked in sequence from bottom to top.

[0045] The thickness of the low-temperature P-type GaN layer 41 ranges from 30 nm to 120 nm. For example, the thickness of the low-temperature P-type GaN layer 41 may be 110 nm.

[0046] Furthermore, considering that if the thickness of the P-type AlGaN electron blocking layer 42 is too thin, the blocking effect on electrons will be reduced, and if the thickness of the P-type AlGaN electron blocking layer 42 is too thick, the absorption of light by the layer will increase, reducing the light extraction efficiency of the semiconductor laser. Therefore, in order to ensure the electron blocking ability of the P-type AlGaN electron blocking layer 42 while improving the light extraction efficiency of the P-type GaN layer, the thickness range of the P-type AlGaN electron blocking layer 42 can be set to 50nm to 150nm; illustratively, the thickness of the P-type AlGaN electron blocking layer 42 is 80nm.

[0047] Further, the thickness of the unintentionally doped GaN layer 43 ranges from 20 nm to 100 nm. Exemplarily, the thickness of the unintentionally doped GaN layer 43 is 50 nm.

[0048] Further, the thickness of the high temperature P-type GaN layer 44 ranges from 50 nm to 150 nm. Exemplarily, the thickness of the high temperature P-type GaN layer 44 is 100 nm.

[0049] Furthermore, the thickness range of the P-type ohmic contact layer 45 can be set to be 3nm to 150nm. Considering that if the thickness of the P-type ohmic contact layer 45 is too thin, the contact between the epitaxial wafer and the chip electrode will be poor, and if the thickness of the P-type ohmic contact layer 45 is too thick, the luminous efficiency of the semiconductor laser will also be reduced. Therefore, in order to ensure good contact between the epitaxial wafer and the chip electrode and take into account the luminous efficiency of the semiconductor laser, the thickness of the P-type ohmic contact layer 45 can be 100nm.

[0050] In one embodiment, if Figure 4 As shown, the semiconductor laser may also include a substrate 10, a buffer layer 51, an unintentionally doped layer 52, an N-type GaN layer 20, a shallow well layer 60, a light emitting layer 30, the P-type GaN layer 40 and an annealing layer 70 which are sequentially stacked from bottom to top;

[0051] The shallow well layer 60 includes a potential well layer and a potential barrier layer.

[0052] Specifically, the substrate 10 may be a sapphire substrate, a silicon substrate or a silicon carbide substrate; the substrate 10 may also be a flat substrate or a patterned substrate.

[0053] The buffer layer 51 can be a low-temperature GaN layer, and its growth temperature can be controlled between 500°C and 700°C. The thickness of the buffer layer 51 will affect the quality of the epitaxial layer crystal and the luminous efficiency of the semiconductor laser. If the thickness of the buffer layer 51 is too thin, the quality of the epitaxial layer crystal grown on the buffer layer will be reduced, resulting in the generation of surface defects; if the thickness of the buffer layer 51 is too thick, the absorption of light by the layer will be enhanced, reducing the luminous efficiency of the semiconductor laser. Therefore, in order to take into account the quality of the semiconductor laser crystal while improving the luminous efficiency of the semiconductor laser as much as possible, the thickness range of the buffer layer 51 can be set between 2nm and 8nm; illustratively, the thickness of the buffer layer 51 can be 5nm.

[0054] In one embodiment, an unintentionally doped layer 52 is further included between the buffer layer 51 and the N-type GaN layer 20 . The unintentionally doped layer 52 is a transition layer between the buffer layer 51 and the N-type GaN layer 20 , and is used to further improve the crystal quality of the semiconductor laser.

[0055] In one embodiment, the unintentional doping layer can be a GaN layer. If the unintentional doping layer 52 is too thin, it will not only fail to function as a transition layer, but also reduce the crystal quality of the semiconductor laser and cause surface defects; if the unintentional doping layer 52 is too thick, it will increase the absorption of light by the unintentional doping layer 52 and reduce the luminous efficiency of the semiconductor laser; therefore, the thickness of the unintentional doping layer 52 can be set to between 1 μm and 2 μm; illustratively, the thickness of the unintentional doping layer 52 is 1.5 μm.

[0056] In one embodiment, the N-type GaN layer 20 is a highly Si-doped layer for providing electrons. The thickness of the N-type GaN layer 20 is 1.5 μm to 5.5 μm, and the Si doping concentration ranges from 1×10 18 cm -3 Up to 10 19 cm -3 .

[0057] In one embodiment, the shallow well layer 60 includes a composition of In X Ga 1-X N potential well layer 61 and GaN barrier layer 62, wherein 0 <X<1。

[0058] In one embodiment, the light emitting layer 30 includes alternately stacked InGaN well layers and GaN barrier layers, and alternately stacked InGaN well layers and GaN barrier layers can be obtained by alternately introducing different reaction materials into the reaction chamber. In order to improve the light emitting efficiency of the light emitting layer 30, the thickness of the InGaN well layer can be set in the range of 2nm to 4nm, and the thickness of the GaN barrier layer can be set in the range of 5nm to 10nm.

[0059] In one implementation manner, the semiconductor laser described in this embodiment further includes: an annealing layer 70 formed on the P-type ohmic contact layer 45; the growth condition of the annealing layer 70 is: annealing the semiconductor laser having the P-type GaN layer grown thereon in a pure nitrogen atmosphere.

[0060] In summary, a semiconductor laser provided by an embodiment of the present invention comprises a P-type GaN layer; the P-type GaN layer comprises a P-type AlGaN electron blocking layer, an unintentionally doped GaN layer and a high-temperature P-type GaN layer stacked in sequence from bottom to top; the P-type GaN layer is grown in a pure nitrogen atmosphere, which greatly reduces the damage of hydrogen to the P-type GaN layer at high temperature compared to the conventional process in which the growth condition of the P-type GaN layer is a mixed gas of nitrogen and hydrogen, and makes the P-type GaN layer have a higher free hole concentration, further improves the radiation recombination efficiency of electrons and holes, and thus enhances the luminous efficiency of the semiconductor laser;

[0061] More importantly, inserting an unintentionally doped GaN layer before the high-temperature P-type GaN layer can cover the epitaxial defects extending from the bottom layer of the epitaxial wafer. At the same time, the unintentionally doped GaN layer can also serve as a buffer layer to reduce lattice mismatch and thermal mismatch, improve the overall crystal quality of the P-type GaN layer, and further enhance the anti-static ability of the semiconductor laser.

[0062] Embodiment 2

[0063] The following is a description of a method for preparing a semiconductor laser provided by the present invention. The method for preparing the semiconductor laser described below and the semiconductor laser described above can be referred to in correspondence with each other.

[0064] Based on any of the above embodiments, Figure 5 It is a schematic diagram of the process of preparing a semiconductor laser. Figure 5 As shown, the method includes:

[0065] Step 110, selecting a substrate;

[0066] Step 120, growing an epitaxial layer on the substrate;

[0067] Step 130, growing a P-type GaN layer on the epitaxial layer in a pure nitrogen atmosphere;

[0068] The P-type GaN layer includes a P-type AlGaN electron blocking layer, an unintentionally doped GaN layer and a high-temperature P-type GaN layer which are sequentially grown from bottom to top.

[0069] Specifically, the first step is to select a substrate, which can be a sapphire substrate, a silicon substrate or a silicon carbide substrate; the substrate can also be a flat substrate or a patterned substrate. Subsequently, an epitaxial layer is grown on the selected substrate.

[0070] In some embodiments, the epitaxial layer includes a buffer layer, an unintentionally doped layer, an N-type GaN layer, a shallow well layer, and a light-emitting layer that are sequentially stacked and grown on the substrate from bottom to top.

[0071] In one embodiment, the method for preparing a semiconductor laser further includes: growing a buffer layer on a substrate; wherein the growth temperature of the buffer layer is 500°C-700°C and the thickness ranges from 2nm to 8nm. In actual application scenarios, if the thickness of the buffer layer is too thin, the quality of the epitaxial wafer crystal grown on the buffer layer will be reduced, resulting in the generation of surface defects; if the thickness of the buffer layer is too thick, it will cause the layer to absorb light, reducing the luminous efficiency of the semiconductor laser; therefore, the thickness of the buffer layer is preferably 5nm.

[0072] Furthermore, the buffer layer may be a low-temperature GaN layer.

[0073] In one embodiment, the method for preparing a semiconductor laser further includes: growing an unintentionally doped layer with a thickness of 1 μm to 2 μm on the buffer layer; the unintentionally doped layer serves as a transition layer between the buffer layer and the N-type GaN layer, which can further improve the crystal quality of the semiconductor laser.

[0074] Among them, if the thickness of the unintentional doping layer is too thin, it will not serve as a transition layer, and will also reduce the crystal quality of the semiconductor laser and cause surface defects; if the thickness of the unintentional doping layer is too thick, it will increase the absorption of light by the unintentional doping layer and reduce the luminous efficiency of the semiconductor laser; preferably, the thickness of the unintentional doping layer is 1.5μm.

[0075] Furthermore, the unintentionally doped layer may be an unintentionally doped GaN layer.

[0076] In one embodiment, the method for preparing a semiconductor laser further includes: growing an N-type GaN layer with a thickness ranging from 1.5 μm to 5.5 μm on the unintentionally doped layer; wherein the N-type GaN layer is a highly Si-doped layer, and the Si doping concentration ranges from 1×10 18 cm -3 Up to 10 19 cm -3 .

[0077] In one embodiment, the method for preparing a semiconductor laser further includes: growing a shallow well layer on the N-type GaN layer; wherein the shallow well layer includes a component of In X Ga 1-XN potential well layer and GaN barrier layer, where 0 <X<1。

[0078] In one embodiment, the method for preparing a semiconductor laser further includes: growing a light-emitting layer on the shallow well layer, the light-emitting layer including an InGaN well layer and a GaN barrier layer that are alternately stacked. The alternately stacked InGaN well layer and the GaN barrier layer can be obtained by alternately introducing different reaction materials into the reaction chamber. The thickness of the InGaN well layer ranges from 2nm to 4nm, and the thickness of the GaN barrier layer ranges from 5nm to 10nm. The light-emitting layer obtained in this way has a good luminous efficiency.

[0079] In one embodiment, the method for preparing a semiconductor laser may further include: growing a P-type GaN layer on the light-emitting layer.

[0080] Among them, compared with the traditional P-type GaN layer growth conditions of nitrogen and hydrogen as carrier gases, the P-type GaN layer in the embodiment of the present invention is grown in a pure nitrogen atmosphere, which greatly reduces the damage of hydrogen to the GaN layer at high temperature, and the P-type GaN epitaxial layer grown in a nitrogen atmosphere can have a higher free hole concentration, further improving the radiative recombination of electrons and holes to obtain a high internal quantum efficiency.

[0081] However, since the high-temperature P-type GaN layer is a highly Mg-doped layer and is grown in a pure nitrogen atmosphere, the lack of surface hydrogenation of the high-temperature P-type GaN layer may result in poor crystal surface morphology. Therefore, a layer of unintentionally doped GaN layer can be grown between the P-type AlGaN electron barrier and the high-temperature P-type GaN layer, which can not only cover the epitaxial defects extending from the bottom layer, but also serve as a buffer layer to reduce lattice mismatch and thermal mismatch, improve the crystal quality of the P-type GaN layer, and further enhance the antistatic capability of the semiconductor laser.

[0082] In one embodiment, during the growth of the P-type GaN layer, the nitrogen flow rate has a significant effect on the growth rate and crystal quality of the P-type GaN layer. At a low nitrogen flow rate, the growth rate will be slower and the crystal defects will increase; as the nitrogen flow rate increases, the growth rate of the P-type GaN layer will also increase accordingly; but too fast a gas flow rate may cause an uneven crystal surface and affect the quality of the epitaxial layer. Therefore, when growing a P-type GaN layer in a pure nitrogen atmosphere, the control of the nitrogen flow rate is key. The flow rate of nitrogen introduced into the reaction chamber for growing the P-type GaN layer is controlled in the range of 80sccm to 500sccm, and the corresponding temperature is controlled in the range of 700℃ to 1100℃. The thickness of the formed P-type GaN layer is 50nm to 500nm, and the hole concentration is 5.0×10 17 cm -3 ~1.0×10 20 cm -3 .

[0083] In some embodiments, the nitrogen flow rate range when growing the P-type AlGaN electron blocking layer is 100 sccm to 300 sccm; the nitrogen flow rate range when growing the unintentionally doped GaN layer is 150 sccm to 300 sccm; the nitrogen flow rate range when growing the high-temperature P-type GaN layer is 150 sccm to 350 sccm.

[0084] In other embodiments, in a pure nitrogen atmosphere, growing a P-type GaN layer may also include: growing a low-temperature P-type GaN layer, the P-type AlGaN electron blocking layer, the unintentionally doped GaN layer, the high-temperature P-type GaN layer and a P-type ohmic contact layer on the epitaxial layer in sequence from bottom to top; wherein, the nitrogen flow rate range when growing the low-temperature P-type GaN layer is 100 sccm to 300 sccm; the nitrogen flow rate range when growing the P-type ohmic contact layer is 150 sccm to 300 sccm.

[0085] Specifically, when growing a low-temperature P-type GaN layer, ammonia, ethylgallium, trimethylindium, trimethylaluminum and bismuthocene magnesium can be introduced into the reaction chamber for growing the low-temperature P-type GaN layer, the carrier gas is nitrogen, and the growth temperature of the low-temperature P-type GaN layer is 700° C. to 900° C. Since the growth temperature of the low-temperature P-type GaN layer is relatively low, the growth rate should not be too fast, otherwise the crystal quality will be poor, so the flow rate of nitrogen is easily controlled in a relatively low range, preferably the flow rate of nitrogen is controlled in a range of 100 sccm to 300 sccm.

[0086] In one embodiment, the growth thickness of the low-temperature P-type GaN layer is 30 nm to 120 nm. Exemplarily, the thickness of the low-temperature P-type GaN layer may be 110 nm.

[0087] When growing a P-type AlGaN electron blocking layer, ammonia, ethyl gallium, trimethyl indium and trimethyl aluminum can be introduced into the reaction chamber, the carrier gas is nitrogen, and the growth temperature of the P-type AlGaN electron blocking layer is 900°C to 1000°C. Since Al atoms and NH3 are prone to strong pre-reaction when the P-type AlGaN electron blocking layer grows, the nitrogen flow rate can be controlled within a suitably low range to avoid the parasitic reaction of Al atoms and NH3 caused by a large nitrogen flow rate. Preferably, the nitrogen flow rate can be controlled at 100 sccm to 300 sccm. In addition, considering that if the thickness of the P-type AlGaN electron blocking layer is too thin, the blocking effect on electrons will be reduced, and if the thickness of the P-type AlGaN electron blocking layer is too thick, the absorption of light by the layer will increase, reducing the light extraction efficiency, so the growth thickness of the P-type AlGaN electron blocking layer is 50nm to 150nm, and exemplarily, the thickness of the P-type AlGaN electron blocking layer is 80nm.

[0088] When growing an unintentionally doped GaN layer, ammonia and ethylgallium can be introduced into the reaction chamber where the unintentionally doped GaN layer is grown, the carrier gas is nitrogen, and the growth temperature is 950°C to 1100°C. Since the dislocations from the bottom layer and quantum well layer of the epitaxial wafer continue to extend to the P-type GaN layer, the opening of the V-shaped pit continues to expand to the P-type GaN layer, so when growing an unintentionally doped GaN layer, its growth rate can be increased so that it can quickly cover the defects extending to the P-type GaN layer. Here, the nitrogen flow rate can be increased relative to the low-temperature P-type GaN layer and the P-type AlGaN electron blocking layer, and the nitrogen flow rate can be optimized to be controlled at 150sccm to 300sccm. In addition, the growth thickness of the unintentionally doped GaN layer is 20nm to 100nm, and illustratively, the thickness of the unintentionally doped GaN layer is 50nm.

[0089] When growing a high-temperature P-type GaN layer, ammonia, ethylgallium and bismuth magnesium can be introduced into the reaction chamber, the carrier gas is nitrogen, and the growth temperature is 800°C to 1100°C. In order to improve the doping efficiency of Mg, a higher nitrogen atmosphere can be provided, so the nitrogen flow rate can be controlled at 150sccm to 350sccm. The growth thickness of the high-temperature P-type GaN layer is 50nm to 150nm. Exemplarily, the thickness of the high-temperature P-type GaN layer is 100nm.

[0090] When growing a P-type ohmic contact layer, ammonia, ethylgallium, trimethylindium, trimethylaluminum and bismuthocene magnesium can be introduced into the reaction chamber, the carrier gas is nitrogen, and the growth temperature is 750°C to 900°C. In a pure nitrogen atmosphere, the nitrogen flow rate has an important influence on the surface morphology and contact resistance of the P-type ohmic contact layer. A lower nitrogen flow rate will lead to a decrease in crystal quality, and a higher nitrogen flow rate will excessively increase the impurity concentration and resistivity. Therefore, the surface structure of the P-type ohmic contact layer can be made dense and defects and impurities can be reduced by optimizing the nitrogen flow rate.

[0091] Among them, the optimized nitrogen flow rate can be controlled at 150sccm to 300sccm. The growth thickness of the P-type ohmic contact layer can be 3nm to 150nm. Considering that if the thickness of the P-type ohmic contact layer is too thin, the contact between the epitaxial layer and the chip electrode will be poor, and if the thickness of the P-type ohmic contact layer is too thick, the luminous efficiency of the semiconductor laser will be reduced. Therefore, illustratively, the thickness of the P-type ohmic contact layer is 100nm.

[0092] The high growth temperature of the P-type GaN layer and the heat treatment after growth are extremely important. Therefore, after the P-type GaN layer is grown, the semiconductor laser can be annealed to form an annealing layer on the P-type ohmic contact layer. Among them, annealing can be performed in a pure nitrogen atmosphere, the annealing temperature is 500℃-750℃, and the nitrogen flow rate is 250sccm-400sccm. Compared with the annealing conditions of the traditional process using a mixed gas of nitrogen, hydrogen and ammonia (ratio 2:1:7), since the P-type GaN layer of the traditional process is grown using a mixed gas of N2 / H2, the surface has a higher temperature during the annealing process. In order to prevent the high-temperature decomposition of the surface GaN, ammonia needs to be continuously introduced to protect the surface of the epitaxial layer, which not only wastes the carrier gas raw material, but also causes the Mg acceptor to be unable to be activated due to incomplete annealing, thereby affecting the doping concentration of holes and reducing the recombination efficiency. Therefore, the new annealing process is performed on the semiconductor laser in a pure nitrogen atmosphere, and the further use of a pure nitrogen annealing process not only saves the carrier gas cost, but also makes the operation process simpler.

[0093] It can be seen that the preparation method provided by the embodiment of the present invention selects a substrate, grows an epitaxial layer on the substrate, and grows a P-type GaN layer on the epitaxial layer in a pure nitrogen atmosphere; wherein the P-type GaN layer includes a P-type AlGaN electron blocking layer, an unintentionally doped GaN layer and a high-temperature P-type GaN layer grown in sequence from bottom to top, which greatly reduces the damage of hydrogen to the GaN layer at high temperature, and has a higher free hole concentration, further improves the radiation recombination efficiency of electrons and holes, thereby enhancing the luminous efficiency, and more importantly, inserting an unintentionally doped GaN layer between the P-type AlGaN electron blocking layer and the high-temperature P-type GaN layer of the P-type GaN layer can cover the epitaxial defects extending from the bottom layer, and the unintentionally doped GaN layer can also serve as a buffer layer to reduce lattice mismatch and thermal mismatch, improve the overall crystal quality of the P-type GaN layer, and further enhance the antistatic ability of the semiconductor laser.

[0094] Through the description of the above implementation methods, those skilled in the art can clearly understand that the method for preparing a semiconductor laser can be implemented by means of software plus a necessary general hardware platform, and of course, can also be implemented by hardware. Based on this understanding, the above technical solution can essentially or in other words be embodied in the form of a software product that contributes to the prior art. The computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a magnetic disk, an optical disk, etc., and includes a number of instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A semiconductor laser, characterized in that: The semiconductor laser comprises a P-type GaN layer; the P-type GaN layer comprises a low-temperature P-type GaN layer, a P-type AIGaN electron blocking layer, an unintentionally doped GaN layer, a high-temperature P-type GaN layer and a P-type ohmic contact layer which are stacked in sequence from bottom to top; the P-type GaN layer is grown in a pure nitrogen atmosphere; The thickness of the unintentionally doped GaN layer is in a range of 50 nm to 100 nm.

2. A semiconductor laser according to claim 1, characterized in that: The thickness of the P-type AlGaN electron blocking layer is in a range of 50 nm to 150 nm.

3. A semiconductor laser according to claim 1 or 2, characterized in that: The semiconductor laser comprises a substrate, a buffer layer, an unintentionally doped layer, an N-type GaN layer, a shallow well layer, a light-emitting layer, the P-type GaN layer and an annealing layer which are stacked in sequence from bottom to top; Wherein, the shallow well layer includes a potential well layer and a potential barrier layer.

4. A semiconductor laser according to claim 3, characterized in that: The thickness of the P-type ohmic contact layer ranges from 3 nm to 150 nm.

5. A semiconductor laser according to claim 3, characterized in that: The thickness of the buffer layer is in a range of 2 nm to 8 nm.

6. A method for preparing a semiconductor laser according to any one of claims 1 to 5, characterized in that: The preparation method comprises: Select a substrate; growing an epitaxial layer on the substrate; In a pure nitrogen atmosphere, growing a P-type GaN layer on the epitaxial layer; The P-type GaN layer includes a low-temperature P-type GaN layer, a P-type AIGaN electron blocking layer, an unintentionally doped GaN layer, a high-temperature P-type GaN layer and a P-type ohmic contact layer grown sequentially from bottom to top; the thickness of the unintentionally doped GaN layer ranges from 50nm to 100nm.

7. The preparation method according to claim 6, characterized in that: The nitrogen flow rate range when growing the P-type AlGaN electron blocking layer is 100 sccm to 300 sccm; The nitrogen flow rate range when growing the unintentionally doped GaN layer is 150 sccm to 300 sccm; The nitrogen flow rate range when growing the high temperature P-type GaN layer is 150 sccm to 350 sccm.

8. The preparation method according to claim 6, characterized in that: The nitrogen flow rate range when growing the low-temperature P-type GaN layer is 100 sccm to 300 sccm; the nitrogen flow rate range when growing the P-type ohmic contact layer is 150 sccm to 300 sccm.

9. The preparation method according to any one of claims 6 to 8, characterized in that: The step of growing an epitaxial layer on the substrate comprises: growing a buffer layer having a thickness ranging from 2 nm to 8 nm on the substrate; growing an unintentionally doped layer having a thickness ranging from 1 μm to 2 μm on the buffer layer; An N-type GaN layer with a thickness ranging from 1.5 μm to 5.5 μm is grown on the unintentionally doped layer, wherein the N-type GaN layer is a highly Si-doped layer with a Si doping concentration ranging from 1×10 18 cm -3 Up to 10 19 cm -3 ; A shallow well layer is grown on the N-type GaN layer, wherein the shallow well layer includes a component of In X Ga 1-X N potential well layer and GaN barrier layer, where 0 <X<1; A light emitting layer is grown on the shallow well layer, wherein the light emitting layer comprises an InGaN well layer and a GaN barrier layer that are alternately stacked and grown, wherein the thickness of the InGaN well layer ranges from 2nm to 4nm, and the thickness of the GaN barrier layer ranges from 5nm to 10nm.

10. The preparation method according to claim 8, characterized in that: The method further comprises: In a pure nitrogen atmosphere, a semiconductor laser having a P-type GaN layer is annealed to form an annealed layer on the P-type ohmic contact layer; wherein the annealing temperature is between 500° C. and 750° C., and the nitrogen flow rate ranges from 250 sccm to 400 sccm.

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