Test method for judging laser characteristics of active layer of quantum well

Abstract

The embodiment of the invention provides a test method for judging the lasing characteristic of a quantum well active layer, and the method comprises the steps: selecting a substrate, sequentially growing a buffer layer and the quantum well active layer on the substrate, and obtaining an epitaxial wafer; performing a variable excitation power surface photoluminescence test on the epitaxial wafer, and collecting a luminescence spectrum; carrying out single-peak or multi-peak function fitting on each obtained luminescence spectrum to obtain the integral intensity and the line width of a narrow peak at the low-energy end of the quantum well; drawing a scatter diagram that the integral intensity of the narrow peak at the low-energy end of the quantum well changes along with the excitation power, and obtaining a starting point threshold value of the narrow peak through linear fitting; and comparing the starting point threshold values and the line widths of the narrow peaks of the plurality of epitaxial wafers, and predicting the lasing characteristic of the quantum well active layer based on a comparison result. According to the test method, the advantages and disadvantages of the quantum well active layer lasing characteristic can be rapidly judged, the test method is a nondestructive test, the operation process is simple, the stability of the test result is good, and the test time can be effectively saved.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor optoelectronic devices, and in particular to a testing method for judging the lasing characteristics of a quantum well active layer. Background Art

[0002] Ultraviolet light has a wide range of applications in disinfection, non-line-of-sight communications, phototherapy, material curing and other fields. Since the high-quality epitaxy of GaN thin films was achieved and GaN-based blue LEDs were subsequently prepared, wide-bandgap nitride semiconductor materials represented by AlN and GaN have received widespread attention. Compared with traditional ultraviolet light sources such as high-pressure mercury lamps and excimer lasers, AlGaN-based ultraviolet semiconductor lasers have outstanding advantages such as small size, easy integration, no pollution, long life, and fast response, and are expected to gradually replace traditional laser light sources in many fields.

[0003] AlGaN-based ultraviolet laser diodes, especially those in the UVC (200-280nm) and UVB (280-320nm) bands, have developed slowly. One of the key issues is that the crystal quality and interface flatness of the epitaxial layer are not ideal. Performing optically pumped edge emission tests on the grown multi-quantum well structure is an effective method to determine the lasing characteristics of the laser active region. However, the grown epitaxial wafers must first be cleaved and prepared into laser bars, and the lasing characteristics are easily affected by the effects of the cavity surface cleavage process and the configuration of the test system, resulting in a complex test process, long test time, and poor stability of the test results. Summary of the invention

[0004] In view of this, an embodiment of the present invention provides a test method for determining the lasing characteristics of a quantum well active layer, which is used to solve the problems of long test time and complicated test process in the existing test methods.

[0005] An embodiment of the present invention provides a test method for determining the lasing characteristics of a quantum well active layer, comprising:

[0006] Selecting a substrate, and sequentially growing a buffer layer and a quantum well active layer on the substrate to obtain an epitaxial wafer;

[0007] Performing a surface photoluminescence test on the epitaxial wafer with varying excitation power to collect a luminescence spectrum;

[0008] Performing single-peak or multi-peak function fitting on each acquired luminescence spectrum to obtain the integrated intensity and line width of the narrow peak at the low-energy end of the quantum well;

[0009] Draw a scatter plot of the integrated intensity of the narrow peak at the low energy end of the quantum well versus the excitation power, and obtain the starting threshold of the narrow peak by linear fitting;

[0010] The starting thresholds and line widths of the narrow peaks of the plurality of epitaxial wafers are compared, and based on the comparison results, the lasing characteristics of the quantum well active layer are predicted.

[0011] According to an embodiment of the present invention, the step of performing a surface photoluminescence test on the epitaxial wafer with varying excitation power and collecting a luminescence spectrum comprises:

[0012] The excitation light source emits a light beam to the epitaxial wafer, and the spectrometer collects the luminescence spectrum of the epitaxial wafer.

[0013] Wherein, the incident direction of the excitation light source and the collection direction of the luminescence spectrum are located on the same side of the epitaxial wafer; or

[0014] The incident direction of the excitation light source and the collection direction of the luminescence spectrum are located on two opposite sides of the epitaxial wafer.

[0015] According to an embodiment of the present invention, the collection direction of the luminescence spectrum is at a preset angle with the normal direction of the epitaxial wafer, and the preset angle ranges from 0 to 60 degrees.

[0016] According to an embodiment of the present invention, the step of obtaining the epitaxial wafer further includes:

[0017] The epitaxial wafer further includes an N-type confinement layer and an N-type waveguide layer, wherein the N-type confinement layer and the N-type waveguide layer are sequentially grown between the buffer layer and the quantum well active layer;

[0018] The epitaxial wafer further includes a P-type waveguide layer and a P-type confinement layer, and the P-type waveguide layer and the P-type confinement layer are sequentially grown on the quantum well active layer.

[0019] According to an embodiment of the present invention, the step of obtaining the epitaxial wafer further includes:

[0020] The epitaxial wafer further includes a P-type contact layer, wherein the P-type contact layer is grown on the P-type confinement layer; and / or

[0021] The epitaxial wafer further includes a transition layer, and the transition layer is grown between the buffer layer and the N-type confinement layer.

[0022] According to an embodiment of the present invention, the step of obtaining the epitaxial wafer further includes:

[0023] The epitaxial wafer further includes an N-type layer and a P-type layer, wherein the N-type layer is grown between the buffer layer and the quantum well active layer, and the P-type layer is grown on the quantum well active layer.

[0024] According to an embodiment of the present invention, the step of obtaining the epitaxial wafer further includes:

[0025] The epitaxial wafer further includes a P-type contact layer, wherein the P-type contact layer is grown on the P-type layer; and / or

[0026] The epitaxial wafer further includes a transition layer, and the transition layer is grown between the buffer layer and the N-type layer.

[0027] According to an embodiment of the present invention, the material of the substrate includes any one of sapphire, GaN, AlN, SiC and Si.

[0028] According to an embodiment of the present invention, the structure of the quantum well active layer includes any one of a double heterojunction structure, a single quantum well structure and a multiple quantum well structure.

[0029] According to an embodiment of the present invention, the process parameters for the epitaxial wafer growth include growth temperature, growth rate, pressure and a 5:3 ratio.

[0030] The test method for determining the lasing characteristics of the quantum well active layer provided by the embodiment of the present invention can at least achieve the following technical effects: by testing the starting threshold and line width of photoinduced stimulated emission on the surface of the epitaxial wafer, the quality of the lasing characteristics of the quantum well active layer of the ultraviolet laser can be quickly determined. The test method is a non-destructive test and does not involve bar processing and chip preparation. The operation process is simple and convenient, and the test results are stable. It can effectively save test time and is conducive to shortening the product development cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0032] Figure 1 A flow chart schematically shows a test method for determining the lasing characteristics of a quantum well active layer according to an embodiment of the present invention;

[0033] Figure 2 The schematic diagram of the structure of the epitaxial wafer of the ultraviolet laser according to the embodiment of the present invention is shown;

[0034] Figure 3 A schematic diagram schematically shows that the incident direction of the excitation light source and the collection direction of the luminescence spectrum according to an embodiment of the present invention are located on the same side of the epitaxial wafer;

[0035] Figure 4 Schematically shows one of the luminescence spectrum graphs collected by the testing method according to an embodiment of the present invention;

[0036] Figure 5 The second luminescence spectrum diagram collected by the testing method according to the embodiment of the present invention is schematically shown;

[0037] Figure 6A scatter plot showing the integrated intensity of the narrow peak at the low energy end of a quantum well as a function of the excitation power drawn according to the test method of an embodiment of the present invention is schematically shown;

[0038] Figure 7 A schematic diagram schematically shows that the incident direction of the excitation light source and the collection direction of the luminescence spectrum according to an embodiment of the present invention are located on opposite sides of the epitaxial wafer;

[0039] Figure 8 The schematic diagram of the structure of the epitaxial wafer of the ultraviolet light emitting diode according to the embodiment of the present invention is shown schematically.

[0040] Reference numerals:

[0041] 10: substrate; 20: buffer layer; 30: quantum well active layer; 40: N-type confinement layer; 50: N-type waveguide layer; 60: P-type waveguide layer; 70: P-type confinement layer; 80: N-type layer; 90: P-type layer; 100: epitaxial wafer; 200: pump laser; 300: spectrometer; 310: optical fiber. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings. 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.

[0043] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0044] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0045] Ultraviolet lasers have a wide range of applications in many fields. The crystal quality and interface flatness of the epitaxial layer are important factors affecting the performance of semiconductor optoelectronic devices. Pump edge emission testing of the grown multi-quantum well structure is an effective method to determine the lasing characteristics of the active layer. The testing method in the prior art requires that the grown epitaxial wafer be cleaved and prepared into laser bars first, and the lasing characteristics are easily affected by the cavity surface cleavage process effect and the test system configuration, resulting in poor stability of the test results, complex test process, and long test time, which leads to a long device development cycle.

[0046] Combine the following Figures 1 to 8 A test method for determining the lasing characteristics of a quantum well active layer according to an embodiment of the present invention is described.

[0047] like Figure 1 As shown, the test method for determining the lasing characteristics of the quantum well active layer provided by the embodiment of the present invention includes:

[0048] Step 110: selecting a substrate 10, and sequentially growing a buffer layer 20 and a quantum well active layer 30 on the substrate 10 to obtain an epitaxial wafer 100;

[0049] Step 120: performing a surface photoluminescence test on the epitaxial wafer 100 with varying excitation power, and collecting a luminescence spectrum;

[0050] Step 130: Performing single-peak or multi-peak function fitting on each acquired luminescence spectrum to obtain the integrated intensity and line width of the narrow peak at the low-energy end of the quantum well;

[0051] Step 140: draw a scatter plot of the integral intensity of the narrow peak at the low energy end of the quantum well versus the excitation power, and obtain the starting point threshold of the narrow peak by linear fitting;

[0052] Step 150: Compare the starting thresholds and line widths of the narrow peaks of the plurality of epitaxial wafers 100 , and predict the lasing characteristics of the quantum well active layer 30 based on the comparison results.

[0053] The testing method of the present invention can be used to test the lasing characteristics of the quantum well active layer 30 of the ultraviolet laser, and can also be used to test the luminescence characteristics of the quantum well active layer 30 of the ultraviolet light emitting diode. The testing method is described in detail in the following three embodiments, namely, Embodiment 1, Embodiment 2 and Embodiment 3.

[0054] Embodiments 1 and 2 test the lasing characteristics of the quantum well active layer 30 of the ultraviolet laser, and the difference between Embodiments 1 and 2 is that the positions of the pump laser 200 and the spectrometer 300 are different. Embodiment 3 tests the luminescence characteristics of the quantum well active layer 30 of the ultraviolet light emitting diode.

[0055] Embodiment 1

[0056] Step 110

[0057] like Figure 2 As shown, a substrate 10 is selected, and a buffer layer 20 and a quantum well active layer 30 of an ultraviolet laser are grown from bottom to top on the substrate 10 to obtain a complete epitaxial wafer 100 of an ultraviolet laser.

[0058] The substrate 10 may be any one of sapphire, GaN, AlN, SiC and Si, and may be any substrate that can grow nitride.

[0059] Preferably, the refractive index of the substrate 10 is smaller than that of the epitaxial layer, so that the light confinement factor of the quantum well active layer 30 is higher, the leakage mode problem of the substrate 10 is weaker, and it is more conducive to realizing low-threshold stimulated emission of the laser.

[0060] Buffer layer 20, the material of buffer layer 20 can be a single-layer single-component III-group nitride material, such as AlN, GaN, AlGaN. The material of buffer layer 20 can also be a multi-layer composite structure, including a sputtered seed layer, a low-temperature nucleation layer, a two-dimensional material insertion layer (such as graphene, hexagonal boron nitride and other two-dimensional insertion layers), a superlattice transition layer, a high-temperature annealing layer, a homoepitaxial layer and a high-temperature template layer, so as to improve the quality of the epitaxial layer and enhance the light confinement capability.

[0061] Optionally, the epitaxial wafer 100 further includes an N-type limiting layer 40, which may be omitted or grown on the buffer layer 20. a In b Ga 1-a-b N, 0<a<1, 0<b<1, can be a single-component III-group nitride; polarization doping can be used to induce a certain concentration of electrons by gradual component change, that is, at least one of a gradually increases and b gradually decreases along the metal polarity direction. Si can also be doped during the growth process to generate conductive electrons, and there is no fixed requirement for their distribution form in the N-type confinement layer 40. Si can also be left undoped, because there is a certain background electron concentration without intentional doping.

[0062] Optionally, the epitaxial wafer 100 further includes an N-type waveguide layer 50, which can be eliminated or grown on the N-type confinement layer 40. The N-type waveguide layer 50 is located between the N-type confinement layer 40 and the quantum well active layer 30. c In d Ga 1-c-dN, 0<c<1, 0<d<1, and its bandgap width is smaller than the bandgap width of the N-type confinement layer 40. The layer can be doped with Si to suppress point defects, or it can be undoped with Si to reduce the optical loss in the layer. The N-type waveguide layer 50 can be a single-component III-nitride thin film material, or a component gradient with a gradually increasing or decreasing bandgap width to induce free conductive electrons or further improve the optical confinement capability.

[0063] The quantum well active layer 30 may be a group III nitride double heterojunction structure: for example, a thick Al x In y Ga 1-x-y N / A x In y Ga 1-x-y N structure; it can also be a single quantum well structure: such as a thin single layer Al x In y Ga 1-x-y N structure; it can also be a multi-quantum well structure: such as a thin multi-period Al x In y Ga 1-x-y N / A x In y Ga 1-x-y N structure, wherein 0<x<1, 0<y<1.

[0064] Optionally, the epitaxial wafer 100 further includes a P-type waveguide layer 60, which can be eliminated or grown on the quantum well active layer 30. e In f Ga 1-e-f N, 0<e<1, 0<f<1, and its bandgap is preferably the same as the bandgap of the N-type confinement layer 40. The layer can be doped with Si to suppress point defects, or it can be undoped with Si to reduce the light loss in the layer. The P-type waveguide layer 60 can be a single-component III-nitride thin film material, or a component gradient with a gradually increasing or decreasing bandgap to induce free conductive holes or further improve the light confinement capability. The components of the P-type waveguide layer 60 are preferably the same as those of the N-type waveguide layer 50.

[0065] Optionally, the epitaxial wafer 100 further includes a P-type confinement layer 70. The P-type confinement layer 70 may be further grown on the P-type waveguide layer 60. The P-type confinement layer 70 is made of a III-group nitride material Al g In h Ga 1-g-hN, 0<g<1, 0<h<1, can be a single-component III-group nitride film; polarization doping can be used to induce a certain concentration of holes by gradual component change, that is, at least one of g gradually decreases and h gradually increases along the metal polarity direction. Mg can also be doped during the growth process to generate conductive holes, and there is no fixed requirement for their distribution form in the P-type confinement layer 70.

[0066] Optionally, the epitaxial wafer 100 further includes a P-type contact layer, which can continue to grow on the P-type confinement layer 70 . The P-type contact layer is usually a heavily doped P-type III-nitride thin layer to form a good metal / P-type semiconductor ohmic contact.

[0067] Optionally, a group III nitride film with a higher Al content may be grown between the quantum well active layer 30 and the N-type waveguide layer 50 and between the quantum well active layer 30 and the P-type waveguide layer 60 to achieve carrier blocking effect.

[0068] Optionally, a transition layer, such as a superlattice, a medium temperature layer, etc., made of a III-nitride material, may be inserted between the buffer layer 20 and the N-type confinement layer 40 to further filter material dislocations, release epitaxial stress, improve epitaxial morphology, and enhance the crystal quality of the N-type confinement layer 40 .

[0069] Step 120

[0070] After the complete ultraviolet laser epitaxial wafer 100 is obtained through epitaxial growth, a surface photoluminescence test with variable power can be directly performed without any processing.

[0071] The excitation light source emits a light beam to the surface of the epitaxial wafer 100, and the optical fiber 310 of the spectrometer 300 collects the luminescence spectrum on one side of the epitaxial wafer 100. The excitation light source includes a pump laser 200. In this embodiment, the pump laser 200 and the spectrometer 300 are located on the same side of the epitaxial wafer 100.

[0072] The incident direction of the excitation light source and the collection direction of the luminescence spectrum are on the same side of the epitaxial wafer 100, that is, the surface of the epitaxial wafer 100 is excited, and the optical fiber 310 collects the luminescence spectrum from the front of the epitaxial wafer 100. The incident direction of the excitation light source can maintain a certain angle with the epitaxial wafer 100, and the angle range is not limited. Figure 3 As shown in , the optical fiber 310 is located in the normal direction of the epitaxial wafer 100, and can also be on the left or right side of the normal direction. The collection direction of the luminescence spectrum is at a preset angle with the normal direction of the epitaxial wafer 100, that is, the collection direction maintains a certain angle with the normal direction, as shown by the angle θ, based on the ability to detect low energy peaks, and the range of the preset angle is preferably 0 to 60 degrees.

[0073] Variable excitation power can directly adjust the output energy or voltage of the laser to achieve variable power excitation; continuous or fixed attenuation plates can also be used to achieve variable power excitation by adding or removing attenuation plates at higher output energy.

[0074] Step 130

[0075] The luminescence spectrum of the epitaxial wafer 100 in which the buffer layer 20 is first grown on the substrate 10 and then the quantum well active layer 30 is directly grown is as follows: Figure 4 As shown, peak 1 corresponds to the luminescence peak of the quantum well active layer 30, and peak 2 is a narrow peak at the low energy end generated under a higher excitation power, and its integrated intensity and half-height width need to be fitted.

[0076] On the substrate 10, the buffer layer 20 is first grown, followed by the N-type confinement layer 40 and the N-type waveguide layer 50, then the quantum well active layer 30, and finally the P-type waveguide layer 60. The luminescence spectrum of the epitaxial wafer 100 is as follows: Figure 5 Peak 1 corresponds to the luminescence peak of the P-type waveguide layer 60, peak 2 corresponds to the luminescence peak of the quantum well active layer 30, and peak 3 is a narrow peak at the low energy end generated under a higher excitation power, and its integrated intensity and half-height width need to be fitted.

[0077] The fitting function mainly adopts peak type function, the common ones are: Gauss, Gaussian, Lorentz, Laplace, Person Ⅶ, Person Ⅳ, etc., for single peak or multi-peak fitting, and can fit and calculate the area and half-height width of narrow peaks.

[0078] Step 140

[0079] A scatter plot of the integrated intensity of the narrow peak at the low energy end of the quantum well versus the excitation power is drawn, and a linear fit is performed to obtain the starting threshold of the narrow peak.

[0080] Step 150

[0081] The starting thresholds and line widths of the narrow peaks of the plurality of epitaxial wafers 100 are compared, and based on the comparison results, the quality of the lasing characteristics of the quantum well active layer 30 is predicted.

[0082] Multiple epitaxial wafers 100 are formed under different growth processes, and the components and thicknesses of each layer of each epitaxial wafer 100 are the same. The growth process includes growth temperature, growth rate, pressure and 5:3 ratio, which indicates the ratio of group V source to group III source. The growth process has an important influence on the quality of the lasing characteristics of the quantum well active layer 30 of the epitaxial wafer 100.

[0083] The epitaxial wafer 100 with a smaller starting threshold and line width obtained by fitting calculation has better lasing characteristics of the quantum well active layer 30. Under similar structures, the optical confinement ability is the same, and the smaller the starting threshold and line width of surface stimulated emission, the smaller the internal loss. Under the condition of the same edge emission cavity surface loss, the epitaxial wafer 100 with smaller internal loss has better lasing characteristics. Therefore, by comparing the starting threshold and line width of the narrow peaks of multiple epitaxial wafers 100, the epitaxial wafer 100 with the best lasing characteristics of the quantum well active layer 30 can be obtained.

[0084] Figure 6 The narrow peak integrated intensity fitting scatter plot of the epitaxial wafer 100 with the same epitaxial structure grown using templates with different dislocation densities is shown. The line widths of the epitaxial wafer 100 on the low dislocation density and high dislocation density templates are 1.22 nanometers and 1.68 nanometers, respectively. It can be seen that the epitaxial wafer 100 on the low dislocation density template has a smaller starting threshold and line width.

[0085] In this embodiment, by testing the starting threshold and line width of photoinduced stimulated emission on the surface of the epitaxial wafer 100, the quality of the lasing characteristics of the quantum well active layer 30 of the ultraviolet laser can be quickly judged. The testing method is a non-destructive test and does not involve bar processing and chip preparation. The operation process is simple and convenient, and the test results are stable. It can effectively save testing time and is conducive to shortening the product development cycle.

[0086] Embodiment 2

[0087] Step 110

[0088] like Figure 2 As shown, a substrate 10 is selected, and a buffer layer 20 and a quantum well active layer 30 of an ultraviolet laser are grown from bottom to top on the substrate 10 to obtain a complete epitaxial wafer 100 of an ultraviolet laser.

[0089] The substrate 10 may be any one of sapphire, GaN, AlN, SiC and Si, and may be any substrate capable of growing nitrides. The substrate 10 having a light-transmitting back surface is preferred.

[0090] Preferably, the refractive index of the substrate 10 is smaller than that of the epitaxial layer, so that the light confinement factor of the quantum well active layer 30 is higher, the leakage mode problem of the substrate 10 is weaker, and it is more conducive to realizing low-threshold stimulated emission of the laser.

[0091] Buffer layer 20, the material of buffer layer 20 can be a single-layer single-component III-group nitride material, such as AlN, GaN, AlGaN. The material of buffer layer 20 can also be a multi-layer composite structure, including a sputtered seed layer, a low-temperature nucleation layer, a two-dimensional material insertion layer (such as graphene, hexagonal boron nitride and other two-dimensional insertion layers), a superlattice transition layer, a high-temperature annealing layer, a homoepitaxial layer and a high-temperature template layer, so as to improve the quality of the epitaxial layer and enhance the light confinement capability.

[0092] Optionally, the epitaxial wafer 100 further includes an N-type limiting layer 40, which may be omitted or grown on the buffer layer 20. a In b Ga 1-a-b N, 0<a<1, 0<b<1, can be a single-component III-group nitride; polarization doping can be used to induce a certain concentration of electrons by gradual component change, that is, at least one of a gradually increases and b gradually decreases along the metal polarity direction. Si can also be doped during the growth process to generate conductive electrons, and there is no fixed requirement for their distribution form in the N-type confinement layer 40. Si can also be left undoped, because there is a certain background electron concentration without intentional doping.

[0093] Optionally, the epitaxial wafer 100 further includes an N-type waveguide layer 50, which can be eliminated or grown on the N-type confinement layer 40. The N-type waveguide layer 50 is located between the N-type confinement layer 40 and the quantum well active layer 30. c In d Ga 1-c-d N, 0<c<1, 0<d<1, and its bandgap width is smaller than the bandgap width of the N-type confinement layer 40. The layer can be doped with Si to suppress point defects, or it can be undoped with Si to reduce the optical loss in the layer. The N-type waveguide layer 50 can be a single-component III-nitride thin film material, or a component gradient with a gradually increasing or decreasing bandgap width to induce free conductive electrons or further improve the optical confinement capability.

[0094] The quantum well active layer 30 may be a group III nitride double heterojunction structure: for example, a thick Al x In y Ga 1-x-y N / A x In y Ga 1-x-y N structure; it can also be a single quantum well structure: such as a thin single layer Al x In y Ga 1-x-y N structure; it can also be a multi-quantum well structure: such as a thin multi-period Al x In y Ga1-x-y N / A x In y Ga 1-x-y N structure, wherein 0<x<1, 0<y<1.

[0095] Optionally, the epitaxial wafer 100 further includes a P-type waveguide layer 60, which can be eliminated or grown on the quantum well active layer 30. e In f Ga 1-e-f N, 0<e<1, 0<f<1, and its bandgap is preferably the same as the bandgap of the N-type confinement layer 40. The layer can be doped with Si to suppress point defects, or it can be undoped with Si to reduce the light loss in the layer. The P-type waveguide layer 60 can be a single-component III-nitride thin film material, or a component gradient with a gradually increasing or decreasing bandgap to induce free conductive holes or further improve the light confinement capability. The components of the P-type waveguide layer 60 are preferably the same as those of the N-type waveguide layer 50.

[0096] Optionally, the epitaxial wafer 100 further includes a P-type confinement layer 70. The P-type confinement layer 70 may be further grown on the P-type waveguide layer 60. The P-type confinement layer 70 is made of a III-group nitride material Al g In h Ga 1-g-h N, 0<g<1, 0<h<1, can be a single-component III-group nitride film; polarization doping can be used to induce a certain concentration of holes by gradual component change, that is, at least one of g gradually decreases and h gradually increases along the metal polarity direction. Mg can also be doped during the growth process to generate conductive holes, and there is no fixed requirement for their distribution form in the P-type confinement layer 70.

[0097] Optionally, the epitaxial wafer 100 further includes a P-type contact layer, which can continue to grow on the P-type confinement layer 70 . The P-type contact layer is usually a heavily doped P-type III-nitride thin layer to form a good metal / P-type semiconductor ohmic contact.

[0098] Optionally, a group III nitride film with a higher Al content may be grown between the quantum well active layer 30 and the N-type waveguide layer 50 and between the quantum well active layer 30 and the P-type waveguide layer 60 to achieve carrier blocking effect.

[0099] Optionally, a transition layer, such as a superlattice, a medium temperature layer, etc., made of a III-nitride material, may be inserted between the buffer layer 20 and the N-type confinement layer 40 to further filter material dislocations, release epitaxial stress, improve epitaxial morphology, and enhance the crystal quality of the N-type confinement layer 40 .

[0100] Step 120

[0101] After the complete epitaxial wafer 100 of the ultraviolet laser is obtained by epitaxial growth, a surface photoluminescence test with variable power can be performed without any processing. In this embodiment, the pump laser 200 and the spectrometer 300 are located on opposite sides of the epitaxial wafer 100 .

[0102] The incident direction of the excitation light source and the collection direction of the luminescence spectrum are on opposite sides of the epitaxial wafer 100, that is, the surface of the epitaxial wafer 100 is excited, and the optical fiber 310 collects the luminescence spectrum from the back of the epitaxial wafer 100. The incident direction of the excitation light source can maintain a certain angle with the epitaxial wafer 100, and the angle range is not limited. Figure 7 As shown in , the optical fiber 310 is located in the normal direction of the epitaxial wafer 100, and can also be on the left or right side of the normal direction. The collection direction of the luminescence spectrum is at a preset angle with the normal direction of the epitaxial wafer 100, that is, the collection direction maintains a certain angle with the normal direction, as shown by the angle θ, based on the ability to detect low energy peaks, and the range of the preset angle is preferably 0 to 60 degrees.

[0103] Variable excitation power can directly adjust the output energy or voltage of the laser to achieve variable power excitation; continuous or fixed attenuation plates can also be used to achieve variable power excitation by adding or removing attenuation plates at higher output energy.

[0104] Step 130

[0105] The luminescence spectrum of the epitaxial wafer 100 in which the buffer layer 20 is first grown on the substrate 10 and then the quantum well active layer 30 is directly grown is as follows: Figure 4 As shown, peak 1 corresponds to the luminescence peak of the quantum well active layer 30, and peak 2 is a narrow peak at the low energy end generated under a higher excitation power, and its integrated intensity and half-height width need to be fitted.

[0106] On the substrate 10, the buffer layer 20 is first grown, followed by the N-type confinement layer 40 and the N-type waveguide layer 50, then the quantum well active layer 30, and finally the P-type waveguide layer 60. The luminescence spectrum of the epitaxial wafer 100 is as follows: Figure 5 Peak 1 corresponds to the luminescence peak of the P-type waveguide layer 60, peak 2 corresponds to the luminescence peak of the quantum well active layer 30, and peak 3 is a narrow peak at the low energy end generated under a higher excitation power, and its integrated intensity and half-height width need to be fitted.

[0107] The fitting function mainly adopts peak type function, the common ones are: Gauss, Gaussian, Lorentz, Laplace, Person Ⅶ, Person Ⅳ, etc., for single peak or multi-peak fitting, and can fit and calculate the area and half-height width of narrow peaks.

[0108] Step 140

[0109] A scatter plot of the integrated intensity of the narrow peak at the low energy end of the quantum well versus the excitation power is drawn, and a linear fit is performed to obtain the starting threshold of the narrow peak.

[0110] Step 150

[0111] The starting thresholds and line widths of the narrow peaks of the plurality of epitaxial wafers 100 are compared, and based on the comparison results, the quality of the lasing characteristics of the quantum well active layer 30 is predicted. The plurality of epitaxial wafers 100 are formed under different growth processes, and the components and thicknesses of the layers of each epitaxial wafer 100 are the same.

[0112] The epitaxial wafer 100 with a smaller starting threshold and line width obtained by fitting calculation has better lasing characteristics of the quantum well active layer 30. Under similar structures, the optical confinement ability is the same, and the smaller the starting threshold and line width of surface stimulated emission, the smaller the internal loss. Under the condition of the same edge emission cavity surface loss, the epitaxial wafer 100 with smaller internal loss has better lasing characteristics. Therefore, by comparing the starting threshold and line width of the narrow peaks of multiple epitaxial wafers 100, the epitaxial wafer 100 with the best lasing characteristics of the quantum well active layer 30 can be obtained.

[0113] Figure 6 The narrow peak integrated intensity fitting scatter plot of the epitaxial wafer 100 with the same epitaxial structure grown using templates with different dislocation densities is shown. The line widths of the epitaxial wafer 100 on the low dislocation density and high dislocation density templates are 1.22 nanometers and 1.68 nanometers, respectively. It can be seen that the epitaxial wafer 100 on the low dislocation density template has a smaller starting threshold and line width.

[0114] Embodiment 3

[0115] Step 110

[0116] like Figure 8 As shown, a substrate 10 is selected, and a buffer layer 20 and a quantum well active layer 30 of an ultraviolet light emitting diode are grown from bottom to top on the substrate 10 to obtain a complete epitaxial wafer 100 of an ultraviolet light emitting diode.

[0117] The substrate 10 may be any one of sapphire, GaN, AlN, SiC and Si, and may be any substrate 10 that can grow nitride. A substrate 10 with a light-transmitting back surface is preferred.

[0118] Buffer layer 20, the material of buffer layer 20 can be a single-layer single-component III-group nitride material, such as AlN, GaN, AlGaN. The material of buffer layer 20 can also be a multi-layer composite structure, including a sputtered seed layer, a low-temperature nucleation layer, a two-dimensional material insertion layer (such as graphene, hexagonal boron nitride and other two-dimensional insertion layers), a superlattice transition layer, a high-temperature annealing layer, a homoepitaxial layer and a high-temperature template layer, so as to improve the quality of the epitaxial layer and enhance the light confinement capability.

[0119] Optionally, the epitaxial wafer 100 further includes an N-type layer 80, which is grown on the buffer layer 20 and located between the buffer layer 20 and the quantum well active layer 30. The N-type layer 80 is made of a III-group nitride material Al j In k Ga 1-j-k N, 0<j<1, 0<k<1, can be a single-component III-group nitride film; polarization doping can be used to induce a certain concentration of electrons by gradual component change, that is, at least one of j gradually increases and k gradually decreases along the metal polarity direction. Si can also be doped during the growth process to generate conductive electrons, and there is no fixed requirement for their distribution form in the N-type confinement layer 40. Si can also be left undoped, because there is a certain background electron concentration without intentional doping.

[0120] The quantum well active layer 30 may be a group III nitride double heterojunction structure: for example, a thick Al m In n Ga 1-m-n N / A m In n Ga 1-m-n N structure; it can also be a single quantum well structure: such as a thin single layer Al m In n Ga 1-m-n N structure; it can also be a multi-quantum well structure: such as a thin multi-period Al m In n Ga 1-m-n N / A m In n Ga 1-m-n N structure, wherein 0<m<1, 0<n<1.

[0121] Optionally, the epitaxial wafer 100 further includes a P-type layer 90, which is grown on the quantum well active layer 30. The P-type layer 90 is made of a III-group nitride material Al p In q Ga 1-p-q N, 0<p<1, 0<q<1, can be a single-component III-group nitride film; polarization doping can be used to induce a certain concentration of holes by gradual component change, that is, at least one of p gradually decreases and q gradually increases along the metal polarity direction. Mg can also be doped during the growth process to generate conductive holes, and there is no fixed requirement for their distribution form in the P-type confinement layer 70.

[0122] Optionally, the epitaxial wafer 100 further includes a P-type contact layer, which can continue to be grown on the P-type layer 90 . The P-type contact layer is usually a heavily doped P-type III-nitride thin layer to form a good metal / P-type semiconductor ohmic contact.

[0123] Optionally, a group III nitride film with a higher Al content may be grown between the quantum well active layer 30 and the N-type layer 80 and between the quantum well active layer 30 and the P-type layer 90 to achieve a carrier blocking effect.

[0124] Optionally, a transition layer, such as a superlattice, a medium temperature layer, etc., made of a III-nitride material, may be inserted between the buffer layer 20 and the N-type layer 80 to further filter material dislocations, release epitaxial stress, improve epitaxial morphology, and enhance the crystal quality of the N-type layer 80 .

[0125] Furthermore, after the entire epitaxial wafer 100 structure is grown, the quantum well active layer structure can be peeled off and a thin film structure with a lower refractive index can be plated on both sides thereof. It is only necessary to ensure that a thin film structure with a lower refractive index exists on the upper and lower sides of the quantum well active layer 30 .

[0126] Step 120

[0127] After the complete ultraviolet light emitting diode epitaxial wafer 100 is obtained through epitaxial growth, a surface photoluminescence test with variable power can be performed without any processing.

[0128] Furthermore, as described in step 110 , the quantum well active layer structure can be obtained by electrochemical etching, two-dimensional material stripping and other methods, and it is only necessary to ensure that thin film materials with lower refractive index exist on the upper and lower sides of the quantum well active layer 30 .

[0129] Optionally, the incident direction of the excitation light source and the collection direction of the luminescence spectrum are on opposite sides of the epitaxial wafer 100, that is, the surface of the epitaxial wafer 100 is excited, and the optical fiber 310 collects the luminescence spectrum from the back of the epitaxial wafer 100. The incident direction of the excitation light source can maintain a certain angle with the epitaxial wafer 100, and the angle range is not limited. Figure 7 As shown in , the optical fiber 310 is located in the normal direction of the epitaxial wafer 100, or on the left or right side of the normal direction. The collection direction of the luminous spectrum is at a preset angle to the normal direction of the epitaxial wafer 100, and the preset angle range is preferably 0-60 degrees.

[0130] Optionally, the incident direction of the excitation light source and the collection direction of the luminescence spectrum are on the same side of the epitaxial wafer 100, that is, the surface of the epitaxial wafer 100 is excited, and the optical fiber 310 collects the luminescence spectrum from the front of the epitaxial wafer 100. The incident direction of the excitation light source can maintain a certain angle with the epitaxial wafer 100, and the angle range is not limited. Figure 3As shown in , the optical fiber 310 is located in the normal direction of the epitaxial wafer 100, or on the left or right side of the normal direction. The collection direction of the luminous spectrum is at a preset angle to the normal direction of the epitaxial wafer 100, and the preset angle range is preferably 0-60 degrees.

[0131] Variable excitation power can directly adjust the output energy or voltage of the laser to achieve variable power excitation; continuous or fixed attenuation plates can also be used to achieve variable power excitation by adding or removing attenuation plates at higher output energy.

[0132] Step 130

[0133] Single-peak or multi-peak function fitting is performed on each luminescence spectrum obtained to obtain the integrated intensity and line width of the narrow peak at the low-energy end of the quantum well.

[0134] The fitting function mainly adopts peak type function, the common ones are: Gauss, Gaussian, Lorentz, Laplace, Person Ⅶ, Person Ⅳ, etc., for single peak or multi-peak fitting, and can fit and calculate the area and half-height width of narrow peaks.

[0135] Step 140

[0136] A scatter plot of the integrated intensity of the narrow peak at the low energy end of the quantum well versus the excitation power is drawn, and a linear fit is performed to obtain the starting threshold of the narrow peak.

[0137] Step 150

[0138] The starting thresholds and line widths of the narrow peaks of the plurality of epitaxial wafers 100 are compared, and based on the comparison results, the quality of the light emitting characteristics of the quantum well active layer 30 is predicted.

[0139] Multiple epitaxial wafers 100 are formed under different growth processes, and the components and thicknesses of each layer of each epitaxial wafer 100 are the same. The growth process includes growth temperature, growth rate, pressure, and 5:3 ratio, etc. The growth process has an important influence on the quality of the light-emitting characteristics of the quantum well active layer 30 of the epitaxial wafer 100.

[0140] The epitaxial wafer 100 with a smaller starting threshold and line width obtained by fitting calculation has better luminescence characteristics of the quantum well active layer 30. Under similar structures, the smaller the starting threshold and line width of surface stimulated emission, the smaller the internal loss, and the better the luminescence characteristics of the quantum well active layer 30.

[0141] Figure 6The narrow peak integrated intensity fitting scatter plot of the epitaxial wafer 100 with the same epitaxial structure grown using templates with different dislocation densities is shown. The line widths of the epitaxial wafer 100 on the low dislocation density and high dislocation density templates are 1.22 nanometers and 1.68 nanometers, respectively. It can be seen that the epitaxial wafer 100 on the low dislocation density template has a smaller starting threshold and line width.

[0142] In this embodiment, by testing the starting threshold and line width of photoinduced stimulated emission on the surface of the epitaxial wafer 100, the quality of the luminescence characteristics of the quantum well active layer 30 of the ultraviolet light-emitting diode can be quickly judged. The testing method is a non-destructive test, which does not involve bar processing and chip preparation process. The operation process is simple and the test results are stable, which can effectively save testing time and help shorten the product development cycle.

[0143] The above is only a specific embodiment of the present invention, but the protection scope of this application is not limited thereto. Any changes or substitutions made within the spirit and principle of the present invention should be included in the protection scope of this application. Therefore, the protection scope of this application should be based on the protection scope of the claims.

Claims

1. A test method for determining the lasing characteristics of a quantum well active layer, characterized in that: include: Selecting a substrate, and sequentially growing a buffer layer and a quantum well active layer on the substrate to obtain an epitaxial wafer; Performing a surface photoluminescence test on the epitaxial wafer with varying excitation power to collect a luminescence spectrum; Performing single-peak or multi-peak function fitting on each acquired luminescence spectrum to obtain the integrated intensity and line width of the narrow peak at the low-energy end of the quantum well; Draw a scatter plot of the integrated intensity of the narrow peak at the low energy end of the quantum well versus the excitation power, and obtain the starting threshold of the narrow peak by linear fitting; The starting thresholds and line widths of the narrow peaks of the plurality of epitaxial wafers are compared, and based on the comparison results, the lasing characteristics of the quantum well active layer are predicted.

2. The testing method according to claim 1, characterized in that: The step of performing a surface photoluminescence test on the epitaxial wafer with varying excitation power and collecting a luminescence spectrum comprises: The excitation light source emits a light beam to the epitaxial wafer, and the spectrometer collects the luminescence spectrum of the epitaxial wafer. Wherein, the incident direction of the excitation light source and the collection direction of the luminescence spectrum are located on the same side of the epitaxial wafer; or The incident direction of the excitation light source and the collection direction of the luminescence spectrum are located on two opposite sides of the epitaxial wafer.

3. The testing method according to claim 2, characterized in that: The collection direction of the luminescence spectrum is at a preset angle to the normal direction of the epitaxial wafer, and the preset angle ranges from 0 to 60 degrees.

4. The testing method according to claim 1, characterized in that: The step of obtaining the epitaxial wafer also includes: The epitaxial wafer further includes an N-type confinement layer and an N-type waveguide layer, wherein the N-type confinement layer and the N-type waveguide layer are sequentially grown between the buffer layer and the quantum well active layer; The epitaxial wafer further includes a P-type waveguide layer and a P-type confinement layer, and the P-type waveguide layer and the P-type confinement layer are sequentially grown on the quantum well active layer.

5. The testing method according to claim 4, characterized in that: The step of obtaining the epitaxial wafer also includes: The epitaxial wafer further includes a P-type contact layer, wherein the P-type contact layer is grown on the P-type confinement layer; and / or The epitaxial wafer further includes a transition layer, and the transition layer is grown between the buffer layer and the N-type confinement layer.

6. The testing method according to claim 1, characterized in that: The step of obtaining the epitaxial wafer also includes: The epitaxial wafer further includes an N-type layer and a P-type layer, wherein the N-type layer is grown between the buffer layer and the quantum well active layer, and the P-type layer is grown on the quantum well active layer.

7. The testing method according to claim 6, characterized in that: The step of obtaining the epitaxial wafer also includes: The epitaxial wafer further includes a P-type contact layer, wherein the P-type contact layer is grown on the P-type layer; and / or The epitaxial wafer further includes a transition layer, and the transition layer is grown between the buffer layer and the N-type layer.

8. The testing method according to any one of claims 1 to 7, characterized in that: The material of the substrate includes any one of sapphire, GaN, AlN, SiC and Si.

9. The testing method according to any one of claims 1 to 7, characterized in that: The structure of the quantum well active layer includes any one of a double heterojunction structure, a single quantum well structure and a multi-quantum well structure.

10. The testing method according to any one of claims 1 to 7, characterized in that: The process parameters for the epitaxial wafer growth include growth temperature, growth rate, pressure and 5:3 ratio.

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