Method for judging quantum well active layer lasing characteristics

Abstract

Embodiments of the present application provide a test method for judging lasing characteristics of quantum well active layer, comprising: selecting a substrate, growing a buffer layer and a quantum well active layer on the substrate in sequence to obtain an epitaxial wafer; performing surface photoluminescence test on the epitaxial wafer under variable excitation power, and collecting luminescence spectra; performing single-peak or multi-peak function fitting on each of the obtained luminescence spectra to obtain integral intensity and line width of narrow peak at low-energy end of the quantum well; drawing a scatter plot of integral intensity of the narrow peak at the low-energy end of the quantum well varying with excitation power, and obtaining a starting threshold of the narrow peak by linear fitting; comparing the starting threshold and the line width of the narrow peak of a plurality of epitaxial wafers, and predicting lasing characteristics of the quantum well active layer based on the comparison result. The test method of the present application can quickly judge the advantages and disadvantages of lasing characteristics of the quantum well active layer, the test method is a non-destructive test, the operation process is simple, the test result has good stability, and the test time can be effectively saved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor optoelectronic devices, and in particular to a test method for judging lasing characteristics of a quantum well active layer. BACKGROUND

[0002] Ultraviolet light has wide applications in the fields of disinfection and sterilization, non-line-of-sight communication, phototherapy, material curing, etc. Since high-quality epitaxy of GaN thin film was achieved, and GaN-based blue LEDs were subsequently prepared, wide-bandgap nitride semiconductor materials represented by AlN and GaN have attracted 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 service life, and fast response, and are expected to gradually replace traditional laser light sources in many fields.

[0003] AlGaN-based ultraviolet laser diodes, especially in the UVC (200-280 nm) and UVB (280-320 nm) bands, have developed slowly, and one of the key problems is that the crystal quality and interface flatness of the epitaxial layer are not ideal. Performing optical pumping edge emission testing on the grown multi-quantum well structure is an effective method for judging the lasing characteristics of the active region of the laser. However, the epitaxial wafer after growth needs to be cleaved and prepared into a laser bar, and the lasing characteristics are easily affected by the cleaving process effect of the cavity surface and the configuration of the test system, resulting in a complex testing process, long testing time, and poor stability of the test results. SUMMARY

[0004] Therefore, embodiments of the present application provide a test method for judging lasing characteristics of a quantum well active layer, which solves the problems of long testing time and complex testing process of the existing test method.

[0005] Embodiments of the present application provide a test method for judging lasing characteristics of a quantum well active layer, comprising:

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

[0007] performing surface photoluminescence testing with variable excitation power on the epitaxial wafer to collect luminescence spectra;

[0008] performing single-peak or multi-peak function fitting on each of the obtained luminescence spectra to obtain integral intensity and line width of a narrow peak at a low-energy end of the quantum well;

[0009] plotting a scatter plot of the integral intensity of the narrow peak at the low-energy end of the quantum well varying with the excitation power, and obtaining a threshold value of the appearance of the narrow peak through linear fitting;

[0010] The threshold of the start point of the narrow peak and the line width of the plurality of epitaxial wafers are compared, and based on the comparison result, the lasing characteristics of the quantum well active layer are predicted.

[0011] According to an embodiment of the present application, the surface photoluminescence test of the epitaxial wafer under the variable excitation power comprises the following steps:

[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] 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; or

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

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

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

[0017] The epitaxial wafer further comprises an N-type confinement layer and an N-type waveguide layer, and 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 comprises 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 application, the step of obtaining the epitaxial wafer further comprises:

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

[0021] The epitaxial wafer further comprises 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 application, the step of obtaining the epitaxial wafer further comprises:

[0023] The epitaxial wafer further comprises an N-type layer and a P-type layer, and 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 application, the step of obtaining the epitaxial wafer further comprises:

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

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

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

[0028] According to an embodiment of the present application, the structure of the quantum well active layer comprises any one of a double heterojunction structure, a single quantum well structure and a multi-quantum well structure.

[0029] According to an embodiment of the present application, the process parameters of the epitaxial wafer growth comprise a growth temperature, a growth speed, a pressure and a V / III ratio.

[0030] The test method for judging the lasing characteristics of the quantum well active layer provided by the embodiments of the present application can at least achieve the following technical effects: the advantages and disadvantages of the lasing characteristics of the quantum well active layer of the ultraviolet laser can be quickly judged by testing the starting threshold and the line width of the surface light-induced stimulated emission of the epitaxial wafer, the test method is a non-destructive test, does not involve the bar processing and chip preparation process, the operation process is simple, convenient and the test result has good stability, the test time can be effectively saved, and the product development cycle can be shortened. BRIEF DESCRIPTION OF DRAWINGS

[0031] The above and other objects, features and advantages of the present application will become more apparent from the following description of embodiments of the present application, taken in conjunction with the accompanying drawings, in which:

[0032] Figure 1 A flowchart of the test method for judging the lasing characteristics of the quantum well active layer according to an embodiment of the present application is schematically shown;

[0033] Figure 2 A structural schematic diagram of the epitaxial wafer of the ultraviolet laser according to an embodiment of the present application is schematically shown;

[0034] Figure 3 A schematic diagram in which 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 according to an embodiment of the present application is schematically shown;

[0035] Figure 4 One of the luminescence spectrum graphs collected by the test method according to an embodiment of the present application is schematically shown;

[0036] Figure 5 The second luminescence spectrum graph collected by the test method according to an embodiment of the present application is schematically shown;

[0037] Figure 6The scatter plot of the integral intensity of the quantum well low-energy end narrow peak plotted by the test method according to the embodiment of the present application is schematically shown as a function of the excitation power;

[0038] Figure 7 The schematic diagram of the incident direction of the excitation light source and the collection direction of the luminescence spectrum being located on the opposite sides of the epitaxial wafer is schematically shown according to the embodiment of the present application;

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

[0040] Reference signs:

[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] To make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0043] The terms used herein are only used to describe the specific embodiments, and are not intended to limit the present application. The terms "comprise", "contain", and the like used herein indicate the existence of the described 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 application, it should be noted that, unless otherwise explicitly specified and limited, the terms "mount", "connect", "connection" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0045] Ultraviolet laser has wide applications in many fields, and the crystal quality and interface flatness of the epitaxial layer are important factors affecting the performance of semiconductor optoelectronic devices. Pumping edge emission testing of the grown multi-quantum well structure is an effective method to judge the lasing characteristics of the active layer. The existing testing method needs to first cleave the grown epitaxial wafer and prepare a laser bar, and the lasing characteristics are easily affected by the cleaving process effect of the cavity surface and the configuration of the testing system, resulting in poor stability of the test results, complex testing process, and long testing time, which leads to a long development cycle of the device.

[0046] The embodiments of the present application are described below. Figures 1 to 8 The present application provides a test method for judging the lasing characteristics of a quantum well active layer.

[0047] As shown in Figure 1 The test method for judging the lasing characteristics of a quantum well active layer provided by the embodiments of the present application comprises:

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

[0049] Step 120: performing surface photoluminescence testing with variable excitation power on the epitaxial wafer 100, and collecting luminescence spectra;

[0050] Step 130: performing single-peak or multi-peak function fitting on each of the obtained luminescence spectra, and obtaining the integral intensity and line width of the narrow peak at the low-energy end of the quantum well;

[0051] Step 140: plotting 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 obtaining the starting threshold of the narrow peak by linear fitting;

[0052] Step 150: comparing the starting threshold and the line width of the narrow peak of a plurality of epitaxial wafers 100, and predicting the lasing characteristics of the quantum well active layer 30 based on the comparison result.

[0053] The test method of the present application can be used to test the lasing characteristics of the quantum well active layer 30 of an ultraviolet laser, and can also be used to test the luminescence characteristics of the quantum well active layer 30 of an ultraviolet light emitting diode. The test method is described in detail in three embodiments, namely embodiment one, embodiment two and embodiment three.

[0054] Embodiments one and two are used to test the lasing characteristics of the quantum well active layer 30 of an ultraviolet laser, and the difference between embodiments one and two is that the positions of the pumping laser 200 and the spectrometer 300 are different. Embodiment three is used to test the luminescence characteristics of the quantum well active layer 30 of an ultraviolet light emitting diode.

[0055] Embodiment one

[0056] Step 110

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

[0058] The substrate 10 can be selected from any one of sapphire, GaN, AlN, SiC and Si, and can also be extended to any substrate that can grow nitride.

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

[0060] The buffer layer 20 can be a single layer of a single component III-nitride material, such as AlN, GaN, AlGaN. The material of the 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 a two-dimensional insertion layer such as graphene, hexagonal boron nitride, etc.), a superlattice transition layer, a high-temperature annealing layer, a homoepitaxial layer and a high-temperature template layer, to improve the quality of the epitaxial layer and enhance the light confinement capability.

[0061] Optionally, the epitaxial wafer 100 further comprises an N-type confinement layer 40, which can be cancelled or grown on the buffer layer 20. It is made of III-nitride material Al a In b Ga 1-a-b N, 0 < a < 1, 0 < b < 1, which can be a single component III-nitride; polarization doping can be used to induce a certain concentration of electrons by gradually changing the composition, i.e. at least one of a gradually increasing and b gradually decreasing along the metal-polar direction. Si can also be doped during growth to produce conductive electrons, which have no fixed requirements for distribution in the N-type confinement layer 40. It can also not be doped with Si, as there is a certain background electron concentration under unintentional doping.

[0062] Optionally, the epitaxial wafer 100 further comprises an N-type waveguide layer 50, which can be cancelled or grown on the N-type confinement layer 40, and the N-type waveguide layer 50 is located between the N-type confinement layer 40 and the quantum well active layer 30. It is made of III-nitride material Al c In d Ga 1-c-dN, 0 < c < 1, 0 < d < 1, and the band gap is smaller than that of the N-type confinement layer 40. The layer can be doped with Si to suppress point defects, or undoped to reduce optical loss in the layer. The N-type waveguide layer 50 can be a single composition III-nitride thin film material, or a compositionally graded layer with gradually increasing or decreasing band gap to induce free conducting electrons or to further enhance optical confinement.

[0063] The quantum well active layer 30 can be a double heterostructure III-nitride structure, such as a thick Al x In y Ga 1-x-y N / Al x In y Ga 1-x-y N structure; or a single quantum well structure, such as a thin single layer Al x In y Ga 1-x-y N structure; or a multiple quantum well structure, such as a thin multiple period Al x In y Ga 1-x-y N / Al x In y Ga 1-x-y N structure, where 0 < x < 1, 0 < y < 1.

[0064] Optionally, the epitaxial wafer 100 further includes a P-type waveguide layer 60, which can be omitted or grown on top of the quantum well active layer 30. It is made of III-nitride material Al e In f Ga 1-e-f N, 0 < e < 1, 0 < f < 1, and the band gap is preferably the same as that of the N-type confinement layer 40. The layer can be doped with Si to suppress point defects, or undoped to reduce optical loss in the layer. The P-type waveguide layer 60 can be a single composition III-nitride thin film material, or a compositionally graded layer with gradually increasing or decreasing band gap to induce free conducting holes or to further enhance optical confinement. The composition of the P-type waveguide layer 60 is preferably the same as that of the N-type waveguide layer 50.

[0065] Optionally, the epitaxial wafer 100 further includes a P-type confinement layer 70, which can be grown on top of the P-type waveguide layer 60. It is made of III-nitride material Al g In h Ga 1-g-hN is made of a single component III-nitride film, 0 < g < 1, 0 < h < 1, and can be doped with polarization. A certain concentration of holes can be induced by gradually changing the components, i.e., at least one of g gradually decreasing and h gradually increasing along the metal-polar direction. Mg can also be doped during growth to produce conductive holes, and the distribution of the holes in the P-type confinement layer 70 is not required to be fixed.

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

[0067] Optionally, III-nitride films with higher Al components can 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 a carrier blocking effect.

[0068] Optionally, a transition layer, such as a superlattice, a medium-temperature layer, or the like, can be inserted between the buffer layer 20 and the N-type confinement layer 40, which is made of III-nitride materials. The transition layer can further filter material dislocations, release epitaxial stress, improve epitaxial morphology, and improve the crystal quality of the N-type confinement layer 40.

[0069] Step 120

[0070] After the epitaxial wafer 100 of the complete UV laser is obtained by epitaxial growth, a variable-power surface photoluminescence test 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, and 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, i.e., the surface of the epitaxial wafer 100 is excited, and the optical fiber 310 collects the luminescence spectrum from the front surface of the epitaxial wafer 100. The incident direction of the excitation light source can form a certain angle with the epitaxial wafer 100, and the angle range is not limited. For example, as shown in FIG. 3B, the optical fiber 310 is located on the normal direction of the epitaxial wafer 100, and can also be located on the left or right side of the normal direction. The collection direction of the luminescence spectrum forms a preset angle with the normal direction of the epitaxial wafer 100, i.e., the collection direction forms a certain angle with the normal direction, such as an angle θ, which is determined according to the detection of the low-energy peak, and the preset angle is preferably 0-60 degrees. Figure 3

[0073] ​The variable excitation power can directly adjust the output energy or voltage of the laser to realize variable power excitation, or a continuous or fixed attenuator can be used to realize variable power excitation by increasing or decreasing the attenuator at a larger output energy.

[0074] Step 130

[0075] The luminescence spectrum of the epitaxial wafer 100, in which a buffer layer 20 is first grown on a substrate 10, and then a quantum well active layer 30 is directly grown, is shown in FIG. 2. Figure 4 In FIG. 2, 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 at a higher excitation power, and the integral intensity and half-width of which need to be fitted.

[0076] The luminescence spectrum of the epitaxial wafer 100, in which a buffer layer 20 is first grown on a substrate 10, then an N-type confinement layer 40 and an N-type waveguide layer 50 are grown, then a quantum well active layer 30 is grown, and finally a P-type waveguide layer 60 is grown, is shown in FIG. 3. Figure 5 In FIG. 3, 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 at a higher excitation power, and the integral intensity and half-width of which need to be fitted.

[0077] The fitting function mainly adopts peak-type functions, such as Gauss, Gaussian, Lorentz, Laplace, Person VII, Person IV, etc., for single-peak or multi-peak fitting, so as to calculate the area and half-width of the narrow peak.

[0078] Step 140

[0079] The integral intensity of the quantum well low-energy end narrow peak is plotted against the excitation power to obtain a scatter plot, and linear fitting is performed to obtain the threshold at which the narrow peak appears.

[0080] Step 150

[0081] The threshold and the line width of the narrow peak of a plurality of epitaxial wafers 100 are compared, and based on the comparison result, the advantages and disadvantages of the lasing characteristics of the quantum well active layer 30 are predicted.

[0082] 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. The growth processes include growth temperature, growth rate, pressure, and five-to-three ratio, which represents the ratio of five-group source to three-group source, and the growth processes have an important influence on the advantages and disadvantages of the lasing characteristics of the quantum well active layer 30 of the epitaxial wafer 100.

[0083] The calculated starting threshold and line width of the epitaxial wafer 100 with smaller quantum well active layer 30 have better lasing characteristics. In the similar structure, the optical confinement ability is the same, and the smaller starting threshold and line width of the surface stimulated emission indicate that the internal loss is smaller. In the case of the same edge-emitting cavity surface loss, the epitaxial wafer 100 with smaller internal loss has better lasing characteristics. Thus, by comparing the starting threshold and line width of the narrow peak 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 integral intensity fitting scatter plot of the epitaxial wafer 100 with the same epitaxial structure grown by different dislocation density templates is shown. The line width of the epitaxial wafer 100 on the low dislocation density and high dislocation density templates is 1.22 nm and 1.68 nm, respectively. It can be seen that the starting threshold and line width of the epitaxial wafer 100 on the low dislocation density template are smaller.

[0085] In this embodiment, by testing the starting threshold and line width of the surface photostimulated emission of the epitaxial wafer 100, the advantages and disadvantages of the lasing characteristics of the quantum well active layer 30 of the ultraviolet laser can be quickly judged. The testing method is non-destructive testing, does not involve bar processing and chip preparation process, the operation process is simple, convenient and the testing result has good stability, which can effectively save the testing time and is beneficial to shorten the product development cycle.

[0086] Embodiment two

[0087] Step 110

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

[0089] The substrate 10 can be any one of sapphire, GaN, AlN, SiC and Si, and can also be extended to any substrate that can grow nitride. Preferably, the substrate 10 is light-transmitting on the back surface.

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

[0091] The material of the buffer layer 20 can be a single layer of a single component III-nitride material, such as AlN, GaN, AlGaN. The material of the 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 interlayer (such as graphene, hexagonal boron nitride, etc.), a superlattice transition layer, a high-temperature annealing layer, a homoepitaxial layer, and a high-temperature template layer, 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 confinement layer 40, which can be omitted or grown on the buffer layer 20. The N-type confinement layer 40 is made of a III-nitride material Al a In b Ga 1-a-b N, 0 < a < 1, 0 < b < 1, which can be a single component III-nitride material. Polar doping can be used to induce a certain concentration of electrons by means of composition grading, i.e., at least one of a gradually increasing and b gradually decreasing along the metal-polar direction. Si can also be doped during growth to produce conductive electrons, which have no fixed requirements for distribution in the N-type confinement layer 40. Si can also not be doped, as there is a certain background electron concentration under unintentional doping.

[0093] Optionally, the epitaxial wafer 100 further includes an N-type waveguide layer 50, which can be omitted or grown on the N-type confinement layer 40, and is located between the N-type confinement layer 40 and the quantum well active layer 30. The N-type waveguide layer 50 is made of a III-nitride material Al c In d Ga 1-c-d N, 0 < c < 1, 0 < d < 1, which has a smaller band gap than the N-type confinement layer 40. Si can be doped in this layer to suppress point defects, or Si can not be doped to reduce optical loss in the layer. The N-type waveguide layer 50 can be a single component III-nitride thin film material, or a composition grading layer with gradually increasing or decreasing band gap to induce free conductive electrons or further improve light confinement capability.

[0094] The quantum well active layer 30 can be a III-nitride double heterojunction structure, such as an Al x In y Ga 1-x-y N / Al x In y Ga 1-x-y N structure; or a single quantum well structure, such as a single layer of Al x In y Ga 1-x-y N structure; or a multi-quantum well structure, such as a multi-periodic Al x In y Ga1-x-y N / Al x In y Ga 1-x-y N structure, where 0 < x < 1, 0 < y < 1.

[0095] Optionally, the epitaxial wafer 100 further comprises a P-type waveguide layer 60, which can be omitted or grown on the quantum well active layer 30. It is made of III-nitride material Al e In f Ga 1-e-f N, 0 < e < 1, 0 < f < 1, and its band gap is preferably the same as that of the N-type confinement layer 40. This layer can be doped with Si to suppress point defects or undoped to reduce optical loss in the layer. The P-type waveguide layer 60 can be a single-component III-nitride thin film material, or a compositionally graded layer to induce free conducting holes or further improve light confinement capability. The composition of the P-type waveguide layer 60 is preferably the same as that of the N-type waveguide layer 50.

[0096] Optionally, the epitaxial wafer 100 further comprises a P-type confinement layer 70, which can be grown on the P-type waveguide layer 60. It is made of III-nitride material Al g In h Ga 1-g-h N, 0 < g < 1, 0 < h < 1, and can be a single-component III-nitride thin film. Polar doping can be used to induce a certain concentration of holes by compositionally grading, i.e., at least one of g gradually decreasing and h gradually increasing along the metal-polar direction. Mg can also be doped during growth to produce conducting holes, which have no fixed requirements for distribution in the P-type confinement layer 70.

[0097] Optionally, the epitaxial wafer 100 further comprises a P-type contact layer, which can be grown 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, III-nitride thin films with higher Al composition can 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.

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

[0100] Step 120

[0101] After obtaining the complete ultraviolet laser epitaxial wafer 100 through epitaxial growth, variable-power surface photoluminescence testing can be performed without any further 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 source and the acquisition direction of the emission spectrum are on opposite sides of the epitaxial wafer 100, i.e., on the surface of the epitaxial wafer 100. The optical fiber 310 acquires the emission spectrum from the back side of the epitaxial wafer 100. The incident direction of the excitation source can maintain a certain angle with the epitaxial wafer 100, and the angle range is unlimited. Figure 7 As shown, the optical fiber 310 is located in the normal direction of the epitaxial wafer 100, or it can be located to the left or right of the normal direction. The acquisition direction of the emission spectrum is at a preset angle to the normal direction of the epitaxial wafer 100, that is, the acquisition direction maintains a certain angle with the normal direction, as shown by angle θ, with the aim of detecting low energy peaks. The preferred range of the preset angle is 0 to 60 degrees.

[0103] Variable excitation power can be achieved by directly adjusting the output energy or voltage of the laser; alternatively, continuous or fixed attenuators can be used to achieve variable excitation at higher output energies by adding or removing attenuators.

[0104] Step 130

[0105] The emission spectrum of the epitaxial wafer 100, on substrate 10, is as follows: First, a buffer layer 20 is grown, then a quantum well active layer 30 is directly grown. Figure 4 As shown in the figure. Peak 1 corresponds to the emission peak of the active layer 30 of the quantum well, while peak 2 is a narrow peak at the low energy end generated under higher excitation power, and its integral intensity and full width at half maximum (FWHM) need to be fitted.

[0106] On substrate 10, a buffer layer 20 is first grown, followed by an N-type confinement layer 40 and an N-type waveguide layer 50, then a quantum well active layer 30, and finally a P-type waveguide layer 60. The emission spectrum of the epitaxial wafer 100 is as follows: Figure 5 As shown in the figure. Peak 1 corresponds to the emission peak of the P-type waveguide layer 60, peak 2 corresponds to the emission peak of the quantum well active layer 30, and peak 3 is a narrow peak at the low energy end generated under higher excitation power, which needs to be fitted with its integral intensity and full width at half maximum (FWHM).

[0107] The fitting function mainly adopts peak-type functions, such as Gaussian, Lorentz, Laplace, Person VII, and Person IV, etc., to perform single-peak or multi-peak fitting, and can fit and calculate the area and half-width of narrow peaks.

[0108] Step 140

[0109] The integral intensity of the narrow peak of the low-energy end of the quantum well is plotted against the excitation power, and linear fitting is performed to obtain the threshold value at which the narrow peak appears.

[0110] Step 150

[0111] The threshold value and the line width of the narrow peak of the plurality of epitaxial wafers 100 are compared, and based on the comparison result, the advantages and disadvantages of the lasing characteristics of the quantum well active layer 30 are predicted. The plurality of epitaxial wafers 100 are formed under different growth processes, and the composition and thickness of each layer of each epitaxial wafer 100 are the same.

[0112] The epitaxial wafer 100 with the calculated threshold value and line width of the narrow peak is smaller, and the lasing characteristics of the quantum well active layer 30 thereof are better. Under similar structures, the optical confinement capability is the same, and the smaller the threshold value and the line width of the surface stimulated emission, the smaller the internal loss. Under the same edge-emitting cavity surface loss, the epitaxial wafer 100 with smaller internal loss has better lasing characteristics. Thus, by comparing the threshold value and the line width of the narrow peak of the plurality of 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 fitting scatter plot of the integral intensity of the narrow peak of the epitaxial wafer 100 grown using templates with different dislocation densities and the same epitaxial structure is shown. The line width of the epitaxial wafer 100 on the low-dislocation-density template and the high-dislocation-density template is 1.22 nm and 1.68 nm, respectively. It can be seen that the threshold value and the line width of the epitaxial wafer 100 on the low-dislocation-density template are smaller.

[0114] Example Three

[0115] Step 110

[0116] As shown in Figure 8 , 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 on the substrate 10 from bottom to top to obtain a complete epitaxial wafer 100 of the ultraviolet light-emitting diode.

[0117] The substrate 10 can be any one of sapphire, GaN, AlN, SiC, and Si, and can also be extended to any substrate 10 that can grow nitride. Preferably, the substrate 10 is light-transmitting on the back surface.

[0118] The buffer layer 20 can be a single-layer single-component III-nitride material such as AlN, GaN, and AlGaN. The material of the 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 a two-dimensional insertion layer such as graphene and hexagonal boron nitride), a superlattice transition layer, a high-temperature annealing layer, a homoepitaxial layer, and a high-temperature template layer, to improve the quality of the epitaxial layer and enhance the optical confinement capability.

[0119] Optionally, the epitaxial wafer 100 further comprises an N-type layer 80 grown on the buffer layer 20 between the buffer layer 20 and the quantum well active layer 30. The N-type layer 80 is made of III-nitride material Al j In k Ga 1-j-k N, 0 < j < 1, 0 < k < 1, which can be a single component III-nitride film; polar doping can be used to induce a certain concentration of electrons by means of composition grading, i.e. at least one of j gradually increasing and k gradually decreasing along the metal-polar direction. Si can also be doped during growth to produce conductive electrons, which have no fixed requirement for distribution in the N-type confinement layer 40. Si can also not be doped, because there is a certain background electron concentration under unintentional doping.

[0120] The quantum well active layer 30 can be a III-nitride double heterostructure: such as a thick Al m In n Ga 1-m-n N / Al m In n Ga 1-m-n N structure; or a single quantum well structure: such as a thin single-layer Al m In n Ga 1-m-n N structure; or a multiple quantum well structure: such as a thin multi-period Al m In n Ga 1-m-n N / Al m In n Ga 1-m-n N structure, where 0 < m < 1, 0 < n < 1.

[0121] Optionally, the epitaxial wafer 100 further comprises a P-type layer 90 grown on the quantum well active layer 30. The P-type layer 90 is made of III-nitride material Al p In q Ga 1-p-q N, 0 < p < 1, 0 < q < 1, which can be a single component III-nitride film; polar doping can be used to induce a certain concentration of holes by means of composition grading, i.e. at least one of p gradually decreasing and q gradually increasing along the metal-polar direction. Mg can also be doped during growth to produce conductive holes, which have no fixed requirement for distribution in the P-type confinement layer 70.

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

[0123] Optionally, 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, a III-nitride thin film with a higher Al composition can be grown to achieve a carrier blocking effect.

[0124] Optionally, a transition layer such as a superlattice, a medium temperature layer, etc. made of III-nitride material can 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 improve the crystal quality of the N-type layer 80.

[0125] Further, 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, as long as there is a thin film structure with a lower refractive index on both sides of the quantum well active layer 30.

[0126] Step 120

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

[0128] Further, as described in step 110, a quantum well active layer structure can also be obtained by electrochemical etching, two-dimensional material peeling, etc., as long as there is a thin film material with a lower refractive index on both 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, i.e. 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 form a certain angle with the epitaxial wafer 100, and the angle range is not limited. As shown in FIG. 11, the optical fiber 310 is located in the normal direction of the epitaxial wafer 100, and can also be located on the left or right side of the normal direction. The collection direction of the luminescence spectrum forms a preset angle with the normal direction of the epitaxial wafer 100, and the preset angle range is preferably 0-60 degrees. Figure 7

[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, i.e. 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 form a certain angle with the epitaxial wafer 100, and the angle range is not limited. As shown in FIG. 12, the optical fiber 310 is located in the normal direction of the epitaxial wafer 100, and can also be located on the left or right side of the normal direction. The collection direction of the luminescence spectrum forms a preset angle with the normal direction of the epitaxial wafer 100, and the preset angle range is preferably 0-60 degrees. Figure 3 ​As shown in the figure, the optical fiber 310 is located in the normal direction of the epitaxial wafer 100, and can also be located 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, and the preset angle is preferably 0-60 degrees.

[0131] The variable excitation power can directly adjust the output energy or voltage of the laser to realize variable power excitation, or a continuous or fixed attenuator can be used to realize variable power excitation by increasing or decreasing the attenuator at a larger output energy.

[0132] Step 130

[0133] Each obtained luminescence spectrum is subjected to single-peak or multi-peak function fitting to obtain the integral intensity and line width of the narrow peak at the low-energy end of the quantum well.

[0134] The fitting function mainly uses peak value type functions, such as Gauss, Gaussian, Lorentz, Laplace, Person VII, Person IV, etc., for single-peak or multi-peak fitting, so as to calculate the area and half-width of the narrow peak.

[0135] Step 140

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

[0137] Step 150

[0138] The starting threshold and line width of the narrow peak of a plurality of epitaxial wafers 100 are compared, and based on the comparison result, the advantages and disadvantages of the luminescence characteristics of the quantum well active layer 30 are predicted.

[0139] A 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. The growth processes include growth temperature, growth rate, pressure, and V / III ratio, and the growth processes have an important influence on the advantages and disadvantages of the luminescence 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 surface stimulated emission starting threshold and line width, the smaller the internal loss, and the quantum well active layer 30 has better luminescence characteristics.

[0141] Figure 6The narrow peak integral intensity fitting scatter plot of the epitaxial wafer 100 using different dislocation density templates to grow the same epitaxial structure is shown. The line width of the epitaxial wafer 100 on the low dislocation density and high dislocation density templates is 1.22 nm and 1.68 nm, 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 the present embodiment, by testing the starting threshold and line width of the surface photostimulated emission of the epitaxial wafer 100, the advantages and disadvantages of the light emitting 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, does not involve bar processing and chip preparation process, the operation process is simple and the testing result has good stability, can effectively save the testing time, and is conducive to shortening the research and development cycle of the product.

[0143] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions made within the spirit and principles of the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A test method for determining the lasing characteristics of a quantum well active layer, characterized by, The method comprises the following steps: selecting a substrate, sequentially growing a buffer layer and a quantum well active layer on the substrate to obtain an epitaxial wafer; performing a surface photoluminescence test with variable excitation power on the epitaxial wafer to collect luminescence spectra; performing single-peak or multi-peak function fitting on each of the obtained luminescence spectra to obtain the integral intensity and line width of the narrow peak at the low-energy end of the quantum well; plotting 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 obtaining the threshold value at which the narrow peak appears through linear fitting; comparing the threshold value and the line width of the narrow peak of a plurality of epitaxial wafers, and predicting the lasing characteristics of the quantum well active layer based on the comparison result; the epitaxial wafer in the test method has not been subjected to cleavage treatment, and the test performed on the epitaxial wafer is a non-destructive test.

2. The test method of claim 1, wherein the step of performing a surface photoluminescence test with variable excitation power on the epitaxial wafer to collect luminescence spectra 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 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 on opposite sides of the epitaxial wafer.

3. The test method of claim 2, wherein the collection direction of the luminescence spectrum and the normal direction of the epitaxial wafer form a preset angle, and the preset angle ranges from 0 to 60 degrees.

4. The test method of claim 1, wherein the step of obtaining an epitaxial wafer further comprises: the epitaxial wafer further comprises an N-type confinement layer and an N-type waveguide layer, and 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 comprises 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 test method of claim 4, wherein the step of obtaining an epitaxial wafer further comprises: the epitaxial wafer further comprises a P-type contact layer, and the P-type contact layer is grown on the P-type confinement layer; and / or the epitaxial wafer further comprises a transition layer, and the transition layer is grown between the buffer layer and the N-type confinement layer.

6. The test method of claim 1, wherein the step of obtaining an epitaxial wafer further comprises: the epitaxial wafer further comprises an N-type layer and a P-type layer, and 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 test method of claim 6, wherein the step of obtaining an epitaxial wafer further comprises: the epitaxial wafer further comprises a P-type contact layer, and the P-type contact layer is grown on the P-type layer; and / or the epitaxial wafer further comprises a transition layer, and the transition layer is grown between the buffer layer and the N-type layer.

8. The test method of any one of claims 1-7, wherein the material of the substrate comprises any one of sapphire, GaN, AlN, SiC, and Si.

9. The test method of any one of claims 1-7, wherein, the structure of the quantum well active layer comprises any one of a double heterostructure, a single quantum well structure, and a multiple quantum well structure.

10. The test method of any one of claims 1-7, wherein, the process parameters for the epitaxial wafer growth comprise a growth temperature, a growth rate, a pressure, and a V / III ratio.

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