A positive polarity infrared LED epitaxial structure and preparation method thereof

Abstract

The present invention relates to the technical field of semiconductor materials and discloses an epitaxial structure of a positive-polarity infrared LED and a preparation method thereof. The epitaxial structure comprises a buffer layer, an N-AlGaAs current spreading layer, an N-AlGaAs confinement layer, a multi-quantum well layer, a P-AlGaAs confinement layer, a P-AlGaAs current spreading layer, and a P-type GaAs ohmic contact layer, which are sequentially stacked. The P-AlGaAs current spreading layer is a superlattice formed by periodically alternating stacking of C-doped AlGaAs layers and Mg-doped AlGaAs layers. This structure facilitates more uniform distribution of holes in the epitaxial layer, grows a high-quality, highly uniform epitaxial layer, improves the yield of the LED chip, reduces light absorption, and effectively improves luminous efficiency and luminous intensity.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor materials, and in particular to an epitaxial structure of a positive-polarity infrared LED and a preparation method thereof. Background Art

[0002] Infrared LEDs are near-infrared light-emitting devices that convert electrical energy into light. Their wavelengths are concentrated in the 1μm-3μm range. They offer a range of advantages, including compact size, low power consumption, long life, high stability, and good directivity. Currently, infrared LEDs are widely used in remote control, telemetry, optical isolation, optical switching, photoelectric control, and target tracking systems.

[0003] In the prior art, the P-type layer material in the epitaxial structure of positive-polarity infrared LEDs is AlGaAs, doped with Mg or C. However, the following defects still exist: Mg doping reduces the window for epitaxial growth, making Mg-induced epitaxial defects more likely to occur, and resulting in severe light absorption. C doping places high demands on reaction chamber temperature and airflow. For example, when growing C-doped epitaxial layers in an Aixtron-G4-15 chip processing device, the C doping content on the flat edge is easily 1-2 times higher than that on the round edge due to the large size of the small disk and water cooling of the edge sidewalls, resulting in significant differences in electrical properties within the chip. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an epitaxial structure of a positive polarity infrared LED and a preparation method thereof, which can reduce the light absorption of the P-type layer, make the hole concentration in the epitaxial wafer uniform, and improve the crystal quality of the epitaxial layer.

[0005] In order to solve the above technical problems, the first aspect of the present invention provides an epitaxial structure of a positive polarity infrared LED, characterized in that it includes a buffer layer, an N-AlGaAs current spreading layer, an N-AlGaAs confinement layer, a multi-quantum well layer, a P-AlGaAs confinement layer, a P-AlGaAs current spreading layer, and a P-type GaAs ohmic contact layer stacked in sequence;

[0006] The P-AlGaAs current spreading layer is a superlattice formed by periodically alternating stacking of C-doped AlGaAs layers and Mg-doped AlGaAs layers, with the number of periods being 33 to 150. In each period, the C-doped AlGaAs layer is located below the Mg-doped AlGaAs layer.

[0007] As an improvement of the above solution, the total thickness of the P-AlGaAs current spreading layer is 4 μm to 9 μm.

[0008] As an improvement of the above solution, the thickness of the C-doped AlGaAs layer is 30 nm to 60 nm, and the thickness of the Mg-doped AlGaAs layer is 30 nm to 60 nm.

[0009] As an improvement to the above solution, the hole solubility in the P-AlGaAs current spreading layer is greater than 3.5×10 18 cm -3 , the doping amount of the C-doped AlGaAs layer is less than the doping amount of the Mg-doped AlGaAs layer.

[0010] As an improvement to the above solution, the C doping amount in the C-doped AlGaAs layer is 3×10 18 cm -3 ~4×10 18 cm -3 ;

[0011] The doping amount of Mg in the Mg-doped AlGaAs layer is 3.5×10 18 cm -3 ~4.5×10 18 cm -3 .

[0012] As an improvement to the above solution, the Al content in the C-doped AlGaAs layer is 0.1 to 0.4;

[0013] The Al content in the Mg-doped AlGaAs layer is 0.1-0.4.

[0014] As an improvement to the above solution, the growth temperature of the C-doped AlGaAs layer is 650° C. to 720° C., and the growth pressure is 30 to 80 mbar;

[0015] The growth temperature of the Mg-doped AlGaAs layer is 650° C. to 720° C., and the growth pressure is 30 to 80 mbar.

[0016] As an improvement to the above solution, the Mg-doped AlGaAs layer is annealed after growth, and then the next cycle of C-doped AlGaAs layer is grown. The annealing process is: maintaining the temperature at 650° C. to 720° C. for 5 seconds to 10 seconds.

[0017] The second aspect of the present invention further provides a method for preparing the epitaxial structure of the positive polarity infrared LED, comprising:

[0018] growing a buffer layer on the substrate;

[0019] Growing an N-AlGaAs current spreading layer on the buffer layer;

[0020] growing an N-AlGaAs confinement layer on the N-AlGaAs current spreading layer;

[0021] Growing a multi-quantum well layer on the N-AlGaAs confinement layer;

[0022] Growing a P-AlGaAs confinement layer on the multi-quantum well layer;

[0023] growing a P-AlGaAs current spreading layer on the P-AlGaAs confinement layer;

[0024] Growing a P-type GaAs ohmic contact layer on the P-AlGaAs current spreading layer;

[0025] The P-AlGaAs current spreading layer is a superlattice formed by periodically alternating stacking of C-doped AlGaAs layers and Mg-doped AlGaAs layers, wherein in each cycle, the C-doped AlGaAs layer is located below the Mg-doped AlGaAs layer;

[0026] As an improvement to the above solution, growing a P-AlGaAs current spreading layer on the P-AlGaAs confinement layer includes:

[0027] (1) controlling the temperature of the reaction chamber to be maintained at 650° C. to 720° C., and growing a C-doped AlGaAs layer using a C source, an Al source, a Ga source, and an As source;

[0028] (2) Turn off the C source, introduce the Mg source, Al source, Ga source, and As source to grow the Mg-doped AlGaAs layer, completing one cycle of growth;

[0029] (3) Turn off the Group III source and Mg source, maintain the temperature and perform annealing for 5s to 10s;

[0030] (4) Repeat steps (1) to (3) until the thickness or the number of cycles reaches the preset value.

[0031] The implementation of the present invention has the following beneficial effects:

[0032] In the present invention, a P-AlGaAs current spreading layer is provided on a P-AlGaAs confinement layer and a P-type GaAs ohmic contact layer, and the P-AlGaAs current spreading layer is a superlattice formed by periodically and alternately stacking a C-doped AlGaAs layer and a Mg-doped AlGaAs layer. Compared with a traditional Mg-doped structure, it is easier to grow a high-quality epitaxial layer, with fewer epitaxial defects, and the light absorption of C-doping is less than that of Mg-doping, which can effectively improve the epitaxial luminescence efficiency. Compared with a traditional C-doped structure, it is easier to grow highly uniform P-AlGaAs, and the electrical uniformity within the chip is greatly improved compared with single C-doping, thereby improving the luminous intensity.

[0033] The present invention adopts a cyclic annealing method to allow Mg doping to diffuse in the C-doped AlGaAs layer, so that the C-doped AlGaAs layer, which is very sensitive to temperature, has better hole solubility uniformity due to the diffusion of Mg doping, greatly improving the electrical yield within the chip and further improving the yield of the epitaxial wafer. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 : A schematic structural diagram of an epitaxial structure of a positive polarity infrared LED in the present invention;

[0035] Figure 2 : A method for preparing an epitaxial structure of a positive polarity infrared LED in the present invention;

[0036] Figure 3 : Schematic diagram of the flow rate of Al source, Ga source, C source and Mg source in steps (1) to (3) of Example 1 of the present invention (source amount of MO source).

[0037] Reference numerals:

[0038] 1-buffer layer; 2-N-AlGaAs current spreading layer; 3-N-AlGaAs confinement layer; 4-multiple quantum well layer; 5-P-AlGaAs confinement layer; 6-P-AlGaAs current spreading layer; 61-C-doped AlGaAs layer; 62-Mg-doped AlGaAs layer; 7-P-type GaAs ohmic contact layer. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail with reference to specific embodiments below.

[0040] In order to solve the above problems, the first aspect of the present invention provides an epitaxial structure of a positive polarity infrared LED, see Figure 1 , including a buffer layer 1, an N-AlGaAs current spreading layer 2, an N-AlGaAs confinement layer 3, a multi-quantum well layer 4, a P-AlGaAs confinement layer 5, a P-AlGaAs current spreading layer 6, and a P-type GaAs ohmic contact layer 7 stacked in sequence;

[0041] The P-AlGaAs current spreading layer 6 is a superlattice formed by periodically alternating stacking of C-doped AlGaAs layers 61 and Mg-doped AlGaAs layers 62, with the number of periods being 33 to 150. In each period, the C-doped AlGaAs layer 61 is located below the Mg-doped AlGaAs layer 62.

[0042] In 3×10 18 cm -3Among the above high-solubility impurity semiconductors, the Mg-doped AlGaAs epitaxial layer has more defects when it is thicker. In the present invention, a structure in which C-doped AlGaAs layers 61 and Mg-doped AlGaAs layers 62 are periodically alternately stacked is adopted. Through periodic annealing, the Mg element can be uniformly diffused in the AlGaAs epitaxial layer, which can increase the hole concentration and achieve the ideal high doping. At the same time, a higher-quality AlGaAs epitaxial layer is obtained, which has fewer surface defects on the epitaxial layer and higher light extraction efficiency of the LED.

[0043] Preferably, the hole solubility in the P-AlGaAs current spreading layer 6 is greater than 3.5×10 18 cm -3 The doping amount of the C-doped AlGaAs layer 61 is less than the doping amount of the Mg-doped AlGaAs layer 62, which is beneficial to the diffusion of the Mg element, can effectively reduce the ionization energy of the Mg impurities, and can regulate the defect state in the material, increase the hole concentration of the doping layer, and thus improve the efficiency of p-type doping.

[0044] Furthermore, the Al content in the C-doped AlGaAs layer 61 is 0.1-0.4, and the C doping amount is 3×10 18 cm -3 ~4×10 18 cm -3 , an exemplary doping level is 3×10 18 cm -3 , 3.2×10 18 cm -3 , 3.4×10 18 cm -3 , 3.6×10 18 cm -3 , 3.8×10 19 cm -3 , 4×10 18 cm -3 , but not limited thereto; the Al component of the Mg-doped AlGaAs layer 62 is 0.1 to 0.4, and the Mg doping amount is 3.5×10 18 cm -3 ~4.5×10 18 cm -3 , an exemplary doping level is 3.5×10 18 cm -3 , 3.7×10 18 cm -3 , 3.9×10 18 cm -3 , 4.1×10 18 cm -3 , 4.3×10 18 cm-3 , 4.5×10 18 cm -3 , but not limited to this.

[0045] Preferably, the exemplary period numbers in the present invention are 33, 35, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, and 150, but are not limited thereto. The total thickness of the P-AlGaAs current spreading layer 6 is 4 μm to 9 μm, and exemplary ones are 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, and 9 μm, but are not limited thereto. Controlling the thickness of the P-AlGaAs current spreading layer 6 to be 4 μm to 9 μm can evenly distribute the injected carriers to the active region, reduce the carrier crowding effect, and thus improve the luminous efficiency and uniformity of the LED. If the thickness is too high, the crystal quality of the Mg-doped AlGaAs layer 62 will be reduced, and the carriers will spread too far, affecting the luminous efficiency.

[0046] Furthermore, the thickness of the C-doped AlGaAs layer 61 is 30 nm to 60 nm, with exemplary thicknesses of 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, and 60 nm, but not limited thereto; the thickness of the Mg-doped AlGaAs layer 62 is 30 nm to 60 nm, with exemplary thicknesses of 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, and 60 nm, but not limited thereto.

[0047] Furthermore, after the Mg-doped AlGaAs layer 62 is grown, it is annealed, and then the next cycle of C-doped AlGaAs layer 61 is grown. The annealing process is performed by maintaining the temperature at 650°C to 720°C for 5 to 10 seconds. By using a cyclic annealing method, the Mg doped in the Mg-doped AlGaAs layer 62 diffuses into the C-doped AlGaAs layer 61. This makes the C-doped AlGaAs layer 61, which is very sensitive to temperature, more uniform in terms of hole solubility within the wafer due to the diffusion of Mg doping, and the electrical yield within the wafer is greatly improved.

[0048] Correspondingly, the present invention also provides a method for preparing the epitaxial structure of a positive polarity infrared LED, see Figure 2 ,include:

[0049] S01, growing a buffer layer 1 on a substrate;

[0050] In the present invention, the epitaxial structure of a positive-polarity infrared LED is deposited and grown in an MOCVD device. Before growing the buffer layer 1, pretreatment is required. The pretreatment includes: adjusting the pressure of the reaction chamber, introducing hydrogen and arsine, adjusting the temperature in the reaction chamber, and performing a baking treatment. The introduction of hydrogen and arsine can clean the substrate surface and remove oxides and other contaminants on the substrate surface. The pressure in the reaction chamber is maintained at a low pressure, which is 30 mbar to 70 mbar, preferably 50 mbar.

[0051] Furthermore, the temperature of the reaction chamber is adjusted to 730°C to 78°C for a baking treatment of 3 minutes to 8 minutes. The baking treatment can reduce defects in the material, promote the migration and reaction of atoms on the substrate surface, thereby increasing the growth rate and improving the interface quality between the epitaxial structure and the substrate.

[0052] The type of substrate in the present invention is not limited and may be a silicon substrate, a GaAs substrate, etc., which are not marked in the figure.

[0053] Preferably, the buffer layer 1 is a GaAs buffer layer 1 , and the thickness of the buffer layer 1 is 100 nm to 400 nm.

[0054] Furthermore, the buffer layer 1 is a Si-doped GaAs buffer layer 1, and the Si doping amount is 1×10 18 cm -3 ~2×10 18 cm -3 .

[0055] Furthermore, the growth temperature of the buffer layer 1 is 650° C. to 720° C., and the growth pressure is 30 mbar to 70 mbar.

[0056] S02, growing an N-AlGaAs current spreading layer 2 on the buffer layer 1;

[0057] Preferably, the doping element of the N-AlGaAs current spreading layer 2 is Si, and the doping amount of Si is 1×10 18 cm -3 ~4×10 18 cm -3 The thickness of the N-AlGaAs current spreading layer 2 is 0.2 μm to 3 μm.

[0058] Furthermore, the growth temperature of the N-AlGaAs current spreading layer 2 is 650° C. to 720° C., and the growth pressure is 30 mbar to 70 mbar.

[0059] S03, growing an N-AlGaAs confinement layer 3 on the N-AlGaAs current spreading layer 2;

[0060] Preferably, the doping element of the N-AlGaAs confinement layer 3 is Si, and the doping amount of Si is 1×10 18 cm -3 ~4×10 18 cm -3 The thickness of the N-AlGaAs current spreading layer 2 is 100nm to 500nm.

[0061] Furthermore, the growth temperature of the N-AlGaAs confinement layer 3 is 650° C. to 720° C., and the growth pressure is 30 mbar to 70 mbar.

[0062] S04, growing a multi-quantum well layer 4 on the N-AlGaAs confinement layer 3;

[0063] Preferably, the multi-quantum well layer 4 is a periodic structure of alternating stacking of InGaAs quantum well layers and AlGaAs quantum barrier layers, with a period number of 4 to 30. The In component of the InGaAs quantum well layer is 0.1 to 0.15, and the thickness is 5 nm to 10 nm; the Al component of the AlGaAs quantum barrier layer is 0.02 to 0.1, and the thickness is 10 nm to 30 nm.

[0064] Furthermore, the growth temperature of the InGaAs quantum well layer and the AlGaAs quantum barrier layer are both 650° C. to 680° C., and the growth pressure is 30 mbar to 70 mbar.

[0065] S05, growing a P-AlGaAs confinement layer 5 on the multi-quantum well layer 4;

[0066] Preferably, the doping element of the P-AlGaAs confinement layer 5 is C, and the doping amount of C is 2×10 18 cm -3 ~4×10 18 cm -3 The thickness of the P-AlGaAs confinement layer 5 is 100 nm to 500 nm.

[0067] Furthermore, the growth temperature of the N-AlGaAs current spreading layer 2 is 650° C. to 720° C., and the growth pressure is 30 mbar to 70 mbar.

[0068] S06, growing a P-AlGaAs current spreading layer 6 on the P-AlGaAs confinement layer 5;

[0069] Preferably, the growth temperature of the C-doped AlGaAs layer 61 is 650°C to 720°C, exemplarily 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, and 720°C, but not limited thereto; the growth pressure is 30 to 80 mbar, exemplarily 30 mbar, 40 mbar, 50 mbar, 60 mbar, 70 mbar, and 80 mbar, but not limited thereto. The growth temperature of the Mg-doped AlGaAs layer 62 is 650°C to 720°C, exemplarily 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, and 720°C, but not limited thereto; the growth pressure is 30 to 80 mbar, exemplarily 30 mbar, 40 mbar, 50 mbar, 60 mbar, 70 mbar, and 80 mbar, but not limited thereto.

[0070] Furthermore, when growing the C-doped AlGaAs layer 61, the ratio of the flow rates of the Al source and the C source in the C-doped AlGaAs layer 61 is 1:(0.23-0.28), exemplarily 1:0.23, 1:0.24, 1:0.25, 1:0.26, 1:0.27, 1:0.28, but not limited thereto. When growing the Mg-doped AlGaAs layer 62, the ratio of the flow rates of the Al source and the C source is 1:(0.3-0.35), exemplarily 1:0.3, 1:0.31, 1:0.32, 1:0.33, 1:0.34, 1:0.35, but not limited thereto. Controlling the Al source and the doping element C source or Mg source when growing the C-doped AlGaAs layer 61 or the Mg-doped AlGaAs layer 62 is beneficial to promoting the uniformity of the P-AlGaAs current spreading layer 6, ensuring the addition of sufficient doping elements, and increasing the hole concentration as much as possible.

[0071] Furthermore, after the Mg-doped AlGaAs layer 62 is grown, it is annealed, and then the next cycle of C-doped AlGaAs layer 61 is grown. The annealing process is performed by maintaining the temperature at 650°C to 720°C for 5 to 10 seconds. By using a cyclic annealing method, the Mg doped in the Mg-doped AlGaAs layer 62 diffuses into the C-doped AlGaAs layer 61. This makes the C-doped AlGaAs layer 61, which is very sensitive to temperature, more uniform in terms of hole solubility within the wafer due to the diffusion of Mg doping, and the electrical yield within the wafer is greatly improved.

[0072] In some specific and preferred embodiments, step S06 includes:

[0073] (1) Controlling the temperature of the reaction chamber to be maintained at 650° C. to 720° C., and growing a C-doped AlGaAs layer 61 using a C source, an Al source, a Ga source, and an As source;

[0074] (2) Turn off the C source, and introduce the Mg source, Al source, Ga source, and As source to grow the Mg-doped AlGaAs layer 62, completing one cycle of growth;

[0075] (3) Turn off the Group III source and Mg source, maintain the temperature and perform annealing for 5s to 10s;

[0076] (4) Repeat steps (1) to (3) until the thickness or the number of cycles reaches the preset value.

[0077] S07 . Growing a P-type GaAs ohmic contact layer 7 on the P-AlGaAs current spreading layer 6 .

[0078] Preferably, the doping element of the P-type GaAs ohmic contact layer 7 is C, and the doping amount of C is 7×10 19 cm -3 ~2×10 20 cm -3 The thickness of the P-type GaAs ohmic contact layer 7 is 30 nm to 150 nm.

[0079] Furthermore, the growth temperature of the P-type GaAs ohmic contact layer 7 is 580° C. to 630° C., and the growth pressure is 30 mbar to 70 mbar.

[0080] It should be noted that high-purity H2 (hydrogen) is used as the carrier gas, the As source is AsH (arsine), the N source is high-purity NH3, the Al source is TMAl (trimethylaluminum), the Ga source is TMGa (trimethylgallium), the In source is TMIn (trimethylindium), the Si source is SiH4, and the Mg source is CP2Mg.

[0081] The present invention will be further described below with specific embodiments:

[0082] Example 1

[0083] This embodiment provides an epitaxial structure of a positive polarity infrared LED, comprising a buffer layer, an N-AlGaAs current spreading layer, an N-AlGaAs confinement layer, a multi-quantum well layer, a P-AlGaAs confinement layer, a P-AlGaAs current spreading layer, and a P-type GaAs ohmic contact layer stacked in sequence.

[0084] The P-AlGaAs current spreading layer is a superlattice formed by periodically alternating stacking of C-doped AlGaAs layers and Mg-doped AlGaAs layers. In each period, the C-doped AlGaAs layer is located below the Mg-doped AlGaAs layer.

[0085] The Al composition of the C-doped AlGaAs layer is 0.25, and the C doping amount is 3.0×10 18 cm-3 , with a thickness of 45 nm; the Al composition of the Mg-doped AlGaAs layer is 0.25, and the Mg doping amount is 4.0×10 18 cm -3 , thickness is 50nm, number of periods is 53, and total thickness is 5.035μm.

[0086] The hole solubility in the P-AlGaAs current spreading layer is 3.5×10 18 cm -3 .

[0087] It is prepared by the following preparation method:

[0088] S01. In the MOCVD equipment, maintain a low pressure of 50 mbar, introduce hydrogen and arsine, increase the temperature to 750°C, bake at high temperature for 5 minutes, and then grow a buffer layer on the substrate;

[0089] The buffer layer is a Si-doped GaAs buffer layer with a Si doping amount of 1.5×10 18 cm -3 .

[0090] Specifically, the temperature was lowered to 690° C., and Ga source, As source, and Si source were introduced to grow a Si-doped GaAs buffer layer with a thickness of 250 nm.

[0091] S02, growing N-AlGaAs current spreading layer on the buffer layer

[0092] The doping element of the N-AlGaAs current spreading layer is Si, and the doping amount of Si is 2.5×10 18 cm -3 .

[0093] Specifically, the temperature was maintained at 690° C., and Ga source, Al source, As source, and Si source were introduced to grow an N-AlGaAs current spreading layer with a thickness of 1.5 μm.

[0094] S03, growing an N-AlGaAs confinement layer on the N-AlGaAs current spreading layer

[0095] The doping element of the N-AlGaAs confinement layer is Si, and the doping amount of Si is 3×10 18 cm -3 .

[0096] Specifically, the temperature was maintained at 690° C., and Ga source, Al source, As source, and Si source were introduced to grow an N-AlGaAs confinement layer with a thickness of 300 nm.

[0097] S04. Growing a multi-quantum well layer on the N-AlGaAs confinement layer

[0098] The multi-quantum well layer is a periodic structure of alternately stacked InGaAs quantum well layers and AlGaAs quantum barrier layers, with a period number of 15. The In component of the InGaAs quantum well layer is 0.12 and the thickness is 7nm; the Al component of the AlGaAs quantum barrier layer is 0.05 and the thickness is 20nm.

[0099] Specifically, the temperature was lowered to 665°C, and Ga source, In source, and As source were introduced to grow the InGaAs quantum well layer. Subsequently, the In source was turned off, and Ga source, Al source, and As source were introduced to grow the AlGaAs quantum barrier layer to complete one cycle of growth. Subsequently, the quantum well layer and quantum barrier layer were repeatedly stacked and grown for 14 cycles.

[0100] S05. Growing a P-AlGaAs confinement layer on the multi-quantum well layer

[0101] The doping element of the P-AlGaAs confinement layer is C, and the doping amount of C is 3×10 18 cm -3 , with a thickness of 300nm.

[0102] Specifically, the temperature was raised to 690° C., and Ga source, Al source, As source, and C source were introduced to grow a P-AlGaAs confinement layer.

[0103] S06, growing a P-AlGaAs current spreading layer on the P-AlGaAs confinement layer;

[0104] The P-AlGaAs current spreading layer is a superlattice formed by periodically alternating stacking of C-doped AlGaAs layers and Mg-doped AlGaAs layers. In each period, the C-doped AlGaAs layer is located below the Mg-doped AlGaAs layer.

[0105] Specifically:

[0106] (1) The temperature is maintained at 690°C, and a C-doped AlGaAs layer is grown using a C source, an Al source, a Ga source, and an As source;

[0107] (2) Turn off the C source, introduce the Mg source, Al source, Ga source, and As source to grow the Mg-doped AlGaAs layer, completing one cycle of growth;

[0108] (3) Turn off the Group III source and Mg source, maintain the temperature and perform annealing for 8 seconds;

[0109] (4) Repeat steps (1) to (3) 52 times to complete the growth of the P-AlGaAs current spreading layer.

[0110] The flow rates of Al source, Ga source, C source and Mg source in steps (1) to (3) are as follows: Figure 3As shown (since the saturated vapor pressure of Al is lower than that of Ga, the source flow rate must be much larger to be consistent with the mol amount of the Ga source).

[0111] S07. Growing a P-type GaAs ohmic contact layer on the P-AlGaAs current spreading layer.

[0112] The doping element of the P-type GaAs ohmic contact layer is C, and the doping amount of C is 7×10 19 cm -3 ~2×10 20 cm -3 The thickness of the P-type GaAs ohmic contact layer is 30nm to 150nm.

[0113] Specifically, the temperature was lowered to 600° C., and a C source, a Ga source, and an As source were introduced to grow a P-type GaAs ohmic contact layer with a thickness of 90 nm.

[0114] Example 2

[0115] This embodiment provides an epitaxial structure of a positive-polarity infrared LED, which is basically the same as that of the first embodiment, except that:

[0116] The Al composition of the C-doped AlGaAs layer is 0.25, and the C doping amount is 3.5×10 18 cm -3 The Al composition of the Mg-doped AlGaAs layer is 0.25, and the Mg doping amount is 4.5×10 18 cm -3 .

[0117] Example 3

[0118] This embodiment provides an epitaxial structure of a positive-polarity infrared LED, which is basically the same as that of the first embodiment, except that:

[0119] The thickness of the C-doped AlGaAs layer is 30 nm; the thickness of the Mg-doped AlGaAs layer is 60 nm.

[0120] Example 4

[0121] This embodiment provides an epitaxial structure of a positive-polarity infrared LED, which is basically the same as that of the first embodiment, except that:

[0122] In S06 of the preparation method, the next cycle of growth is performed without undergoing cyclic annealing treatment.

[0123] Specifically:

[0124] (1) The temperature is maintained at 690°C, and a C-doped AlGaAs layer is grown using a C source, an Al source, a Ga source, and an As source;

[0125] (2) Turn off the C source, introduce the Mg source, Al source, Ga source, and As source to grow the Mg-doped AlGaAs layer, completing one cycle of growth;

[0126] (3) Repeat steps (1) to (2) 52 times to complete the growth of the P-AlGaAs current spreading layer.

[0127] Comparative Example 1

[0128] This comparative example provides an epitaxial structure of a positive polarity infrared LED, which is basically the same as that of Example 1, except that:

[0129] The P-AlGaAs current spreading layer is a C-doped AlGaAs layer with a thickness of 5.035 μm and a C doping amount of 3.5×10 18 cm -3 , the hole solubility is 3.5×10 18 cm -3 .

[0130] Comparative Example 2

[0131] This comparative example provides an epitaxial structure of a positive polarity infrared LED, which is basically the same as that of Example 1, except that:

[0132] The P-AlGaAs current spreading layer is a Mg-doped AlGaAs layer with a thickness of 5.035 μm and a Mg doping amount of 3.5×10 18 cm -3 , the hole solubility is 3.5×10 18 cm -3 .

[0133] Comparative Example 3

[0134] This comparative example provides an epitaxial structure of a positive polarity infrared LED, which is basically the same as that of Example 1, except that:

[0135] The epitaxial structure of the positive polarity infrared LED comprises a buffer layer, an N-AlGaAs current spreading layer, an N-AlGaAs confinement layer, a multi-quantum well layer, a P-AlGaAs confinement layer, and a P-type GaAs ohmic contact layer stacked in sequence.

[0136] Performance Testing

[0137] The epitaxial wafers obtained in the embodiment and the comparative example were made into 8*8μm chips for photoelectric performance testing. The specific chip testing method is: when a current of 20mA is passed, the light efficiency improvement rate, luminous intensity and yield of the obtained chip are tested; the light efficiency improvement rate is calculated based on the comparative example 3 which does not contain the P-AlGaAs current spreading layer.

[0138] The test results are shown in Table 1 below.

[0139] Table 1 Test results of LED chips obtained in the examples and comparative examples

[0140] Light efficiency improvement rate (%) Luminous intensity (mW) Yield (%) Example 1 82.9 7.5 96.2 Example 2 78.0 7.3 95.5 Example 3 68.3 6.9 95.7 Example 4 53.7 6.3 85.9 Comparative Example 1 48.8 6.1 87.5 Comparative Example 2 53.7 6.3 84.3 Comparative Example 3 0 4.1 55.5

[0141] From the above results, it can be seen that setting a P-AlGaAs current spreading layer on the P-AlGaAs confinement layer and the P-type GaAs ohmic contact layer, and the P-AlGaAs current spreading layer is a superlattice formed by periodically alternating stacking of C-doped AlGaAs layers and Mg-doped AlGaAs layers, and combining it with a cyclic annealing process, is conducive to distributing the holes in the epitaxial layer more evenly, growing a high-quality and highly uniform epitaxial layer, improving the yield of the LED chip, and at the same time reducing light absorption, effectively improving the luminous efficiency and luminous intensity.

[0142] The above disclosure is only a preferred embodiment of the present invention and certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. An epitaxial structure of a positive polarity infrared LED, characterized in that: It includes a buffer layer, an N-AlGaAs current spreading layer, an N-AlGaAs confinement layer, a multi-quantum well layer, a P-AlGaAs confinement layer, a P-AlGaAs current spreading layer, and a P-type GaAs ohmic contact layer stacked in sequence; The P-AlGaAs current spreading layer is a superlattice formed by periodically alternating stacking of C-doped AlGaAs layers and Mg-doped AlGaAs layers, with the number of periods ranging from 33 to 150. In each period, the C-doped AlGaAs layer is located below the Mg-doped AlGaAs layer. After the Mg-doped AlGaAs layer is grown, it is subjected to annealing treatment, and then the next cycle of C-doped AlGaAs layer is grown. The annealing treatment is: maintaining the temperature at 650° C. to 720° C. for 5 seconds to 10 seconds.

2. The epitaxial structure of the positive polarity infrared LED according to claim 1, wherein: The total thickness of the P-AlGaAs current spreading layer is 4 μm to 9 μm.

3. The epitaxial structure of the positive polarity infrared LED according to claim 1 or 2, characterized in that: The thickness of the C-doped AlGaAs layer is 30 nm to 60 nm, and the thickness of the Mg-doped AlGaAs layer is 30 nm to 60 nm.

4. The epitaxial structure of the positive polarity infrared LED according to claim 1, wherein: The hole concentration in the P-AlGaAs current spreading layer is greater than 3.5×10 18 cm -3 , the doping amount of the C-doped AlGaAs layer is less than the doping amount of the Mg-doped AlGaAs layer.

5. The epitaxial structure of the positive polarity infrared LED according to claim 4, wherein: The C doping amount in the C-doped AlGaAs layer is 3×10 18 cm -3 ~4×10 18 cm -3 ; The doping amount of Mg in the Mg-doped AlGaAs layer is 3.5×10 18 cm -3 ~4.5×10 18 cm -3 .

6. The epitaxial structure of the positive polarity infrared LED according to claim 1, wherein: The Al content in the C-doped AlGaAs layer is 0.1-0.4; The Al content in the Mg-doped AlGaAs layer is 0.1-0.

4.

7. The epitaxial structure of the positive polarity infrared LED according to claim 1, wherein: The growth temperature of the C-doped AlGaAs layer is 650° C. to 720° C., and the growth pressure is 30 to 80 mbar; The growth temperature of the Mg-doped AlGaAs layer is 650° C. to 720° C., and the growth pressure is 30 to 80 mbar.

8. A method for preparing an epitaxial structure of a positive-polarity infrared LED according to any one of claims 1 to 7, characterized in that: include: growing a buffer layer on the substrate; Growing an N-AlGaAs current spreading layer on the buffer layer; growing an N-AlGaAs confinement layer on the N-AlGaAs current spreading layer; Growing a multi-quantum well layer on the N-AlGaAs confinement layer; Growing a P-AlGaAs confinement layer on the multi-quantum well layer; growing a P-AlGaAs current spreading layer on the P-AlGaAs confinement layer; Growing a P-type GaAs ohmic contact layer on the P-AlGaAs current spreading layer; The P-AlGaAs current spreading layer is a superlattice formed by periodically alternating stacking of C-doped AlGaAs layers and Mg-doped AlGaAs layers, wherein in each cycle, the C-doped AlGaAs layer is located below the Mg-doped AlGaAs layer; Growing a P-AlGaAs current spreading layer on a P-AlGaAs confinement layer includes: (1) Control the reaction chamber temperature to maintain at 650℃~720℃, and grow a C-doped AlGaAs layer through C source, Al source, Ga source, and As source; (2) Turn off the C source, introduce Mg source, Al source, Ga source, and As source to grow the Mg-doped AlGaAs layer, completing one cycle of growth; (3) Turn off the group III source and Mg source, maintain the temperature and anneal for 5s~10s; Repeat steps (1) to (3) until the thickness or number of cycles reaches the preset value.

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