A quantum well LED with an AlGaN / InGaN superlattice barrier layer and a preparation method thereof

Abstract

A quantum well LED with an AlGaN / InGaN superlattice barrier layer and a preparation method thereof belong to the technical field of semiconductor light-emitting devices. It is composed of a substrate, a nucleation layer, an n-type GaN layer, a multi-quantum well active layer with an AlGaN / InGaN superlattice barrier layer, an electron blocking layer, and a p-type GaN layer from bottom to top in sequence. An upper electrode and a lower electrode are respectively arranged on the p-type layer and the n-type layer. The electrodes are prepared by thermal evaporation or electron beam evaporation methods, and the remaining layers are prepared by metal organic chemical vapor deposition (MOCVD) methods. After determining the composition of the InGaN well layer in the multi-quantum well according to the required emission wavelength in the present invention, the composition of the superlattice barrier layer is regulated by calculating the polarization intensity and the bandgap width, so that under the condition that the bandgap width of the barrier layer is greater than that of the well layer, the polarization intensity difference between the well layer and the barrier layer can be reduced, thereby reducing the polarization electric field intensity in the quantum well and improving the light-emitting performance of the LED.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor light-emitting devices, and particularly relates to a quantum well LED with an AlGaN / InGaN superlattice barrier layer and a preparation method thereof. Background Art

[0002] Group III nitride semiconductor materials represented by GaN have advantages such as a direct bandgap structure, a wide bandgap coverage range, good thermal stability, and chemical stability. They are now widely used in the preparation of various optoelectronic devices. Among them, light-emitting diodes (LEDs) are the most mature field of application of group III nitride semiconductor materials at present. The active region of GaN-based LEDs mainly adopts a multi-quantum well (MQWs) structure to improve the carrier confinement effect and the light-emitting efficiency of the device. However, the polarization effect of group III nitride materials will cause polarization charges to accumulate at the heterojunction interface, and then generate a polarization electric field on the order of MV / cm. The polarization electric field will bend the energy band of the quantum well, reduce the overlap degree of the electron-hole wave functions in the quantum well, and then greatly reduce the radiative recombination rate of carriers in the quantum well, that is, the quantum-confined Stark effect (QCSE). QCSE results in a low light-emitting efficiency of the LED and a red shift of the emission wavelength.

[0003] In blue LEDs with an InGaN multi-quantum well structure as the well layer, using an AlInGaN quaternary material as the barrier layer of the quantum well structure is one of the methods to reduce the polarization electric field intensity. The AlInGaN quaternary compound can independently regulate the lattice constant and the bandgap width by adjusting the composition. Using AlInGaN with an appropriate composition as the barrier layer of the quantum well can achieve polarization intensity matching with the InGaN well layer, eliminate interface polarization charges, and thus greatly reduce the polarization electric field intensity in the LED quantum well. However, existing research has shown that higher Al and In compositions are required in AlInGaN to achieve polarization intensity matching with InGaN. The high-quality growth of quaternary AlInGaN materials with high Al and In compositions is extremely difficult, and their low crystal quality seriously affects the light-emitting performance of the InGaN / AlInGaN quantum well structure. Summary of the Invention

[0004] The present invention provides a quantum well LED with an AlGaN / InGaN superlattice barrier layer and a preparation method thereof. The quantum well LED of the present invention, by using an AlGaN / InGaN superlattice material as the barrier layer of the quantum well structure and regulating the composition, can greatly reduce the polarization mismatch with the InGaN well layer at lower Al and In compositions compared with AlInGaN, reduce the polarization electric field intensity in the quantum well, improve the light-emitting performance of the LED, and the growth of high-quality AlGaN / InGaN superlattice materials is easier compared with AlInGaN.

[0005] A quantum well LED with an AlGaN / InGaN superlattice barrier layer according to the present invention (see the attached Figure 1 and the accompanying drawings), characterized in that: it is composed of a substrate 1, a nucleation layer 2, an n-type GaN layer 3, a multi-quantum well active layer 4 with an AlGaN / InGaN superlattice barrier layer, an electron blocking layer 5, and a p-type GaN layer 6 from bottom to top in sequence. An upper electrode 7 and a lower electrode 8 are respectively prepared on the p-type GaN layer 6 and the n-type GaN layer 3.

[0006] A quantum well LED with an AlGaN / InGaN superlattice barrier layer as described above, characterized in that: the substrate 1 can be a single crystal substrate such as sapphire, SiC or GaN that can be used for the epitaxial growth of group III nitride materials; the nucleation layer 2 is a low-temperature GaN or AlN layer with a thickness of 20 - 50 nm; the n-type GaN layer 3 is a Si-doped GaN layer with a doping concentration of 10 18 cm -3 order of magnitude and a thickness of 1 - 3 μm; the electron blocking layer 5 is a Mg-doped Al m Ga 1-m N layer, where 0.1 ≤ m ≤ 0.3, with a doping concentration of 10 19 cm -3 order of magnitude and a thickness of 10 - 50 nm; the p-type GaN layer 6 is a Mg-doped GaN layer with a doping concentration of 10 19 cm -3 order of magnitude and a thickness of 100 - 200 nm; the material of the upper electrode 7 can be a single-layer material such as Au, Pt, a binary alloy composite material such as Ni-Au, Ni-Pt, or a ternary alloy composite material such as Ni-Pt-Au, with a thickness of 30 - 120 nm; the material of the lower electrode 8 can be a binary alloy composite material such as Ti-Au, a ternary alloy composite material such as Ti-Al-Au, or a quaternary alloy composite material such as Ti-Al-Ni-Au, Ti-Al-Ti-Au, with a thickness of 60 - 300 nm.

[0007] A quantum well LED with an AlGaN / InGaN superlattice barrier layer as described above, characterized in that: the nucleation layer 2, n-type GaN layer 3, multi-quantum well active layer 4 with an AlGaN / InGaN superlattice barrier layer, electron blocking layer 5, and p-type GaN layer 6 in this LED are all metal-polar or nitrogen-polar materials with a wurtzite crystal structure. The polarity of each layer of material can be regulated by the type of substrate or the substrate surface pretreatment process. For example, epitaxial growth on a sapphire substrate (temperature ≥ 900 °C, treatment time between 10 s and 10 min) after high-temperature nitridation treatment can obtain a nitrogen-polar LED, and epitaxial growth on a sapphire substrate after low-temperature nitridation treatment (temperature ≤ 700 °C, treatment time between 10 s and 10 min) can obtain a metal-polar LED; epitaxial growth on a silicon-face SiC substrate can obtain a metal-polar LED, and epitaxial growth on a carbon-face SiC substrate can obtain a nitrogen-polar LED; epitaxial growth on a gallium-face GaN substrate can obtain a metal-polar LED, and epitaxial growth on a nitrogen-face GaN substrate can obtain a nitrogen-polar LED.

[0008] A quantum well LED with an AlGaN / InGaN superlattice barrier layer as described above, characterized in that: the multi-quantum well active layer 4 has a well layer / barrier layer structure with a logarithm of 1 to 5, and the well layer is In y1 Ga 1-y1 N material, where 0 < y1 < 1, and the thickness of the well layer is 1 to 3 nm; the barrier layer is an Al x Ga 1-x N / In y Ga 1-y N superlattice material, where 0 < x < 1, 0 < y < 1, and in each period of the barrier layer, the thickness of the Al x Ga 1-x N layer is a nm (1 ≤ a ≤ 2), and the thickness of the In y Ga 1-y N layer is b nm (1 ≤ b ≤ 2), and the total thickness of the barrier layer is 10 to 20 nm. In the present invention, first, the composition y1 of the In y1 Ga 1-y1 N well layer in the multi-quantum well active layer 4 is determined according to the desired emission wavelength, and then appropriate Al x Ga 1-x N / In y Ga 1-y N barrier layer components x and y are selected to make the difference in bandgap energy ΔE g > 0 between the barrier layer and the well layer, while reducing the difference in polarization intensity ΔP between the well layer and the barrier layer, and reducing the polarization electric field strength F p .

[0009] Al x Ga1-x N / In y Ga 1-y N superlattice material and In y1 Ga 1-y1 N material. If the specific values of components x, y, and y1 are known, the polarization intensities of both can be calculated through the following theoretical formulas. The specific method is as follows:

[0010] In terms of components, Al x Ga 1-x N / In y Ga 1-y N superlattice material can be equivalent to a quaternary material with the same thickness, where and and respectively satisfy:

[0011]

[0012] Among them, the thickness of the Al x Ga 1-x N layer is a nm, and the thickness of the In y Ga 1-y N layer is b nm.

[0013] After that, calculate the polarization intensity of the quaternary material.

[0014] For the spontaneous polarization intensity, the calculation method is (to make the description more concise, in the following text, the Ga component is replaced by and ):

[0015]

[0016] Among them, P sp (AlN), P sp (InN), and P sp (GaN) are the spontaneous polarization intensities of AlN, InN, and GaN respectively, and their values are -0.09, -0.042, and -0.034 C / m 2 ; b sp,AlInN , b sp,AlGaN and b sp,InGaN are the bending coefficients corresponding to AlInN, AlGaN, and InGaN respectively, and their values are 0.07, 0.021, and 0.037 C / m 2 . The spontaneous polarization intensity of is the spontaneous polarization intensity P of the Al x Ga 1-x N / In y Ga 1-y N superlattice materialsp,SL 。

[0017] For the piezoelectric polarization intensity, the multi-quantum well active layer in this LED is in a state of complete strain with respect to the n-type GaN layer 3. First, find out the strain suffered by the quaternary material grown on the n-type GaN layer 3 The calculation method is as follows:

[0018]

[0019] where a(GaN) is the lattice constant of GaN, and its value is 0.3189 nm; is the lattice constant of The lattice constant of can be obtained from the following formula:

[0020]

[0021] where a(AlN), a(InN), and a(GaN) are the lattice constants of AlN, InN, and GaN respectively, and the values of a(AlN) and a(InN) are 0.3112 and 0.3533 nm respectively.

[0022] However, for the superlattice material, it is necessary to consider the difference in its strain from that of the quaternary material, and then correct Equation ③. For the wurtzite structure semiconductor material constituting the LED in the present invention, the strain energy U accumulated per unit volume is given by the following formula:

[0023]

[0024] where c ij is the elastic coefficient of the material. Taking the material as an example, its calculation method is similar to the form of Equation ④:

[0025]

[0026] where c ij (AB) is the elastic coefficient of this binary material. The calculation method of ε is still obtained from Equation ③.

[0027] In this LED, in each period of the Al x Ga 1-x N / In y Ga 1-y N superlattice, since the AlGaN layer accumulates tensile strain and the InGaN layer accumulates compressive strain, the total strain energy W(SL) of the superlattice in each period is equal to the difference between the two, as shown in the following formula:

[0028]

[0029] And The strain energy of the quaternary material is:

[0030]

[0031] where l is the thickness of each period of the superlattice, and l = a + b. The ratio between the superlattice and the strain energy of the quaternary material is represented by the coefficient B:

[0032]

[0033] After that, we modify Equation ③ with the coefficient B to obtain the strain ε(SL) of the superlattice material:

[0034]

[0035] After that, the piezoelectric polarization intensity of the binary material with ε(SL) as the independent variable is obtained through the following formula:

[0036] P pz (AlN,ε) = -1.808ε + 5.624ε 2 (ε < 0)

[0037] P pz (AlN,ε) = -1.808ε - 7.888ε 2 (ε > 0) ⑩

[0038]

[0039]

[0040] Finally, substitute it into the following formula to obtain the piezoelectric polarization intensity of:

[0041]

[0042] At this time, this piezoelectric polarization intensity is the piezoelectric polarization intensity P x Ga 1-x N / In y Ga 1-y N superlattice. For the piezoelectric polarization intensity of the normal quaternary material, there is no need to consider the correction process of Equations ⑤ - ⑨. Just substitute Equation ③ into Equation pz,SL for calculation.

[0043] The total polarization intensity of the superlattice material is the sum of the spontaneous polarization intensity and the piezoelectric polarization intensity:

[0044]

[0045] When determining In y1 Ga​1-y1 After the In composition y1 of the N-well layer, its polarization electric field strength P tot,well Similarly, it can be obtained by using the method corresponding to the above quaternary material, just substitute into the formula.

[0046] In summary, the polarization intensity difference between the well layer and the barrier layer is:

[0047]

[0048] Furthermore, the polarization electric field strength can be obtained from the following formula:

[0049]

[0050] where L b and L w are the thicknesses of the barrier layer and the well layer in the multiple quantum well respectively, ∈0 is the vacuum permittivity, ∈ b and ∈ w are the relative permittivities of the barrier layer and the well layer respectively. ∈ b and ∈ w can also be obtained by combining the relative permittivities of each binary material in the form of linear interpolation shown in formula ④.

[0051] For the Al x Ga 1-x N / In y Ga 1-y N superlattice barrier layer, its bandgap can be obtained by the following formula:

[0052]

[0053] where E g (AlN), E g (InN) and E g (GaN) are the bandgaps of AlN, InN and GaN respectively, and their values are 6.16, 0.76 and 3.44 eV; b Eg (AlInN), b Eg (AlGaN) and b Eg (InGaN) are the corresponding bending coefficients of AlInN, AlGaN and InGaN respectively, and their values are 3.477, 0.688 and 1.416 eV. The bandgap of can be regarded as the bandgap E x Ga 1- x N / In y Ga 1-y N superlattice. For the well layer In g,SL . y1 Ga1-y1 The N bandgap E g,well can be obtained from the required emission wavelength λ by the method described below.

[0054] Next, find the difference in the bandgaps between the barrier layer and the well layer:

[0055]

[0056] When changing the compositions x and y, it is necessary to ensure that ΔE g > 0.

[0057] The multi-quantum well active layer 4 as described above is characterized in that: the In composition y1 of the well layer is determined according to the required emission wavelength λ (unit: μm). First, from E g = 1.24 / λ, find the required bandgap E y1 Ga 1-y1 N of the well layer, and then substitute E g,well (unit: eV) into Equation g,well (at this time in Equation ) to solve for the In composition y1. in )

[0058] In summary, when we know the compositions x and y of the Al x Ga 1-x N / In y Ga 1-y N superlattice barrier layer and the composition y1 of the In y1 Ga 1-y1 N well layer, we can find the difference in polarization intensity ΔP between the well layer and the barrier layer and the polarization electric field strength F in the quantum well through Equation p . Since the composition y1 of the In y1 Ga 1-y1 N well layer needs to be determined according to the required emission wavelength, y1 can be regarded as a fixed value. We can reduce the value of |ΔP| by changing the compositions x and y of the barrier layer, thereby reducing the polarization electric field strength F p . Generally, increasing the In composition y in the Al x Ga 1-x N / In y Ga 1-y N superlattice barrier layer is beneficial to reducing |ΔP|, but too high In composition will degrade the crystal quality of the superlattice material and reduce the bandgap of the barrier layer, thereby reducing the confinement effect of the quantum well on carriers. Increasing the Al composition x can increase the bandgap of the barrier layer, but it will also increase |ΔP|. Therefore, the values of x and y need to satisfy: the difference in bandgaps ΔE between the barrier layer and the well layer gwhile >0, reducing the polarization intensity difference ΔP between the well layer and the barrier layer, and reducing the polarization electric field strength F in the quantum well p 。

[0059] A quantum well LED with an AlGaN / InGaN superlattice barrier layer as described above, and its manufacturing method is as follows:

[0060] Using metal organic chemical vapor deposition (MOCVD) method, successively epitaxially grow a nucleation layer 2, an n-type GaN layer 3, a multi-quantum well active layer 4 with an AlGaN / InGaN superlattice barrier layer, an electron blocking layer 5, and a p-type GaN layer 6 on a substrate 1; use nitrogen as the carrier gas when growing the multi-quantum well active layer 4, and use hydrogen as the carrier gas when growing the rest; use trimethylaluminum (TMAl), trimethylindium (TMIn), and trimethylgallium (TMGa) as the Al source, In source, and Ga source respectively, use high-purity ammonia gas as the N source, use silane as the n-type doping source, and use bis(cyclopentadienyl)magnesium as the p-type doping source; the growth temperature of the nucleation layer 2 is 530 - 550 °C, the growth pressure is 100 - 400 mbar, and the growth thickness is 20 - 50 nm; the growth temperature of the n-type GaN layer 3 is 1000 - 1100 °C, the growth pressure is 100 - 400 mbar, the growth thickness is 1 - 3 μm, and the n-type doping concentration is 10 18 cm -3 magnitude; in the multi-quantum well active layer 4, the growth temperature of the InGaN well layer is 700 - 800 °C, the growth pressure is 100 - 400 mbar, and the growth thickness is 1 - 3 nm; the AlGaN / InGaN superlattice barrier layer is grown by the pulse method. During one pulse cycle, ammonia gas is continuously introduced. First, TMAl and TMGa are successively introduced to grow the AlGaN layer, and then TMIn and TMGa are successively introduced to grow the InGaN layer. According to this time sequence mode, cycle 5 - 10 times. The growth temperature is 700 - 850 °C, the growth pressure is 100 - 400 mbar, the thicknesses of both the AlGaN layer and the InGaN layer are 1 - 2 nm, the total thickness of the superlattice barrier layer is 10 - 20 nm, and the number of pairs of quantum wells is 1 - 5; when growing the multi-quantum well active layer 4, various growth parameters need to be continuously adjusted to make the compositions of the well layer and the barrier layer reach the theoretical expected values to achieve a quantum well structure with a weak polarization electric field strength. For example, increasing or decreasing the Al component can be achieved by increasing or decreasing the TMAl flow rate, and increasing or decreasing the In component can be achieved by decreasing or increasing the growth temperature; the growth temperature of the electron blocking layer 5 is 900 - 1000 °C, the growth pressure is 100 - 400 mbar, the growth thickness is 10 - 50 nm, and the p-type doping concentration is 10 19 cm -3Magnitude; the growth temperature of the p-type GaN layer 6 is 900 - 1000 °C, the growth pressure is 100 - 400 mbar, the growth thickness is 100 - 200 nm, and the p-type doping concentration is 10 19 cm -3 magnitude.

[0061] Etch the area on one side of the upper surface of the p-type GaN layer 6 to the n-type GaN layer 3 by methods such as inductively coupled plasma (ICP) etching to obtain an exposed n-type GaN layer 3 mesa; then prepare the upper electrode 7 and the lower electrode 8 on the p-type layer 6 and the exposed n-type GaN layer 3 mesa respectively by thermal evaporation or electron beam evaporation methods. The material of the upper electrode 7 can be monolayer materials such as Au, Pt, binary alloy composite materials such as Ni - Au, Ni - Pt, or ternary alloy composite materials such as Ni - Pt - Au, with a thickness of 30 - 120 nm; the material of the lower electrode 8 can be binary alloy composite materials such as Ti - Au, ternary alloy composite materials such as Ti - Al - Au, or quaternary alloy composite materials such as Ti - Al - Ni - Au, Ti - Al - Ti - Au, with a thickness of 60 - 300 nm.

[0062] The effects and benefits of the present invention: (1) Using the AlGaN / InGaN superlattice material as the barrier layer of the LED multi-quantum well, the polarization mismatch between the well layer and the barrier layer can be reduced by adjusting the composition, greatly reducing the polarization electric field intensity in the quantum well, which is beneficial to improving the light-emitting performance of the LED. (2) Compared with the AlInGaN barrier layer, the AlGaN / InGaN superlattice material can form a weak polarization electric field quantum well structure with the well layer at lower Al and In compositions, which is beneficial to improving the crystal quality of the barrier layer material and further improving the light-emitting performance of the LED. Description of the Drawings

[0063] Figure 1 : Schematic diagram of the structure of the quantum well LED with an AlGaN / InGaN superlattice barrier layer of the present invention. In the figure, 1 is the substrate, 2 is the nucleation layer, 3 is the n-type GaN layer, 4 is the multi-quantum well active layer with an AlGaN / InGaN superlattice barrier layer, 5 is the electron blocking layer, 6 is the p-type GaN layer, 7 is the upper electrode, and 8 is the lower electrode.

[0064] Figure 2 : Sample 1 (In 0.15 Ga 0.85 N / GaN quantum well structure) and Sample 2 (In 0.15 Ga 0.85 N / superlattice material quantum well structure) variable power photoluminescence (PL) test results (the blue shift amount of the emission peak position with the increase of the excitation power is marked in the figure).

[0065] Figure 3: LED sample 3 (using In 0.15 Ga 0.85 N / GaN quantum well structure) and sample 4 (using In 0.15 Ga 0.85 N / superlattice material quantum well structure), the curve of the normalized power conversion efficiency varying with the current density (where the difference between the peak efficiency and the efficiency corresponding to the maximum current density, i.e., the value of the Droop effect, has been marked in the figure). Detailed implementation manners

[0066] Example 1:

[0067] The InGaN / GaN quantum well structure and the InGaN / superlattice quantum well structure are epitaxially grown by MOCVD, named sample 1 and sample 2 respectively. The specific structures of the two samples include Figure 1 substrate 1, GaN nucleation layer 2, n-type GaN layer 3 and multi-quantum well active layer 4. The multi-quantum well active layer 4 of sample 1 is an InGaN / GaN multi-quantum well structure, while the multi-quantum well active layer 4 of sample 2 is an InGaN / superlattice material multi-quantum well structure. The structures and parameters of the remaining parts are exactly the same, and the specific information of each layer will be introduced in detail in the following growth steps.

[0068] The specific steps for growing sample 2 are as follows: Using MOCVD equipment, first perform low-temperature nitridation treatment on the double-polished sapphire substrate 1 at a temperature of 540 °C for 180 s. Then, successively epitaxially grow the GaN nucleation layer 2, n-type GaN layer 3 and the multi-quantum well active layer 4 with an InGaN / superlattice material multi-quantum well structure on the substrate. Nitrogen is used as the carrier gas when growing the multi-quantum well active layer 4, and hydrogen is used as the carrier gas when growing the remaining parts. The group III sources are TMAl, TMIn and TMGa, the group V source is high-purity ammonia, the n-type doping source is silane, and the p-type doping source is bis(cyclopentadienyl)magnesium. The growth temperature of the nucleation layer 2 is 540 °C, the growth pressure is 200 mbar, and the thickness is 40 nm. The growth temperature of the n-type GaN layer 3 is 1050 °C, the growth pressure is 200 mbar, the thickness is 3 μm, and the n-type doping concentration is 5×10 18 cm -3In the multi-quantum well active layer 4, the growth temperature of the InGaN well layer is 750 °C, the growth pressure is 400 mbar, the flow rates of TMIn, TMGa, and ammonia are 6.8 μmol / min, 2.9 μmol / min, and 233 mmol / min respectively, the thickness is 2.5 nm, and the In composition y1 is 0.15; the AlGaN / InGaN superlattice barrier layer is grown by the pulse method. During one pulse cycle, ammonia is continuously introduced. First, TMAl and TMGa are introduced in sequence to grow the AlGaN layer, and then TMIn and TMGa are introduced in sequence to grow the InGaN layer. This time sequence pattern is cycled 6 times. The growth temperature is 720 °C, the growth pressure is 400 mbar. When growing the AlGaN layer, the flow rates of TMAl, TMGa, and ammonia are 2.14 μmol / min, 17.3 μmol / min, and 44.6 mmol / min respectively. When growing the InGaN layer, the flow rates of TMIn, TMGa, and ammonia are 6.8 μmol / min, 2.9 μmol / min, and 233 mmol / min respectively. The thicknesses of both the AlGaN layer and the InGaN layer are 1.1 nm. The Al composition x in the AlGaN layer is 0.1, and the In composition y in the InGaN layer is 0.13. The number of quantum wells is 2. In the epitaxial growth of Sample 1, the barrier layer of the quantum well is GaN, and the continuous growth mode is adopted. The growth temperature is 720 °C, the growth pressure is 400 mbar, the thickness is 13.2 nm, and the remaining steps and parameters are the same as those of Sample 2.

[0069] The following describes the relevant calculation processes of the two samples in combination with the calculation methods of polarization intensity and bandgap width in the above text:

[0070] The emission wavelength we need is 0.434 μm in the blue light band. By using E g = 1.24 / λ, the bandgap widths E y1 Ga 1-y1 N well layers corresponding to the two samples are obtained as E g,well = 2.86 eV. Then, through Equation the In composition y1 = 0.15 is solved. Through Equation ②, the spontaneous polarization intensity P sp,well = -0.030 C / m 2 of the well layer is obtained; for the piezoelectric polarization intensity, first, the strain ε well = -0.016 is obtained through Equations ③ and ④, and then the piezoelectric polarization intensity P is obtained through Equation pz,well = 0.019 C / m 2 . Finally, through Equation the total polarization intensity P tot,well = -0.011 C / m 2 of the well layer is obtained.

[0071] For the barrier layer GaN of sample 1, the spontaneous polarization intensity P sp,GaN =-0.034C / m 2 ; For the piezoelectric polarization strength, first calculate the strain ε through equations ③ and ④ GaN = 0, then through the formula Calculate the piezoelectric polarization intensity P pz,GaN = 0. By formula Calculate the total polarization strength P of the GaN barrier layer tot,GaN =-0.034C / m 2 . Pass-through The difference in polarization intensity between the well layer and the barrier layer of sample 1 is ΔP1 = 0.023 C / m 2 , the final passing formula Calculate the polarization electric field strength F in the quantum well of sample 1 p1 =2.12MV / cm. The bandgap of GaN is 3.44eV. Calculate the difference in bandgap width between the barrier layer and the well layer, ΔE g1 =0.58eV, satisfying ΔE g1 >0.

[0072] For the barrier layer of sample 2, Al 0.1 Ga 0.9 N / In 0.13 Ga 0.87 N superlattice material, first calculate its equivalent components through formula ① The spontaneous polarization intensity P is obtained by formula ② sp,SL =-0.034C / m 2 For the piezoelectric polarization strength, first use equations ③ and ④ to calculate the strain ε before correction SL =-0.006, and then use equations ⑤ to ⑧ to obtain the correction coefficient B = 2.63, and use equation ⑨ to obtain the corrected strain ε B,SL =-0.016, and finally through the formula Calculate the piezoelectric polarization intensity P pz,SL =0.018C / m 2 . Pass-through Calculate the total polarization intensity P of the superlattice barrier layer tot,SL =-0.016C / m 2 . Pass-through The difference in polarization intensity between the well layer and the barrier layer of sample 2 is ΔP2 = 0.005 C / m 2 , the final passing formula Calculate the polarization electric field strength F in the quantum well of sample 2 p2 =0.50MV / cm. Calculate the bandgap width E of the barrier layer g,SL =3.28eV, through the formula Calculate the difference in bandgap energy ΔE between the barrier layer and the well layer g2 = 0.42 eV, satisfying ΔE g2 > 0.

[0073] From the above calculation results, it can be seen that under the condition that the bandgap energy of the barrier layer of Sample 2 is greater than that of the well layer, the polarization electric field intensity of the quantum well structure of Sample 2 decreases significantly compared with that of Sample 1 with the traditional quantum well structure, reflecting the important role of the Al 0.1 Ga 0.9 N / In 0.13 Ga 0.87 N superlattice barrier layer in reducing the polarization electric field intensity.

[0074] Figure 2 are the variable-power PL test results of Sample 1 and Sample 2. It can be seen from the figure that as the excitation power increases, the blue shift amount of the emission peak position of Sample 2 is significantly lower than that of Sample 1, indicating that the polarization electric field intensity in the quantum well of Sample 2 with the AlGaN / InGaN superlattice as the barrier layer is significantly lower than that of Sample 1. Because the blue shift of the emission peak position with the increase of the excitation power is due to the increase of the carriers injected into the active region, the screening effect of the carriers on the polarization charges is enhanced, resulting in the weakening of the polarization electric field and the quantum-confined Stark effect; therefore, the smaller the blue shift amount, the lower the original polarization electric field intensity in the sample.

[0075] Example 2:

[0076] Based on the quantum well structures of Sample 1 and Sample 2 in Example 1, the complete LEDs shown are further prepared Figure 1 and named Sample 3 and Sample 4 respectively. The specific structures of the two samples include Figure 1 the substrate 1, the nucleation layer 2, the n-type GaN layer 3, the multi-quantum well active layer 4, the electron blocking layer 5 and the p-type GaN layer 6 in , and an upper electrode 7 and a lower electrode 8 are respectively prepared on the p-type GaN layer 6 and the n-type GaN layer 3. The multi-quantum well active layer 4 of Sample 1 is an InGaN / GaN multi-quantum well structure, while the multi-quantum well active layer 4 of Sample 2 is an InGaN / superlattice material multi-quantum well structure, and the structures and parameters of the rest are exactly the same. The specific information of each layer will be introduced in the growth steps. Taking Sample 3 as an example, the subsequent preparation steps based on Example 1 are: continue to epitaxially grow the Al 0.3 Ga 0.7 N electron blocking layer 5 and the p-type GaN layer 6 on the basis of the structure of Sample 1 by MOCVD. Al 0.3 Ga 0.7The growth temperature of the N electron blocking layer 5 is 940 °C, the growth pressure is 200 mbar, the flow rates of TMAl, TMGa and ammonia are 13.5 μmol / L, 31.4 μmol / L and 233 mmol / min respectively, the thickness is 20 nm, and the p-type doping concentration is 5×10 19 cm -3 . The growth temperature of the p-type GaN layer 6 is 940 °C, the growth pressure is 200 mbar, the thickness is 150 nm, and the p-type doping concentration is 5×10 19 cm -3 . The area on one side of the upper surface of the p-type GaN layer 6 is etched to the n-type GaN layer 3 by inductively coupled plasma (ICP) etching method (using boron chloride and chlorine with a gas flow ratio of 1:9 and a plate power of 100 W) to obtain an exposed mesa of the n-type GaN layer 3. The upper electrode 7 made of Ni-Au binary alloy (with a thickness of 60 nm, a Ni layer thickness of 30 nm, an Au layer thickness of 30 nm, evaporation sources being Ni metal and Au metal, and evaporation rates being 3.6 nm / min and 2.4 nm / min respectively) is prepared on the unetched p-type GaN layer 6 by thermal evaporation method; the lower electrode 8 made of Ti / Al / Ti / Au (with a thickness of 260 nm, each layer thickness being 40 nm, 150 nm, 20 nm, 50 nm respectively, evaporation sources being Ti metal, Al metal and Au metal, and evaporation rates being 3.6 nm / min, 4.8 nm / min and 2.4 nm / min respectively) is prepared on the exposed mesa of the n-type GaN layer 3 by thermal evaporation method, thus obtaining a complete LED. The subsequent preparation steps of Sample 4 are the same as those of Sample 3.

[0077] Figure 3 shows the relationship between the normalized power conversion efficiency and the current density of Sample 3 and Sample 4. The values of the Droop effect are marked in the figure. It can be seen from the figure that the Droop effect value of Sample 4 is significantly lower than that of Sample 3, reflecting the advantage of the quantum well LED with an AlGaN / InGaN superlattice barrier layer in terms of luminescence performance compared with the traditional InGaN / GaN quantum well LED.

Claims

1. A quantum well LED with an AlGaN / InGaN superlattice barrier layer, which is composed of a substrate (1), a nucleation layer (2), an n-type GaN layer (3), a multi-quantum well active layer (4) with an AlGaN / InGaN superlattice barrier layer, an electron blocking layer (5), and a p-type GaN layer (6) from bottom to top. An upper electrode (7) and a lower electrode (8) are respectively prepared on the p-type GaN layer (6) and the n-type GaN layer (3); the multi-quantum well active layer 4 has a well layer / barrier layer structure with a logarithm of 1 to 5, and the well layer is In y1 Ga 1-y1 N material, where 0 < y1 < 1; the barrier layer is an Al x Ga 1-x N / In y Ga 1-y N superlattice material, where 0 < x < 1, 0 < y < 1; the values of x and y make the difference in the bandgap widths Δ between the barrier layer and the well layer, while reducing the difference in the polarization intensities Δ between the well layer and the barrier layer, and reducing the polarization electric field intensity in the quantum well ; It is characterized in that: The LED is a device structure based on nitrogen-polar group-III nitride materials. A nitrogen-polar LED device structure can be obtained by epitaxial growth on a sapphire substrate subjected to high-temperature nitridation treatment, a carbon-face SiC substrate, and a nitrogen-face GaN substrate.

2. A quantum well LED with an AlGaN / InGaN superlattice barrier layer according to claim 1, characterized in that: The substrate (1) is sapphire, SiC or GaN; the nucleation layer (2) is a low-temperature GaN or AlN layer with a thickness of 20 - 50 nm; the n-type GaN layer (3) is an Si-doped GaN layer with a doping concentration of 10 18 cm -3 order of magnitude and a thickness of 1 - 3 μm; the electron blocking layer (5) is an Mg-doped Al m Ga 1- m N layer, where 0.1 ≤ m ≤ 0.3, with a doping concentration of 10 19 cm -3 order of magnitude and a thickness of 10 - 50 nm; the p-type GaN layer (6) is an Mg-doped GaN layer with a doping concentration of 10 19 cm -3 order of magnitude and a thickness of 100 - 200 nm; the upper electrode (7) is Au, Pt, Ni - Au, Ni - Pt or Ni - Pt - Au with a thickness of 30 - 120 nm; the lower electrode (8) is Ti - Au, Ti - Al - Au, Ti - Al - Ni - Au or Ti - Al - Ti - Au with a thickness of 60 - 300 nm; the well layer has a thickness of 1 - 3 nm; in each period of the barrier layer, the thickness of the Al x Ga 1-x N layer is a nm, 1 ≤ a ≤ 2, and the thickness of the In y Ga 1-y N layer is b nm, 1 ≤ b ≤ 2, and the total thickness of the barrier layer is 10 - 20 nm.

3. A preparation method for a quantum well LED with an AlGaN / InGaN superlattice barrier layer according to any one of claims 1 to 2, the steps are as follows: (1) Use metalorganic chemical vapor deposition method to epitaxially grow a nucleation layer (2), an n-type GaN layer (3), a multi-quantum well active layer (4) with an AlGaN / InGaN superlattice barrier layer, an electron blocking layer (5), and a p-type GaN layer (6) on the substrate (1) in sequence; use nitrogen as the carrier gas when growing the multi-quantum well active layer (4), and use hydrogen as the carrier gas when growing the rest; use TMAl, TMIn, and TMGa as the Al source, In source, and Ga source respectively, use high-purity ammonia as the N source, use silane as the n-type doping source, and use bis(cyclopentadienyl)magnesium as the p-type doping source; the growth temperature of the nucleation layer (2) is 530 - 550 °C, and the growth pressure is 100 - 400 mbar; the growth temperature of the n-type GaN layer (3) is 1000 - 1100 °C, the growth pressure is 100 - 400 mbar, and the n-type doping concentration is 10 18 cm -3Magnitude; in the multi-quantum well active layer (4), the growth temperature of the InGaN well layer is 700 - 800 °C, and the growth pressure is 100 - 400 mbar; the AlGaN / InGaN superlattice barrier layer is grown by the pulse method. During one pulse period, ammonia gas is continuously introduced. First, TMAl and TMGa are sequentially introduced to grow the AlGaN layer, and then TMIn and TMGa are sequentially introduced to grow the InGaN layer. The growth temperature is 700 - 850 °C, and the growth pressure is 100 - 400 mbar; the growth temperature of the electron blocking layer (5) is 900 - 1000 °C, the growth pressure is 100 - 400 mbar, and the p-type doping concentration is 10 19 cm -3 Magnitude; the growth temperature of the p-type GaN layer (6) is 900 - 1000 °C, the growth pressure is 100 - 400 mbar, and the p-type doping concentration is 10 19 cm -3 Magnitude; (2) Etch the area on one side of the upper surface of the p-type GaN layer (6) to the n-type GaN layer (3) by methods such as inductively coupled plasma etching to obtain an exposed n-type GaN layer (3) mesa; then, an upper electrode (7) and a lower electrode (8) are respectively prepared on the p-type layer (6) and the exposed n-type GaN layer (3) mesa by thermal evaporation or electron beam evaporation methods, thereby preparing a quantum well LED with an AlGaN / InGaN superlattice barrier layer.

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