Epitaxial structure based on AlInN hole injection tunnel junction layer and deep ultraviolet photoelectric device

Abstract

The invention relates to the field of semiconductors, and discloses an epitaxial structure and a deep ultraviolet photoelectric device based on an AlInN hole injection tunnel junction layer, and the epitaxial structure comprises a substrate, and a buffer layer, a superlattice layer, an n-type semiconductor layer, a multi-quantum well layer and a tunnel junction layer which are located on the upper surface of the substrate and are sequentially stacked in the direction away from the substrate, the tunnel junction layer comprises a heavily doped p-type AlInN hole injection layer, an intrinsic polarization AlGaN layer and a heavily doped n-type AlInN layer. The layer material of the hole injection layer is AlInN, under the same forbidden bandwidth, the AlInN material has larger lattice constant, intrinsic polarization and piezoelectric polarization than the AlGaN material, polarization surface charges with higher density can be generated at the interface of the AlInN material and the intrinsic polarization AlGaN layer, the electric field intensity of a tunnel junction space charge region is increased, the energy band bending of the tunnel junction space charge region is enhanced, and the hole injection efficiency is improved. Carrier tunneling is promoted, and the electrical performance and the wall insertion efficiency of the epitaxial structure are improved.

Description

Technical Field

[0001] This application relates to the semiconductor field, and in particular to an epitaxial structure and a deep ultraviolet optoelectronic device based on an AlInN hole injection tunnel junction. Background Technology

[0002] Epitaxial structures are an important part of deep ultraviolet optoelectronic devices. AlGaN material is commonly used in epitaxial structures, but AlGaN-based deep ultraviolet optoelectronic devices face significant technical challenges in practical applications.

[0003] The low doping efficiency of p-type AlGaN is a key issue contributing to the significant decrease in internal quantum efficiency (IQE) of the device. Magnesium (Mg) is typically used as the acceptor impurity for p-type doping, but Mg has low solubility and high activation energy in high-Al composition AlGaN, resulting in low hole concentration and high resistance in the p-type layer, leading to insufficient hole injection efficiency and limiting the device's electrical performance. Furthermore, when AlGaN is used as the p-type contact layer, the large work function of p-type AlGaN makes it difficult to find a metal to form an ohmic contact, thus creating a Schottky barrier and increasing the device resistance.

[0004] To address this issue, tunnel junction technology has been introduced into the design of AlGaN-based deep ultraviolet optoelectronic devices. Tunnel junctions achieve interband tunneling through heavily doped pn junctions, effectively reducing device resistance and improving carrier injection efficiency. However, current tunnel junction technology still has shortcomings. First, the doping of Mg into the p-type AlGaN hole injection layer leads to severe local lattice mismatch around Mg. Therefore, the high temperatures during AlGaN growth cause Mg atoms to diffuse to varying degrees into both the upper and lower layers, with upward diffusion being dominant. Simultaneously, interrupting the Mg precursor source (magnesium pyrocene) supply during epitaxial growth causes residual Mg atoms in the reaction chamber walls to be blown onto the epitaxial surface, forming unintentional doping—the Mg memory effect. These Mg atoms on the p-type AlGaN surface diffuse into the subsequently grown intrinsic polarization layer and n-type AlGaN layer, forming a co-doped n-type layer. Carrier compensation impairs the electrical performance of the epitaxial structure and reduces wall insertion efficiency. In other words, the p-type AlGaN hole injection layer suffers from severe Mg precipitation and memory effect, resulting in poor electrical performance of the epitaxial structure. Secondly, due to the significant Mg precipitation during high-temperature growth, the Mg concentration in the p-type AlGaN hole injection layer is relatively low, leading to a low carrier concentration. The concentration requirement can only be met by increasing the thickness of the p-type AlGaN hole injection layer; however, a thicker layer results in a higher overall resistivity of the epitaxial structure. Therefore, the doping concentration and thickness control of the p-type AlGaN hole injection layer have not yet reached optimal levels, affecting tunneling efficiency and device performance.

[0005] Therefore, how to solve the above-mentioned technical problems should be a key focus for those skilled in the art. Summary of the Invention

[0006] The purpose of this application is to provide an epitaxial structure and a deep ultraviolet optoelectronic device based on an AlInN hole injection tunnel junction, so as to improve the electrical performance and wall insertion efficiency of the epitaxial structure.

[0007] To address the aforementioned technical problems, this application provides an epitaxial structure based on an AlInN hole injection tunneling layer, comprising:

[0008] A substrate, wherein a buffer layer, a superlattice layer, an n-type semiconductor layer, a multiple quantum well layer and a tunnel junction layer are sequentially stacked on the upper surface of the substrate in a direction away from the substrate, the tunnel junction layer comprising a heavily doped p-type AlInN hole injection layer, an intrinsically polarized AlGaN layer and a heavily doped n-type AlInN layer.

[0009] Optionally, it also includes:

[0010] An electron blocking layer located between the multi-quantum well layer and the tunnel junction layer.

[0011] Optionally, the doping concentration in the p-type AlInN hole injection layer ranges from 5 × 10⁻⁶. 19 ~1×10 20 cm -3 .

[0012] Optionally, the InN composition in the p-type AlInN hole injection layer ranges from 0.1 to 0.2.

[0013] Optionally, the doping concentration in the n-type AlInN layer ranges from 5 × 10⁻⁶. 19 ~1×10 20 cm -3 .

[0014] Optionally, the InN composition in the n-type AlInN layer ranges from 0.1 to 0.2.

[0015] Optionally, the thickness of the p-type AlInN hole injection layer ranges from 10 nm to 50 nm; and / or, the thickness of the n-type AlInN layer ranges from 10 nm to 100 nm; and / or, the thickness of the intrinsically polarized AlGaN layer ranges from 6 nm to 12 nm.

[0016] Optionally, the lattice constants of the intrinsically polarized AlGaN layers are all greater than the lattice constants of the p-type AlInN hole injection layer and the n-type AlInN layer.

[0017] Optionally, the lattice constants of the intrinsically polarized AlGaN layers are all smaller than the lattice constants of the p-type AlInN hole injection layer and the n-type AlInN layer.

[0018] This application also provides a deep ultraviolet optoelectronic device, including the epitaxial structure based on the AlInN hole injection tunneling layer described above.

[0019] The epitaxial structure based on an AlInN hole injection tunnel junction layer provided in this application includes: a substrate, and a buffer layer, a superlattice layer, an n-type semiconductor layer, a multiple quantum well layer and a tunnel junction layer sequentially stacked on the upper surface of the substrate away from the substrate. The tunnel junction layer includes a heavily doped p-type AlInN hole injection layer, an intrinsically polarized AlGaN layer and a heavily doped n-type AlInN layer.

[0020] As can be seen, the epitaxial structure in this application employs tunnel junction technology. The tunnel junction layer includes a heavily doped p-type AlInN hole injection layer, an intrinsically polarized AlGaN layer, and a heavily doped n-type AlInN layer. Specifically, the hole injection layer in the epitaxial structure of this application is made of AlInN. Under the same bandgap width, AlInN has a larger lattice constant, intrinsic polarization, and piezoelectric polarization than AlGaN. Therefore, the heavily doped AlInN hole injection layer can generate a higher density of polarized surface charge at the interface with the intrinsically polarized AlGaN layer compared to the heavily doped AlGaN hole injection layer. This increases the electric field strength in the space charge region of the tunnel junction, strengthens the band bending in the space charge region, promotes carrier tunneling, and improves the electrical performance and wall insertion efficiency of the epitaxial structure. Furthermore, during high-temperature growth, because In atoms have a high vapor pressure at high temperatures, they easily volatilize from the growth surface, resulting in lower solubility of In atoms in the crystal lattice compared to Mg atoms. This makes it easier for Mg atoms to remain in the crystal, effectively suppressing Mg precipitation and increasing the Mg doping concentration. Because the doping concentration in the p-type AlInN hole injection layer is increased, the thickness of the p-type AlInN hole injection layer can be reduced in this application, thereby reducing the overall resistance of the epitaxial structure.

[0021] In addition, this application also provides a deep ultraviolet optoelectronic device with the above-mentioned advantages. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1A schematic diagram of an epitaxial structure based on an AlInN hole injection tunneling layer provided in this application embodiment. Figure 1 ;

[0024] Figure 2 This is a schematic diagram of the structure of a wurtzite supercell model;

[0025] Figure 3 A comparison diagram of the enthalpy of Mg impurity formation in AlGaN / AlInN with different GaN / InN compositions;

[0026] Figure 4 A schematic diagram of an epitaxial structure based on an AlInN hole injection tunneling layer provided in this application embodiment. Figure 2 ;

[0027] Figure 5 A schematic diagram of the polarization surface charge types generated when the intrinsically polarized AlGaN layer in the tunnel structure is a compressive stress insertion layer;

[0028] Figure 6 A schematic diagram of the polarization surface charge types generated when the intrinsically polarized AlGaN layer in the tunnel structure is a tensile stress insertion layer;

[0029] Figure 7 The current-voltage characteristic curve of the simulated deep ultraviolet LED chip;

[0030] Figure 8 The simulated deep ultraviolet LED chip light output power characteristic curve;

[0031] Figure 9 The simulated deep ultraviolet LED chip wall socket efficiency characteristic curve;

[0032] Figure 10 The graph shows the quantum well radiative recombination rate of a simulated deep ultraviolet LED chip under a current of 300 mA.

[0033] Figure 11 The graph shows the quantum efficiency characteristics of a simulated deep ultraviolet LED chip.

[0034] In the figure, 1 is the substrate, 2 is the buffer layer, 3 is the superlattice layer, 4 is the n-type semiconductor layer, 5 is the multiple quantum well layer, 6 is the p-type AlInN hole injection layer, 7 is the intrinsically polarized AlGaN layer, 8 is the heavily doped n-type AlInN layer, and 9 is the electron blocking layer. Detailed Implementation

[0035] To enable those skilled in the art to better understand the present application, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some embodiments of the present application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0036] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0037] As described in the background section, current epitaxial structures using tunnel junction technology employ heavily doped p-type AlGaN hole injection layers, which suffer from severe Mg precipitation and memory effect, resulting in poor electrical performance of the epitaxial structures. Furthermore, the doping concentration and thickness of the p-type AlGaN hole injection layer have not yet been optimally controlled, affecting tunneling efficiency and device performance.

[0038] In view of this, this application provides an epitaxial structure based on an AlInN hole injection tunneling layer, please refer to... Figure 1 ,include:

[0039] Substrate 1, and a buffer layer 2, a superlattice layer 3, an n-type semiconductor layer 4, a multiple quantum well layer 5 and a tunnel junction layer are sequentially stacked on the upper surface of the substrate 1 in a direction away from the substrate 1. The tunnel junction layer includes a heavily doped p-type AlInN hole injection layer 6, an intrinsically polarized AlGaN layer 7 and a heavily doped n-type AlInN layer 8.

[0040] The material of buffer layer 2 can be AlN. Buffer layer 2 serves as a transition layer between substrate 1 and superlattice layer 3, which can effectively alleviate the stress caused by lattice mismatch and improve the crystal quality.

[0041] This application does not limit the substrate 1 and it can be set by itself. For example, substrate 1 includes, but is not limited to, any one of c-plane sapphire substrate, Si substrate, and SiC substrate.

[0042] The superlattice layer 3 can be a periodic AlN film / GaN film, with one AlN film and one GaN film forming one period. The number of periods of the superlattice layer 3 can be 10 to 40. The thickness of the AlN film ranges from 5 nm to 15 nm, and the thickness of the GaN film ranges from 5 nm to 20 nm.

[0043] The n-type semiconductor layer 4 can be a Si-doped n-type AlGaN layer, with a Si doping concentration of 1×10⁻⁶. 19~5×10 19 cm -3 In an n-type AlGaN layer, the Ga content can be 0.5, meaning the n-type AlGaN layer is an n-type Al 0.5 Ga 0.5 N-layer. The thickness of the n-type semiconductor layer 4 can be 2 μm.

[0044] The multi-quantum-well layer 5 includes 3 periods of Al x Ga 1-x N film / Al y Ga 1-y N film, one layer of Al x Ga 1-x N film and a layer of Al y Ga 1-y The N-layer is one period, where x ranges from 0.35 to 0.45, y ranges from 0.45 to 0.55, and x < y. In each period of the multi-quantum-well layer 5, Al... x Ga 1-x The thickness of N can be 2 nm, and Al y Ga 1-y The thickness of N can be 10 nm.

[0045] The heavily doped p-type AlInN hole injection layer 6 uses Mg atoms as the dopant, with a doping concentration of 1×10⁶. 19 cm -3 The above is referred to as heavy doping.

[0046] It should be noted that this application does not limit the specific doping concentration of the heavily doped p-type AlInN hole injection layer 6, and the doping concentration is within 1×10⁻⁶. 19 cm -3 That's all.

[0047] As one possible implementation, the doping concentration in the p-type AlInN hole injection layer 6 can be in the range of 5 × 10⁻⁶. 19 ~1×10 20 cm -3 .

[0048] It should also be noted that this application does not limit the composition of InN in the p-type AlInN hole injection layer 6, and it can be set by the user.

[0049] In one embodiment of this application, the InN composition range in the p-type AlInN hole injection layer 6 can be 0.1~0.2. The p-type AlInN hole injection layer 6 can be referred to as p-type Al... 1-q In q In the N-hole injection layer, the value of q ranges from 0.1 to 0.2. For example, q can be any value such as 0.1, 0.15, or 0.2.

[0050] When the InN composition is greater than 0.2, In will undergo severe phase separation and precipitation, leading to the deterioration of the quality of the p-type AlInN hole injection layer 6 and subsequent epitaxial structures.

[0051] The thickness of the p-type AlInN hole injection layer 6 is generally greater than 10 nm to form an effective tunnel junction. The specific thickness of the p-type AlInN hole injection layer 6 can be set by the user.

[0052] In one embodiment of this application, the thickness of the p-type AlInN hole injection layer 6 can be in the range of 10nm to 50nm. For example, the thickness of the p-type AlInN hole injection layer 6 can be 10nm, 20nm, 30nm, 40nm, 50nm, etc.

[0053] Since holes are left in the AlInN valence band after electrons tunnel through the p-type AlInN valence band to the n-type AlInN conduction band, an excessively thick p-type AlInN hole injection layer 6 is not needed to provide holes. An excessively thick p-type AlInN hole injection layer 6 will increase the epitaxial layer resistance. At the same time, when the AlInN thickness is greater than 100 nm, the surface roughness will increase with the increase of film thickness, which will affect the subsequent epitaxial layer growth quality.

[0054] The intrinsically polarized AlGaN layer 7 is an undoped Al m Ga 1-m In the N-layer, the value of m can be determined based on the composition of InN in the p-type AlInN hole injection layer 6 and the n-type AlInN layer 8.

[0055] It should be noted that the thickness of the intrinsically polarized AlGaN layer 7 is not limited in this application and depends on the circumstances.

[0056] As one possible implementation, the thickness of the intrinsically polarized AlGaN layer 7 is in the range of 6nm to 12nm. For example, the thickness of the intrinsically polarized AlGaN layer 7 can be 6nm, 8nm, 10nm, 12nm, etc.

[0057] The tunneling probability of a tunnel knot can be approximated by Wentzel–Kramers–Brillouin (WKB):

[0058] (1)

[0059] Among them, P t W is the electron tunneling probability. d Let m* be the width of the tunnel junction depletion region, m* be the effective mass of the electron, and E be the value of the electron. g Let be the bandgap of the material, ħ be the reduced Planck constant, q be the electron charge, and x be the real space coordinates of the electron at the tunnel junction barrier.

[0060] From formula (1), we can see that W d The smaller the value, the lower the electron tunneling probability P. t To increase the tunneling probability of the tunnel junction, the depletion region width should be reduced. However, when the depletion region width is too small, if the conduction band bottom of the n-region is higher than the valence band top of the p-region under zero bias, an additional bias voltage needs to be applied to make the conduction band bottom of the n-region flush with the valence band top of the p-region to open the tunneling channel, increasing the turn-on voltage of the tunnel junction and the overall turn-on voltage of the device. Therefore, the depletion region width needs to be minimized as much as possible without increasing the turn-on voltage. Therefore, the thickness of the intrinsically polarized AlGaN layer 7 is set between 6nm and 12nm.

[0061] The dopant in the heavily doped n-type AlInN layer 8 is Si atoms, with a doping concentration of 1×10⁸. 19 cm -3 The above is referred to as heavy doping.

[0062] It should be noted that this application does not limit the specific doping concentration in the heavily doped n-type AlInN layer 8, and the doping concentration is within the range of 1×10⁸. 19 cm -3 That's all.

[0063] As one possible implementation, the doping concentration in the n-type AlInN layer 8 can be in the range of 5 × 10⁸. 19 ~1×10 20 cm -3 .

[0064] It should be noted that this application does not limit the composition of InN in the n-type AlInN layer 8, and it can be set by the user.

[0065] As one possible implementation, the InN content in the n-type AlInN layer 8 can be in the range of 0.1~0.2. The n-type AlInN layer 8 can be denoted as n-type Al... 1-r In r For layer N, the value of r ranges from 0.1 to 0.2. For example, r can be any value such as 0.1, 0.15, or 0.2.

[0066] When the InN content is greater than 0.2%, In will undergo severe phase separation, leading to a deterioration in the quality of the n-type AlInN layer and the epitaxial structure.

[0067] The thickness of the n-type AlInN layer 8 is generally greater than 10 nm to form an effective tunnel junction. The specific thickness of the n-type AlInN layer 8 can be set by the user.

[0068] As one possible implementation, the thickness of the n-type AlInN layer 8 can be in the range of 10nm to 100nm. For example, the thickness of the n-type AlInN layer 8 can be 10nm, 30nm, 50nm, 70nm, 90nm, 100nm, etc.

[0069] When the thickness of the n-type AlInN layer 8 is less than 10 nm, it will result in the inability to form an effective tunnel junction. When the thickness of the n-type AlInN layer 8 is greater than 100 nm, the thicker the layer, the worse the quality of the n-type AlInN layer 8.

[0070] In this embodiment, the epitaxial structure employs tunnel junction technology. The tunnel junction layer comprises a heavily doped p-type AlInN hole injection layer 6, an intrinsically polarized AlGaN layer 7, and a heavily doped n-type AlInN layer 8. Specifically, the hole injection layer material in the epitaxial structure of this application is AlInN. Under the same bandgap width, AlInN has a larger lattice constant, intrinsic polarization, and piezoelectric polarization than AlGaN. Therefore, the heavily doped AlInN hole injection layer can generate a higher density of polarized surface charge at the interface with the intrinsically polarized AlGaN layer 7 compared to the heavily doped AlGaN hole injection layer. This increases the electric field strength in the space charge region of the tunnel junction, strengthens the band bending in the space charge region, promotes carrier tunneling, and improves the electrical performance and wall insertion efficiency of the epitaxial structure. Furthermore, during high-temperature growth, In atoms have a high vapor pressure at high temperatures and easily volatilize from the growth surface. This results in lower solubility of In atoms in the crystal lattice compared to Mg atoms, making it easier for Mg atoms to remain in the crystal. This effectively suppresses Mg precipitation and increases the Mg doping concentration. Because the doping concentration in the p-type AlInN hole injection layer 6 is increased, the thickness of the p-type AlInN hole injection layer 6 can be reduced in this application, thereby reducing the resistance.

[0071] The high solubility of Mg in the epitaxial structure based on the AlInN hole injection tunneling layer in this application is explained below.

[0072] The advantages of AlInN in inhibiting Mg precipitation and memory effect can be demonstrated through first-principles calculations.

[0073] The structure and total energy of the crystal were optimized using the first-principles density functional theory (DFT) program in the VASP (Vienna Ab-initio Simulation Package) software package. In the calculations, electron-ion interactions were performed using a projector-aumented plane wave (PAW) potential, while electron-electron exchange correlation interactions were described using the Perdeu-Burke-Enzerhof generalized gradient approximation (PBE-GGA) with a cutoff energy of 520 eV. Integrals in the Brillouin zone were performed using the Gamma-centered Monkhorst-Pack method (sampling the Monkhorst-Pack calculation points centered on the first Brillouin zone Γ of the unit cell), applying the Al 3s... 2 4s 1 Ga 3d 10 4s 2 4p 1 In 4d 10 5s 2 5p 1 and N 2s 2 2p 3 Valence electrons are considered in the calculation.

[0074] wurtzite supercell model, such as Figure 2 As shown, it contains 128 atoms to avoid Mg interactions in adjacent supercells. The k-point grid density is 3×3×3. The convergence criterion for the Hellman-Feynman force on each atom is 0.001 eV / Å, and the total energy convergence criterion is 10. -8 eV.

[0075] The enthalpy of impurity formation can be calculated using the following formula:

[0076] (2)

[0077] In the formula, ΔH is the total energy calculated for a supercell containing one impurity or defect D, also known as the impurity formation enthalpy; E D It is the total energy of the equivalent supercell of the doped material; E H It is the total energy of the equivalent supercell of the undoped material; n i This indicates that when a defect or impurity occurs, it is added to (n i <0) or remove (n) from the supercell i The number of the i-th type of host atom or impurity atom (>0); μ i These are the corresponding chemical potentials of these species.

[0078] The chemical potentials of Al, Ga, and In can be obtained from the lowest energy elemental materials, while the chemical potential of N can be obtained from N₂. The chemical potentials of binary nitrogen compounds satisfy the following conditions:

[0079] (3)

[0080] In the formula, μ III For the atomic chemical potential of group III elements, μ N For the chemical potential of the N atom, is the chemical potential of a dinitrogen compound.

[0081] Similarly, for ternary compound A 1-x B x The chemical potential of N (both A and B are group III elements) satisfies:

[0082] (4)

[0083] In the formula, For ternary compound A 1-x B x The chemical potential of N, μ A For the chemical potential of atom A, μ B For the chemical potential of the B atom, μ N Let x be the chemical potential of the N atom, and let x be the mole fraction of BN.

[0084] The enthalpy of Mg impurity formation in AlGaN / AlInN with different GaN / InN molar fractions was calculated, such as... Figure 3 As shown, the upper x-axis is Al. 1-x Ga x The mole fraction x of GaN in N; the lower x-axis represents Al. 1-x In x The mole fraction x of InN in N; the ordinate is the enthalpy of impurity formation ΔH. From Figure 3 It is known that, under the same bandgap width, AlInN has a lower impurity substitution formation energy ΔH than AlGaN. This allows for more stable and higher concentration of p-type doping in heavily doped p-type AlInN layers within tunnel junctions, resulting in higher hole concentrations while suppressing the memory effect of Mg.

[0085] Because the number of group III atoms in the supercell constructed for first-principles calculations is limited, it is not possible to construct AlInN and AlGaN with completely equal band gaps. Here, we use Al0.5Ga0.5N and Al0. 85 In0. 15 Taking N as an example for modeling, the bandgap value of Al0.5Ga0.5N is 4.97eV, and Al0. 85 In0. 15The band gap of N is 4.8 eV, and the band gaps of both are similar. The difference in solubility between the two is calculated, and their correlation with Al is also calculated. 0.4 Ga 0.6 Interfacial polarization charges generated by the N-polarization layer.

[0086] The number of Al sites and Ga sites N in Al0.5Ga0.5N at 1300K Al =N Ga =2.26×10 22 cm -3 Mg in N-rich environment Ga The impurity formation enthalpy is 1.559 eV, Mg Al The defect formation enthalpy is 1.656 eV. At 1150 K, Al0.05... 85 In0. 15 N in Al site N Al =3.79×10 22 cm -3 In site N In =6.69×10 21 cm -3 Mg in N-rich environment In The defect formation enthalpy is 1.232 eV, Mg Al The impurity formation enthalpy is 1.483 eV.

[0087] Under thermodynamic equilibrium, the solubility of semiconductor impurities is:

[0088] (5)

[0089] In the formula, S represents the solubility of semiconductor impurities, and N... sites ΔH represents the number of sites that an impurity can absorb per unit volume, k is the Boltzmann constant, T is the thermodynamic temperature, and ΔH is the enthalpy of impurity formation.

[0090] By calculating the enthalpy of Mg formation in the material, and substituting it into the above formula (5), the solubility of the impurity atoms in the material can be calculated.

[0091] Taking AlInN as an example, considering the solubility obtained by replacing Al with Mg and the solubility obtained by replacing In with Mg respectively, the total solubility can be expressed as:

[0092] (6)

[0093] In the formula, This represents the total solubility of Mg atoms in AlInN crystals. The enthalpy is formed by Mg replacing impurities at In sites in the crystal lattice. The enthalpy of formation for impurities at Al sites in the Mg lattice, N InN represents the number of In sites per unit volume of AlInN crystal. Al denoted as the number of Al sites per unit volume of AlInN crystal, k is the Boltzmann constant, and T is the thermodynamic temperature.

[0094] It is worth noting that nitride epitaxy in MOCVD (Metal-organic Chemical Vapor Deposition) is generally a non-equilibrium growth process. Although the concentration of Mg in the material cannot be directly obtained, the concentration of Mg in the two materials can be compared by comparing the solubility of Mg in each material.

[0095] (7)

[0096] In the formula, This represents the concentration of Mg atoms in the AlInN crystal. The solubility of Mg atoms in AlInN crystals. This represents the concentration of Mg atoms in the AlGaN crystal. The value represents the solubility of Mg atoms in AlGaN crystals.

[0097] Substituting the above calculation data, we can obtain Al. 0.85 In 0.15 N and Al 0.5 Ga 0.5 The ratio of Mg solubility in N is 0.747.

[0098] The tunneling performance advantages of the extensional structure based on the AlInN hole injection tunneling layer in this application are explained below.

[0099] Calculate Al 1-x In x N / Al 1-y Ga y N and Al 0.4 Ga 0.6 The interfacial polarization charges of N, from the c-axis direction, are Al 1- x In x N / Al 1-y Ga y N, Al 0.4 Ga 0.6 N. The polarization surface charge density is determined by the total polarization of the two layers of material:

[0100] (8)

[0101] In the formula, For Al 0.15 In 0.85 N or Al0.5 Ga 0.5 The total polarization intensity of N, For Al 0.4 Ga 0.6 The total polarization intensity of N, This represents the polarization surface charge density.

[0102] Total polarization intensity includes spontaneous polarization intensity and piezoelectric polarization intensity:

[0103] (9)

[0104] In the formula, P is the total polarization intensity; P sp Spontaneous polarization intensity, expressed in C / m. 2 ;P pz It represents the piezoelectric polarization intensity.

[0105] Based on Vegard's Law, Al 1-x In x N / Al 1-x Ga x The spontaneous polarization magnitude of N material is: (based on literature data Bernardini et al., 2001):

[0106] (10)

[0107] (11)

[0108] Among them, P sp The value of (AlN) is -0.081 C / m 2 P sp The value of (GaN) is -0.029 C / m 2 P sp The value of (InN) is -0.032 C / m 2 The negative sign indicates that the direction is opposite to the c-axis. The calculated Al... 0.85 In 0.15 N of P sp The value is -0.07365 C / m 2 Al 0.5 Ga 0.5 N of P sp The value is -0.0498 C / m 2 Al 0.4 Ga 0.6 N of P sp The value is -0.0498 C / m 2 .

[0109] Piezoelectric polarization P pz It can be expressed as the piezoelectric modulus e ij(The piezoelectric modulus of wurtzite crystals is represented by a matrix, where i and j represent the elements in the i-th row and j-th column of the matrix, respectively. The matrix elements are determined by the material.) and the strain tensor ε f (where f is the f-th basis vector in the lattice and ε is the strain tensor) functional relationship, for wurtzite crystals, the piezoelectric polarization can be expressed as:

[0110] (12)

[0111] In the formula, ε1, ε2, and ε3 are the strain tensor variables of lattice constants a, b, and c relative to the relaxed lattice constants a0, b0, and c0, respectively. This represents the piezoelectric modulus of the element in the 3rd row and 3rd column. This is the piezoelectric modulus of the element in the 3rd row and 1st column.

[0112] Among them, e 31 (Al 0.85 In 0.15 The value of N) is -0.5955 C / m², e 31 (Al 0.5 Ga 0.5 The value of N) is -0.49 C / m², e 31 (Al 0.4 Ga 0.6 The value of N) is -0.534 C / m²; e 33 (Al 0.85 In 0.15 The value of N) is 1.3865 C / m², e 33 (Al 0.5 Ga 0.5 The value of N) is -0.49 C / m², e 33 (Al 0.4 Ga 0.6 The value of N) is 1.022 C / m².

[0113] Assume Al 1-x In x N / Al 1-x Ga x The N thin layer is in a fully relaxed state, and Al can be calculated. 0.85 In 0.15 N and Al 0.4 Ga 0.6 The interfacial charge density of N is -0.018 C / m²; Al 0.5 Ga 0.5 N and Al 0.4 Ga 0.6 The interfacial charge density of N is -0.002 C / m². It is evident that Al... 0.85 In 0.15 N and Al0.4 Ga 0.6 N has a very high interfacial charge density, which can effectively enhance carrier tunneling.

[0114] Please refer to Figure 4 Based on the above embodiments, in one embodiment of this application, the epitaxial structure based on the AlInN hole injection tunneling layer may further include:

[0115] An electron blocking layer 9 is located between the multi-quantum well layer 5 and the tunnel junction layer.

[0116] Electron blocking layer 9 is a p-type doped film, and electron blocking layer 9 can be a p-type Al 1-k Ga k In layer N, the value of k ranges from 0.65 to 0.8, and the thickness of electron blocking layer 9 can be 10 nm.

[0117] The electron blocking layer 9 can prevent electrons from leaking from the active region to the p-type region, thereby improving the internal quantum efficiency and thus enhancing the electrical performance of the epitaxial structure.

[0118] Based on any of the above embodiments, in one embodiment of this application, the epitaxial structure based on the AlInN hole injection tunneling layer may further include:

[0119] n-type Al located between n-type semiconductor layer 4 and multi-quantum-well layer 5 1-j Ga j N layers, where j can range from 0.5 to 0.6, the dopant can be Si atoms, and the doping concentration can be 1 × 10⁻⁶. 19 ~5×10 19 cm -3 .

[0120] n-type Al 1-j Ga j The thickness of the N layer can be 50 nm.

[0121] In this embodiment, type n Al 1-j Ga j The N-layer, as an n-type electron deceleration layer, can suppress excessive electrons from entering the multi-quantum-well region, reduce the non-radiative recombination rate, and improve the electrical performance of the epitaxial structure.

[0122] like Figure 5 As shown, based on any of the above embodiments, in one embodiment of this application, the lattice constant of the intrinsically polarized AlGaN layer 7 is greater than the lattice constants of the p-type AlInN hole injection layer 6 and the n-type AlInN layer 8.

[0123] In this embodiment, the lattice constant of the intrinsically polarized AlGaN layer 7 is greater than that of the p-type AlInN hole injection layer 6 and the n-type AlInN layer 8, forming a compressive stress insertion layer. This results in the formation of polarized surface charges with opposite charge types at the interfaces on both sides of the intrinsically polarized AlGaN layer 7, which enhances the electric field in the space charge region of the tunnel junction and increases the tunneling probability.

[0124] In this embodiment, the lattice mismatch between the intrinsic polarized AlGaN layer 7 and the lattice constants of the p-type AlInN hole injection layer 6 and the n-type AlInN layer 8 is not limited and can be set by the user.

[0125] As one possible implementation, the lattice mismatch between the intrinsically polarized AlGaN layer 7 and the lattice constants of the p-type AlInN hole-injection layer 6 and the n-type AlInN layer 8 can be greater than 0.2% to obtain a sufficient amount of polarization surface charge.

[0126] like Figure 6 As shown, based on the above embodiments, in one embodiment of this application, the lattice constant of the intrinsically polarized AlGaN layer 7 is smaller than the lattice constant of the p-type AlInN hole injection layer 6 and the n-type AlInN layer 8.

[0127] In this embodiment, the lattice constants of the intrinsically polarized AlGaN layer 7 are all smaller than those of the p-type AlInN hole injection layer 6 and the n-type AlInN layer 8, forming a tensile stress insertion layer.

[0128] In this embodiment, the lattice mismatch between the intrinsic polarized AlGaN layer 7 and the lattice constants of the p-type AlInN hole injection layer 6 and the n-type AlInN layer 8 is not limited and can be set by the user.

[0129] As one possible implementation, the lattice mismatch between the intrinsic polarized AlGaN layer 7 and the lattice constants of the p-type AlInN hole injection layer 6 and the n-type AlInN layer 8 can be above 0.2% to obtain a sufficient amount of polarization surface charge. At the same time, the Al composition in the intrinsic AlGaN polarized layer under tensile stress is relatively high, which makes the intrinsic AlGaN polarized layer have a large resistance, which can promote the intra-epitaxy transport of charge carriers in the tunnel junction and suppress the current crowding effect.

[0130] This application also provides a deep ultraviolet optoelectronic device, which includes the epitaxial structure based on the AlInN hole injection tunneling layer described in any of the above embodiments.

[0131] This application does not limit the type of deep ultraviolet optoelectronic device. For example, a deep ultraviolet optoelectronic device can be a deep ultraviolet LED (light emitting diode).

[0132] The following section uses deep ultraviolet LEDs as an example to introduce the epitaxial structure based on the AlInN hole injection tunnel junction and the fabrication process of the deep ultraviolet optoelectronic device in this application.

[0133] Example

[0134] Step 1: Use acetone and isopropanol or methanol to ultrasonically clean the substrate surface for 5-10 minutes each time to remove organic matter and particles. The ultrasonic power should be controlled at 50-100 W and the temperature at 40-50°C. Then rinse with high-purity deionized water for 5 minutes.

[0135] Step 2: Place the substrate in a PVD (Physical Vapor Deposition) device and deposit an AlN buffer layer on the upper surface of the substrate.

[0136] Step 3: Adjust the temperature to 1000℃~1200℃ and grow an undoped periodic AlN / GaN film as a superlattice layer on the upper surface of the AlN buffer layer under a pressure of 50 torr~200 torr.

[0137] Step 4: Adjust the temperature to 1000℃~1100℃ and the pressure to 100~400 torr, and grow 2μm n-type Al on the upper surface of the superlattice layer. 0.5 Ga 0.5 N is used as the n-type semiconductor layer, and the n-type dopant is Si atoms;

[0138] Step 5: Adjust the temperature to 1000℃~1100℃ and grow 50nm n-type Al on the upper surface of the n-type semiconductor layer. 0.65 Ga 0.35 N-electronic deceleration layer;

[0139] Step 6: Grow a multi-quantum-well layer on the upper surface of the n-type electron deceleration layer. The multi-quantum-well layer includes three periods of Al. 0.4 Ga 0.6 N / Al 0.55 Ga 0.45 In an N-layer stacked structure with multiple quantum well layers, Al 0.4 Ga 0.6 The thickness of N is 2 nm, the growth temperature is 950℃~1050℃, and the pressure is 100 torr~500 torr; Al 0.55 Ga 0.45 The thickness of N is 10 nm, the growth temperature is 1000℃~1100℃, and the pressure is 100 torr~500 torr.

[0140] Step 7: Under an environment where the temperature is adjusted to 1050℃~1150℃ and the pressure is 100 torr~500 torr, grow an Al layer with a thickness of 10 nm on the upper surface of the multi-quantum well layer. 0.8 Ga 0.2 N electron blocking layer;

[0141] Step 8: Under an environment where the temperature is adjusted to 800℃~900℃ and the pressure is 750 torr~800 torr, grow a heavily doped p-type Al with a thickness of 10nm on the upper surface of the electron blocking layer. 0.85 In 0.15 N-hole injection layer, with Mg atoms as dopants;

[0142] Step 9: Adjust the temperature to 950℃~1050℃ and the pressure to 100 torr~500 torr in a heavily doped p-type Al environment. 0.85 In 0.15 Undoped Al with a thickness of 6 nm is grown on the upper surface of the N-hole injection layer. 0.4 Ga 0.6 N serves as the intrinsically polarized AlGaN layer;

[0143] Step 10: Under an environment where the temperature is adjusted to 850℃~880℃ and the pressure is 750 torr~800 torr, grow a heavily doped n-type Al with a thickness of 10 nm on the upper surface of the intrinsically polarized AlGaN layer. 0.85 In 0.15 The N-layer serves as the ohmic contact layer, marking the end of epitaxial growth.

[0144] Step 11: Place the epitaxial wafer in an environment filled with N2 for high-temperature annealing for 2 to 10 minutes to fully activate the p-type impurity atoms;

[0145] Step 12: Use ICP (Inductively Coupled Plasma) equipment to partially etch the ohmic contact layer in the epitaxial wafer until the n-type Al is exposed. 0.5 Ga 0.5 N layers form a stepped structure;

[0146] Step 13: Using electron beam evaporation technology, n-type Al under the etched and exposed epitaxial structure is... 0.5 Ga 0.5 Ti / Al / Ti / Au (20 nm / 100 nm / 20 nm / 100 nm) was deposited on the N layer as the n electrode and annealed at 900 °C in N2 atmosphere for 1 min to form an n-type ohmic contact.

[0147] Step 14: Deposit Ni / Au (50nm / 100 nm) as a p electrode on the n-type ohmic contact layer above the epitaxial structure using electron beam evaporation technology, and anneal at 600℃ in air atmosphere for 1 min to form a p-type ohmic contact;

[0148] Step 15: Cut the epitaxial structure to make a single deep ultraviolet LED chip with a size of 300μm×300μm.

[0149] Comparative Example 1

[0150] The deep ultraviolet LED chip based on the AlGaN hole injection tunnel junction layer is basically the same as the example, except that the heavily doped p-type Al in the example is replaced with the one from the previous example. 0.85 In 0.15 The N-hole injection layer is replaced with heavily doped p-type Al. 0.5 Ga 0.5 The N-hole injection layer is 10 nm thick, grown at a temperature of 1000–1100 °C and a pressure of 100–500 torr. The dopant is Mg, and the doping concentration is set to 7.47 × 10⁻⁶ based on the calculated solubility ratio. 19 cm -3 ; the heavily doped n-type Al in the examples 0.85 In 0.15 The N-hole injection layer was replaced with heavily doped n-type Al. 0.5 Ga 0.5 The N-hole injection layer is 10 nm thick, grown at a temperature of 1000–1100 °C and a pressure of 100–500 torr. The dopant is Si with a doping concentration of 7.47 × 10⁻⁶. 19 cm -3 .

[0151] Comparative Example 2

[0152] The tunnel junction-free deep ultraviolet LED chip is basically the same as the example, except that the hole injection tunnel junction layer in the example is replaced with p-type doped Al. 0.5 Ga 0.5 The N-hole injection layer is 100 nm thick, grown at a temperature of 1000℃~1100℃ and a pressure of 100 torr~500 torr. The dopant is Mg, and the doping concentration is set to 7.47 × 10⁻⁶ based on the calculated solubility ratio. 19 cm -3 ; In an environment where the temperature is adjusted to 850~950℃ and the pressure is 100 torr~500 torr, p-type doped Al 0.5 Ga 0.5A 10 nm thick p-type doped GaN contact layer was grown on the surface of the N-hole injection layer. Electron beam evaporation was used to grow the p-type doped Al... 0.5 Ga 0.5 Ni / Au (50 nm / 100 nm) was deposited on the N-contact layer as the p-electrode and annealed at 600 °C in air for 1 min.

[0153] APSYS was used to simulate the embodiments and comparative examples 1 and 2. The parameters set in the APSYS software simulation included: the carrier SRH (Shockley-Read-Hall) recombination coefficient was set to 1 × 10⁻⁶. -8 s, Auger composite coefficient is set to 1×10 -42 m 6 s -1 The ratio of conduction band difference to valence band difference (ΔE) C / ΔE V The polarization in the

[0001] direction is 40%, and the simulated ambient temperature is 300K. The advantages of the AlInN tunneling layer mentioned above can be attributed to... Figure 3 , Figure 7 , Figure 8 , Figure 9 , Figure 10 , Figure 11 reflect.

[0154] Figure 7 The horizontal axis represents voltage, and the vertical axis represents current. Figure 7 It can be seen that after reaching the turn-on voltage, the voltages of the two comparative examples are larger than those of the embodiment under the same current, indicating that the resistance of the device in the embodiment is lower than that of the comparative examples.

[0155] Figure 8 The horizontal axis represents current, and the vertical axis represents output power. Figure 8 It can be seen that, under the same current, the embodiment has a greater output power than the two comparative examples.

[0156] Figure 9 The horizontal axis represents current, and the vertical axis represents wall socket efficiency. Figure 9 It can be seen that, under the same current, the embodiment has a greater wall socket efficiency than the two comparative examples, and the embodiment is more efficient in converting electrical energy into light energy.

[0157] Figure 10 The horizontal axis represents the relative position in the vertical direction, and the vertical axis represents the radiative recombination rate. Figure 10 It can be seen that, under a current of 300mA, the radiative recombination rate in the quantum well of the embodiment is higher than that of the two comparative embodiments.

[0158] Figure 11The horizontal axis represents current, and the vertical axis represents internal quantum efficiency. Figure 11 It can be seen that the internal quantum efficiency of the two comparative examples and the three sets of devices in the embodiment is relatively small under the same current. The internal quantum efficiency of the embodiment is slightly smaller than that of comparative example 2, i.e., the traditional deep ultraviolet LED without a tunnel junction. This indicates that the device structure of the embodiment does not affect the injection of charge carriers after the application of the new tunnel junction.

[0159] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0160] The epitaxial structure and deep ultraviolet optoelectronic device based on the AlInN hole injection tunneling layer provided in this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the solution and core ideas of this application. It should be noted that those skilled in the art can make several improvements and modifications to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of this application.

Claims

1. An epitaxial structure based on an AlInN hole injection tunneling layer, characterized in that, include: A substrate, wherein a buffer layer, a superlattice layer, an n-type semiconductor layer, a multiple quantum well layer and a tunnel junction layer are sequentially stacked on the upper surface of the substrate in a direction away from the substrate, the tunnel junction layer comprising a heavily doped p-type AlInN hole injection layer, an intrinsically polarized AlGaN layer and a heavily doped n-type AlInN layer.

2. The epitaxial structure based on AlInN hole injection tunneling layer as described in claim 1, characterized in that, Also includes: An electron blocking layer located between the multi-quantum well layer and the tunnel junction layer.

3. The epitaxial structure based on AlInN hole injection tunneling layer as described in claim 1, characterized in that, The doping concentration range in the p-type AlInN hole injection layer is 5 × 10⁻⁶. 19 ~1×10 20 cm -3 .

4. The epitaxial structure based on AlInN hole injection tunneling layer as described in claim 1, characterized in that, The InN composition range in the p-type AlInN hole injection layer is 0.1~0.

2.

5. The epitaxial structure based on AlInN hole injection tunneling layer as described in claim 1, characterized in that, The doping concentration range in the n-type AlInN layer is 5 × 10⁻⁶. 19 ~1×10 20 cm -3 .

6. The epitaxial structure based on AlInN hole injection tunneling layer as described in claim 1, characterized in that, The InN composition in the n-type AlInN layer ranges from 0.1 to 0.

2.

7. The epitaxial structure based on AlInN hole injection tunneling layer as described in claim 1, characterized in that, The thickness of the p-type AlInN hole injection layer ranges from 10 nm to 50 nm; and / or, the thickness of the n-type AlInN layer ranges from 10 nm to 100 nm; and / or, the thickness of the intrinsically polarized AlGaN layer ranges from 6 nm to 12 nm.

8. The epitaxial structure based on AlInN hole injection tunneling layer as described in any one of claims 1 to 7, characterized in that, The lattice constants of the intrinsically polarized AlGaN layers are all greater than those of the p-type AlInN hole-injection layer and the n-type AlInN layer.

9. The epitaxial structure based on an AlInN hole injection tunneling layer as described in any one of claims 1 to 7, characterized in that, The lattice constants of the intrinsically polarized AlGaN layers are all smaller than those of the p-type AlInN hole-injection layer and the n-type AlInN layer.

10. A deep ultraviolet optoelectronic device, characterized in that, Including the epitaxial structure based on AlInN hole injection tunneling layer as described in any one of claims 1 to 9.

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