An epitaxial structure of a triple-junction solar cell and its manufacturing method

Abstract

This invention discloses an epitaxial structure of a triple-junction solar cell and its manufacturing method, comprising a first sub-cell, a second sub-cell, and a third sub-cell grown sequentially in layers; the second sub-cell includes an InGaAs base region, an InGaAs emitter region, a first back surface field layer, and a first window layer; the third sub-cell includes a GaInP base region, a GaInP emitter region, a second back surface field layer, and a second window layer; one or more of the first window layer, the second back surface field layer, and the second window layer are formed by multiple sets of alternately grown Al... x1 In 1‑x1 P layer, Al x2 In 1‑ x2 The superlattice structure consists of P layers, where 0.65 ≤ x1 ≤ 0.75, x2 = 0.4, and Al x1 In 1‑x1 Layer P is under tensile stress, Al x2 In 1‑x2 The P-layer is under compressive stress. In this application, the window layer and / or back field layer are set as a superlattice structure, which effectively improves the ability of the back field layer and / or window layer to confine charge carriers under high temperature environment while ensuring crystal quality.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device technology, and specifically relates to an epitaxial structure of a triple-junction solar cell and its manufacturing method. Background Technology

[0002] Spacecraft power systems are a crucial component of spacecraft, directly impacting their lifespan and mission performance. Triple-junction solar cells (GaInP / InGaAs / Ge) have become core components of spacecraft power systems due to their high photoelectric conversion efficiency and excellent radiation resistance. However, space solar cells differ from those used on Earth. They are subject to damage and degradation due to the complex space environment. Besides being affected by high-energy particle radiation, ambient temperature is a significant factor in the space operating environment, especially for spacecraft power systems near planets like Venus and Mercury. For instance, high temperatures intensify atomic thermal motion, increasing the kinetic energy of photogenerated carriers, making it easier for them to overcome interfacial barriers and migrate to the surface, undergoing non-radiative recombination. Simultaneously, high temperatures activate defects such as dangling bonds on material surfaces and interfaces, forming strong recombination centers, further exacerbating carrier loss and leading to a sharp decline in cell conversion efficiency.

[0003] To address these issues, conventional techniques employ wide-bandgap materials (such as AlInP and AlGaAs) as back-field and window layers on either side of the cell's absorption region to form a barrier, preventing carrier diffusion to the surface and passivating the interface. However, this approach has significant shortcomings at high temperatures: firstly, carrier kinetic energy increases significantly at high temperatures, rendering the barrier height formed by conventional wide-bandgap materials insufficient and weakening its confinement ability, resulting in continued severe efficiency degradation; secondly, simply increasing the bandgap of the back-field and window layers to form a higher barrier introduces mismatched dislocations in the epitaxial layer due to lattice constant mismatch. These dislocations act as strong recombination centers for carriers, severely impairing cell efficiency and negating the benefits of using wide-bandgap materials.

[0004] Therefore, how to effectively improve the carrier confinement capability of the back field layer and window layer under high temperature environment while ensuring crystal quality (avoiding mismatch dislocations) has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide an epitaxial structure for a triple-junction solar cell and its manufacturing method, which effectively improves the carrier confinement capability of the back field layer and / or window layer under high-temperature conditions while ensuring crystal quality.

[0006] To achieve the above objectives, the present invention provides an epitaxial structure for a triple-junction solar cell, comprising a first sub-cell, a second sub-cell, and a third sub-cell stacked sequentially; wherein, the second sub-cell includes an InGaAs base region, an InGaAs emitter region, a first back field layer below the InGaAs base region, and a first window layer above the InGaAs emitter region; the third sub-cell includes a GaInP base region, a GaInP emitter region, a second back field layer below the GaInP base region, and a second window layer above the GaInP emitter region;

[0007] One or more of the first window layer, the second back field layer, and the second window layer are composed of multiple sets of alternately grown Al. x1 In 1-x1 P layer, AlInP gradient layer, Al x2 In 1-x2 The superlattice structure consists of P layers, where 0.65 ≤ x1 ≤ 0.75, x2 = 0.4, and Al x1 In 1-x1 Layer P is under tensile stress, Al x2 In 1-x2 The P layer is under compressive stress; the Al composition of the AlInP graded layer gradually changes from x1 to x2 or from x2 to x1, and the doping concentration of the AlInP graded layer is higher than that of Al. x1 In 1-x1 P layer and Al x2 In 1-x2 The doping amount of the P layer, wherein the doping amount is the amount of N-type dopant or P-type dopant.

[0008] Furthermore, the Al x1 In 1-x1 P layer and Al x2 In 1-x2 The thickness of the P layer is 5 nm, the thickness of the AlInP gradient layer is 2 nm, and the number of alternating pairs of the superlattice structure is 4 to 8.

[0009] Furthermore, a stress-gradient layer is disposed above the superlattice structure, and the Al composition of the stress-gradient layer gradually changes from the end of the superlattice structure to the end of the adjacent sub-cell layer.

[0010] Furthermore, the Al x1 In 1-x1 The P layer is the first and last layer in the superlattice structure, and the Al composition of the stress-gradient layer gradually changes from x1 to 0.5.

[0011] Furthermore, the first window layer, the second backfield layer, and the second window layer are all composed of multiple sets of alternately grown Al. x1 In 1-x1P layer, AlInP gradient layer, Al x2 In 1-x2 The structure consists of a superlattice composed of P layers; the first and second window layers are both doped with N-type dopant Si, of which Al x1 In 1-x1 P layer and Al x2 In 1-x2 The doping concentration of the P layer is 1E. 18 cm -3 To 3E 18 cm -3 The doping concentration of the AlInP graded layer is 5E. 18 cm -3 Up to 6E 18 cm -3 The second back field layer is doped with p-type Zn, where Al... x1 In 1-x1 P layer and Al x2 In 1-x2 The doping concentration of the P layer is 1E. 18 cm -3 Up to 2E 18 cm -3 The doping concentration of the AlInP graded layer is 3E. 18 cm -3 Up to 4E 18 cm -3 .

[0012] Furthermore, stress gradient layers are provided above the first window layer, the second back field layer, and the second window layer, respectively, namely a first stress gradient layer, a second stress gradient layer, and a third stress gradient layer; wherein, the first stress gradient layer is made of AlInP, has a thickness of 50nm-100nm, and is doped with N-type Si with a doping amount of 1E. 18 cm -3 To 3E 18 cm -3 The second stress-gradient layer is made of AlInP, with a thickness of 50nm-100nm, and is doped with p-type Zn at a doping level of 1E. 18 cm -3 Up to 2E 18 cm -3 The third stress-gradient layer is made of GaAsP, with the P composition gradually decreasing from 10% to 0%, and its thickness is 50nm-100nm. The dopant element is N-type Si, with a doping amount of 1E. 18 cm -3 To 3E 18 cm -3 .

[0013] Furthermore, the first back field layer is an AlGaAs back field layer, wherein the Al composition accounts for 80%-90%, and the thickness of the first back field layer is 80nm-100nm. The doping element is the p-type dopant Zn, and the doping amount is 1E. 18 cm -3 .

[0014] Furthermore, the pn junction of the first sub-cell is formed by N-type phosphorus diffusion on the surface of a Ge substrate. Between the Ge substrate and the first back field layer, a GaInP nucleation layer, a GaAs buffer layer, a first tunneling junction layer, and a DBR layer are stacked sequentially, wherein the GaInP nucleation layer and the GaAs buffer layer serve as window layers for the first sub-cell; a second tunneling junction layer is provided between the second sub-cell and the third sub-cell.

[0015] This application also provides a method for manufacturing an epitaxial structure of a triple-junction solar cell, used to prepare the above-mentioned epitaxial structure, including:

[0016] A Ge substrate is provided, and a first sub-cell is formed on the Ge substrate;

[0017] A second sub-cell is grown on the first sub-cell. The second sub-cell includes an InGaAs base region, an InGaAs emitter region, a first back field layer grown below the InGaAs base region, and a first window layer grown above the InGaAs emitter region.

[0018] A third sub-cell is grown on the second sub-cell. The third sub-cell includes a GaInP base region, a GaInP emitter region, a second back field layer grown below the GaInP base region, and a second window layer grown above the GaInP emitter region.

[0019] During the growth of the second and third sub-cells, one or more of the first window layer, the second back field layer, and the second window layer are formed by multiple sets of alternately grown Al. x1 In 1-x1 P layer, AlInP gradient layer, Al x2 In 1-x2 The superlattice structure consists of P layers, where 0.65 ≤ x1 ≤ 0.75, x2 = 0.4, and Al x1 In 1-x1 Layer P is under tensile stress, Al x2 In 1-x2 The P layer is under compressive stress; the Al composition of the AlInP graded layer gradually changes from x1 to x2 or from x2 to x1, and the doping concentration of the AlInP graded layer is higher than that of Al. x1 In 1-x1 P layer and Al x2 In 1-x2The doping amount of the P layer, wherein the doping amount is the amount of N-type dopant or P-type dopant.

[0020] After adopting the above solution, the beneficial effects of the present invention are as follows:

[0021] 1. In this application, one or more of the following structures of the second sub-cell's window layer (i.e., the first window layer), the third sub-cell's back field layer, and the window layer (i.e., the second back field layer and the second window layer) are configured to be composed of alternating layers of Al x1 In 1-x1 P layer, Al x2 In 1-x2 A superlattice structure composed of P layers. Where 0.65 ≤ x1 ≤ 0.75, x2 = 0.4, high Al content Al x1 In 1-x1 The P-layer provides a wide bandgap, significantly increasing the barrier height, thus more effectively blocking the diffusion of high-energy charge carriers to the surface at high temperatures and improving the degradation of solar cell photoelectric conversion efficiency at high temperatures. Meanwhile, Al... x1 In 1-x1 Layer P is under tensile stress, Al x2 In 1-x2 Layer P is under compressive stress, Al x2 In 1-x2 The P layer can offset the high aluminum content (Al). x1 In 1-x1 The tensile stress introduced by the P layer reduces the net stress of the entire superlattice structure, effectively suppressing mismatch dislocations caused by lattice mismatch.

[0022] 2. This application is also in Al x1 In 1-x1 P layer and Al x2 In 1-x2 Setting highly doped AlInP gradient layers between P layers can effectively reduce the resistance caused by the superlattice structure and avoid performance degradation due to the high resistance of the superlattice structure.

[0023] 3. This application sets a stress gradient layer above the superlattice structure, which gradually changes the tensile stress from the superlattice structure to the normal stress, and smoothly releases the residual tensile stress in the superlattice region to a state that matches the subsequent epitaxial layer, thereby avoiding the impact of stress accumulation in the superlattice structure on the growth of the subsequent epitaxial layer. Attached Figure Description

[0024] Figure 1 This is an epitaxial structure diagram of the solar cell of the present invention.

[0025] Figure 2 This is a diagram of the superlattice structure of the present invention.

[0026] Figure 3This is a flowchart of the manufacturing method of the present invention.

[0027] Label Explanation:

[0028] 1. Ge substrate; 2. GaInP nucleation layer; 3. GaAs buffer layer; 4. First tunnel junction layer; 5. DBR layer; 6. First back field layer; 7. InGaAs base region; 8. InGaAs emitter region; 9. First window layer; 10. First stress gradient layer; 11. Second tunnel junction layer; 12. Second back field layer; 13. Second stress gradient layer; 14. GaInP base region; 15. GaInP emitter region; 16. Second window layer; 17. Third stress gradient layer; 18. GaAs ohmic contact layer; 19. Superlattice structure. Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application, and the range values ​​mentioned in this application all include endpoint values.

[0030] Key references Figures 1-2 The present invention provides an epitaxial structure for a triple-junction solar cell, comprising a first sub-cell, a second sub-cell, and a third sub-cell stacked sequentially; wherein, the second sub-cell includes an InGaAs base region 7, an InGaAs emitter region 8, a first back field layer 6 below the InGaAs base region 7, and a first window layer 9 above the InGaAs emitter region 8; the third sub-cell includes a GaInP base region 14, a GaInP emitter region 15, a second back field layer 12 below the GaInP base region 14, and a second window layer 16 above the GaInP emitter region 15.

[0031] One or more of the first window layer 9, the second back field layer 12, and the second window layer 16 are composed of multiple sets of alternating Al layers. x1 In 1-x1 P layer, AlInP gradient layer, Al x2 In 1-x2 The superlattice structure consists of 19 P-layers, where 0.65 ≤ x1 ≤ 0.75, x2 = 0.4. Higher Al content results in a wider band gap. x1 In 1-x1 The bandgap of the P-layer is Eg = 2.69 eV - 2.93 eV, Al x2 In 1-x2 The bandgap of the P-layer is Eg = 2.13 eV, thus Al x1In 1-x1 The P-layer provides a wide bandgap, significantly increasing the barrier height and thus more effectively blocking the diffusion of high-energy charge carriers to the surface at high temperatures, improving the degradation of solar cell photoelectric conversion efficiency at high temperatures. Meanwhile, Al... x1 In 1-x1 Layer P is under tensile stress, Al x2 In 1-x2 Layer P is under compressive stress, Al x2 In 1-x2 The P layer can offset the high aluminum content (Al). x1 In 1-x1 The tensile stress introduced by the P layer reduces the net stress of the entire superlattice structure 19, effectively suppressing mismatch dislocations caused by lattice mismatch. Furthermore, the Al composition of the AlInP graded layer gradually changes from x1 to x2 or from x2 to x1 to reduce the Al content. x1 In 1-x1 The P layer gradually transforms into Al. x2 In 1-x2 P layer, or Al x2 In 1-x2 The P layer gradually transforms into Al. x1 In 1-x1 The P-layer, and the doping concentration of N-type or P-type dopants in the AlInP graded layer is higher than that in Al. x1 In 1-x1 P layer and Al x2 In 1-x2 The P-layer is highly doped in Al. x1 In 1-x1 P layer and Al x2 In 1-x2 Setting highly doped AlInP gradient layers between P layers can effectively reduce the resistance caused by the superlattice structure 19 and avoid performance degradation due to the high resistance of the superlattice structure.

[0032] Specifically, the Al x1 In 1-x1 P layer and Al x2 In 1-x2 The thickness of the P layers is 5 nm, the thickness of the AlInP graded layer is 2 nm, the superlattice structure 19 has 4 to 8 alternation pairs, and the Al... x1 In 1-x1 The P-layers are the first and last layers in the superlattice structure 19, i.e., the superlattice structure 19 is based on Al. x1 In 1-x1 Starting with layer P, and also with layer Al x1 In 1-x1 The P-layer ends. Since a higher Al content corresponds to a lower refractive index, the low-refractive-index Al... x1 In1-x1 The p-layer, as the terminal layer of the superlattice structure 19, can reduce light refraction and improve photoelectric conversion efficiency. Furthermore, due to Al... x1 In 1-x1 The P layer is a key functional layer for achieving wide bandgap and high barrier properties, and the outermost layer of the window layer or back field layer is the sensitive interface that needs to be protected, with Al as the core. x1 In 1-x1 Ending with a P-layer ensures that the barrier height is maximized at the most critical interface, providing the most effective carrier confinement.

[0033] Optional, although Al x2 In 1-x2 The P-layer can offset some of the tensile stress, but the superlattice structure 19 still exhibits tensile stress overall, which will affect the growth of subsequent epitaxial layers. Therefore, this application provides a stress-gradient layer above the superlattice structure 19. The material of the stress-gradient layer is AlInP, and the Al composition gradually changes from the end of the superlattice structure to the end of the adjacent sub-cell layer. Since the superlattice structure is based on Al... x1 In 1-x1 Ending with the P layer, the Al composition of the stress-gradient layer gradually changes from x1 to 0.5. That is, the stress-gradient layer gradually changes the tensile stress from the superlattice structure to the normal stress, and then smoothly releases the residual tensile stress in the superlattice region to a state that matches the subsequent epitaxial layer, avoiding the influence of stress accumulation in the superlattice structure on the growth of the subsequent epitaxial layer.

[0034] In the first window layer 9, the second back field layer 12, and the second window layer 16, the more layers of superlattice structure 19 there are, the better the effect of restricting carrier diffusion. As a preferred embodiment, the first window layer 9, the second back field layer 12, and the second window layer 16 are all set as superlattice structure 19, and the doping amount of each layer is as follows:

[0035] The first window layer 9 and the second window layer 16 are both doped with N-type dopant element Si, wherein Al x1 In 1-x1 P layer and Al x2 In 1-x2 The doping concentration of the P layer is 1E. 18 cm -3 To 3E 18 cm -3 The doping concentration of the AlInP graded layer is 5E. 18 cm -3 Up to 6E 18 cm -3 The second back field layer 12 is doped with p-type dopant Zn, wherein Al x1 In 1-x1 P layer and Al x2 In 1-x2The doping concentration of the P layer is 1E. 18 cm -3 Up to 2E 18 cm -3 The doping concentration of the AlInP graded layer is 3E. 18 cm -3 Up to 4E 18 cm -3 .

[0036] Optionally, a stress gradient layer is provided above the first window layer 9, the second back field layer 12, and the second window layer 16, namely a first stress gradient layer 10, a second stress gradient layer 13, and a third stress gradient layer 17, respectively; wherein, the first stress gradient layer 10 is made of AlInP, has a thickness of 50nm-100nm, and is doped with N-type Si with a doping amount of 1E. 18 cm -3 To 3E 18 cm -3 The second stress-gradient layer 13 is made of AlInP with a thickness of 50nm-100nm, and is doped with p-type Zn at a doping level of 1E. 18 cm -3 Up to 2E 18 cm -3 The material of the third stress gradient layer 17 can be replaced by GaAsP to prevent the thicker AlInP material from absorbing the top cell spectrum. The GaAsP material can be etched away in subsequent chip manufacturing processes without affecting the top cell spectrum. The thickness of the third stress gradient layer 17 is 50nm-100nm, and its P composition gradually changes from 10% to 0%. The doping element is the N-type dopant Si, and the doping amount is 1E. 18 cm -3 To 3E 18 cm -3 .

[0037] Specifically, the InGaAs base region 7 is In z3 Ga 1-x1 The InGaAs base region has z3 = 0.01 and a thickness of 2000 nm - 2500 nm. The photoluminescence wavelength is 880 nm. The dopant element is p-type Zn, and the doping concentration is 5E. 17 cm -3 Gradient to 1E 16 cm -3 .

[0038] The InGaAs emitter region 8 is In z4 Ga 1-z4The InGaAs emitter region has a z4 = 0.01 and a thickness of 50 nm-200 nm. The dopant element is N-type Si with a doping concentration of 1E. 18 cm -3 To 3E 18 cm -3 .

[0039] The GaInP base region 14 is Ga y3 In 1-y3 The GaInP-based region has a thickness of 600 nm-800 nm, where 0.4 ≤ y3 ≤ 0.6, and the dopant element is the p-type dopant Zn, with a doping amount ranging from 1E. 18 cm -3 Gradient to 1E 17 cm -3 .

[0040] The GaInP emitter region 15 is Ga y4 In 1-y4 The GaInP emitter region has a thickness of 50 nm-150 nm, where 0.4 ≤ y4 ≤ 0.6, and the dopant element is N-type Si with a doping amount of 1E. 18 cm -3 Up to 2E 18 cm -3 .

[0041] Optionally, the first back field layer 6 is an AlGaAs back field layer, wherein the Al composition accounts for 80%-90%, and the thickness of the first back field layer 6 is 80nm-100nm, and the doping element is the p-type dopant Zn, with a doping amount of 1E. 18 cm -3 That is, the first back field layer 6 is a normal back field layer structure and is not set as a superlattice structure 19. Since the base region of the second sub-cell (i.e., the InGaAs base region 7) is thick, it is difficult for carriers to diffuse from the base region of the second sub-cell to the first back field layer 6. Therefore, the first back field layer 6 does not need to be set as a superlattice structure. However, the base region of the third sub-cell (i.e., the GaInP base region 14) is thin and carriers can diffuse easily. Therefore, the back field layer of the third sub-cell (i.e., the second back field layer 12) needs to be set as a superlattice structure.

[0042] Optionally, the pn junction of the first sub-cell is formed by N-type phosphorus diffusion on the surface of the Ge substrate 1. A GaInP nucleation layer 2, a GaAs buffer layer 3, a first tunneling junction layer 4 and a DBR layer 5 are sequentially stacked between the Ge substrate 1 and the first back field layer 6. A second tunneling junction layer 11 is provided between the second sub-cell and the third sub-cell.

[0043] Among them, the thickness of GaInP nucleation layer 2 is 20nm-50nm, and the thickness of GaAs buffer layer 3 is 200nm-300nm. These two layers serve as window layers for the first sub-cell and also as connecting layers between Ge substrate 1 and subsequent epitaxial layers.

[0044] The first tunneling junction layer 4 is composed of heavily N-type doped GaAs and heavily P-type doped GaAs, with a thickness of 10 nm-30 nm. The heavily N-type doped GaAs is doped with Te at a doping level of 1E. 19 cm -3 Up to 2E 19 cm -3 P-type heavily doped GaAs with C doping at a doping level of 1E 20 cm -3 Up to 2E 20 cm -3 The first tunneling junction 4 utilizes the tunneling effect to connect the first sub-cell to the second sub-cell.

[0045] The second tunneling junction layer 11 is composed of N-type heavily doped Ga. y1 In 1-y1 P and P-type heavily doped Al y2 Ga 1-y2 Composed of As, with a thickness of 10nm-30nm. Among them, N-type heavily doped Ga y1 In 1-y1 P-doped Si, with a doping level of 1E 19 cm -3 Up to 2E 19 cm -3 And 0.5≤y1≤0.6; P-type heavily doped Al y2 Ga 1-y2 As doped with C, the doping amount is 1E. 20 cm -3 Up to 2E 20 cm -3 And 0.4≤y2≤0.6. Similar to the first tunneling junction 4, the second tunneling junction 11 also utilizes the tunneling effect to connect the second sub-cell to the third sub-cell.

[0046] The DBR layer 5 is a mirror structure comprising an adjustable multilayer structure of two optical materials, with the optical thickness of each layer being one-quarter of the center wavelength of the reflection spectrum. The center wavelength of the DBR layer 5 is 880 nm, and it is composed of In... z1 Ga 1-z1 As、Al z2 Ga 1-z2As is formed by alternating growth of two materials, where z1 = 0.01, 0.6 ≤ z2 ≤ 1, and the number of alternation pairs is 15-20 pairs. The DBR layer 5 is doped with p-type Zn, with a doping amount of 1E. 18 cm -3 Up to 4E 18 cm -3 .

[0047] Optionally, a GaAs ohmic contact layer 18 is further provided above the third stress gradient layer 17. The GaAs ohmic contact layer 18 has a thickness of 500nm-800nm, and the doping element is N-type dopant Si with a doping amount of 3E. 18 cm -3 Up to 5E 18 cm -3 .

[0048] This application also provides a method for manufacturing an epitaxial structure of a triple-junction solar cell, specifically using organic chemical vapor deposition (MOCVD) to grow the aforementioned epitaxial structure, with particular reference to... Figure 3 The preparation method includes the following steps:

[0049] S1. Provide a Ge substrate 1, wherein the Ge substrate 1 is a 9-degree P-type Ge substrate. Perform N-type phosphorus diffusion on the 9-degree P-type Ge substrate to diffuse the outermost Ge into N-type, thereby obtaining the pn junction of the Ge sub-cell. Then, grow a GaInP nucleation layer 2 and a GaAs buffer layer 3 that match the Ge lattice in sequence, with growth thicknesses of 20nm-50nm and 200nm-300nm, respectively. These two layers serve as window layers for the Ge sub-cell and also as connecting layers between the Ge substrate 1 and the subsequent epitaxial layers, thereby completing the fabrication of the first sub-cell.

[0050] S2. A first tunneling junction layer 4 is grown on the first sub-cell. The first tunneling junction layer 4 is composed of heavily N-type doped GaAs and heavily P-type doped GaAs, with a growth thickness of 10nm-30nm. Among them, the heavily N-type doped GaAs is doped with Te, and the doping amount is 1E. 19 cm -3 Up to 2E 19 cm -3 P-type heavily doped GaAs with C doping at a doping level of 1E 20 cm -3 Up to 2E 20 cm -3 .

[0051] S3. A DBR layer 5 is grown on the first tunneling junction layer 4, wherein the DBR layer 5 is composed of In z1 Ga 1-z1 As、Al z2 Ga1-z2 As is formed by alternating growth of two materials, where z1 = 0.01, 0.6 ≤ z2 ≤ 1, and the number of alternation pairs is 15-20 pairs. The center wavelength of DBR layer 5 is 880 nm, and the doping element is p-type dopant Zn with a doping amount of 1E. 18 cm -3 Up to 4E 18 cm -3 .

[0052] S4. Grow a second sub-cell on the DBR layer 5. The second sub-cell includes a first back field layer 6, an InGaAs base region 7, an InGaAs emitter region 8, a first window layer 9, and a first stress gradient layer 10, which are grown sequentially from bottom to top.

[0053] The first back field layer 6 is an AlGaAs back field layer, wherein the Al composition accounts for 80%-90%, and the growth thickness of the first back field layer 6 is 80nm-100nm. The doping element is the p-type dopant Zn, and the doping amount is 1E. 18 cm -3 .

[0054] The InGaAs base region 7 is In z3 Ga 1-x1 The InGaAs base region 7 has a growth thickness of 2000 nm-2500 nm, a photoluminescence wavelength of 880 nm, and is dominated by p-type Zn with a doping amount of 5E. 17 cm -3 Gradient to 1E 16 cm -3 .

[0055] The InGaAs emitter region 8 is In z4 Ga 1-z4 The InGaAs emitter region has a z4 = 0.01 and a growth thickness of 50 nm to 200 nm. The dopant element is N-type Si with a doping amount of 1E. 18 cm -3 To 3E 18 cm -3 .

[0056] The first window layer 9 consists of multiple groups of alternating Al layers. x1 In 1-x1 P layer, AlInP gradient layer, Al x2 In 1-x2 The structure consists of a superlattice 19 composed of P layers, where 0.65 ≤ x1 ≤ 0.75, x2 = 0.4, and the doping elements of the first window layer 9 are all N-type dopants, Si, including Al. x1 In1-x1 P layer and Al x2 In 1-x2 The doping concentration of the P layer is 1E. 18 cm -3 To 3E 18 cm -3 The doping concentration of the AlInP graded layer is 5E. 18 cm -3 Up to 6E 18 cm -3 .

[0057] The first stress gradient layer 10 is made of AlInP with a thickness of 50nm-100nm, and is doped with p-type Zn at a doping level of 1E. 18 cm -3 Up to 2E 18 cm -3 .

[0058] S5. A second tunneling junction layer 11 is grown on the second sub-cell, that is, the second tunneling junction layer 11 is grown on the first stress-gradient layer 10. The second tunneling junction layer 11 is made of N-type heavily doped Ga. y1 In 1-y1 P and P-type heavily doped Al y2 Ga 1-y2 The composition is As, and the growth thickness is 10nm-30nm. Among them, N-type heavily doped Ga y1 In 1-y1 P-doped Si, with a doping level of 1E 19 cm -3 Up to 2E 19 cm -3 And 0.5≤y1≤0.6; P-type heavily doped Al y2 Ga 1-y2 As doped with C, the doping amount is 1E. 20 cm -3 Up to 2E 20 cm -3 And 0.4≤y2≤0.6.

[0059] S6. A third sub-cell is grown on the second tunnel junction layer 11. The third sub-cell comprises a second back field layer 12, a second stress gradient layer 13, a GaInP base region 14, a GaInP emitter region 15, a second window layer 16, and a third stress gradient layer 17, which are grown sequentially from bottom to top.

[0060] The structure, material, and growth thickness of the second back field layer 12 are the same as those of the first window layer 9, and it is also set as a superlattice structure 19. The difference is that the doping element of the second back field layer 12 is the p-type dopant element Zn, in which Al x1 In 1-x1 P layer and Al x2 In 1-x2 The doping concentration of the P layer is 1E. 18 cm -3 Up to 2E 18 cm -3 The doping concentration of the AlInP graded layer is 3E. 18 cm -3 Up to 4E 18 cm -3 .

[0061] The structure, material, and growth thickness of the second stress gradient layer 13 are the same as those of the first stress gradient layer 10, except that the doping element of the second stress gradient layer 13 is the p-type dopant Zn, and the doping amount is 1E. 18 cm -3 Up to 2E 18 cm -3 .

[0062] The GaInP base region 14 is Ga y3 In 1-y3 The GaInP-based region has a growth thickness of 600 nm-800 nm, where 0.4 ≤ y3 ≤ 0.6, and the doping element is the p-type dopant Zn, with a doping amount ranging from 1E. 18 cm -3 Gradient to 1E 17 cm -3 .

[0063] The GaInP emitter region 15 is Ga y4 In 1-y4 The P-emitter region has a growth thickness of 50 nm-150 nm, where 0.4 ≤ y4 ≤ 0.6, and the dopant element is N-type Si with a doping amount of 1E. 18 cm -3 Up to 2E 18 cm -3 .

[0064] The structure, material, growth thickness, doping elements and doping amount of the second window layer 16 are the same as those of the first window layer 9.

[0065] The third stress gradient layer 17 is made of GaAsP, which prevents the thicker AlInP material from absorbing the top cell spectrum. Furthermore, the GaAsP material can be etched away after the GaAs ohmic contact layer 18 is grown, without affecting the top cell spectrum. The third stress gradient layer 17 has a growth thickness of 50nm-100nm, with its P composition gradually decreasing from 10% to 0%, and the doping element is N-type Si with a doping amount of 1E. 18 cm-3 To 3E 18 cm -3 .

[0066] S7. A GaAs ohmic contact layer 18 is grown on the third sub-cell. The GaAs ohmic contact layer 18 is grown on the third stress-gradient layer 17. The thickness of the GaAs ohmic contact layer 18 is 500nm-800nm, and the doping element is N-type dopant Si with a doping amount of 3E. 18 cm -3 Up to 5E 18 cm -3 .

[0067] It is worth noting that the thicknesses of the Ge substrate 1, GaInP nucleation layer 2, GaAs buffer layer 3, first tunneling junction layer 4, DBR layer 5, first back field layer 6, InGaAs base region 7, InGaAs emitter region 8, first window layer 9, first stress gradient layer 10, second tunneling junction layer 11, second back field layer 12, second stress gradient layer 13, GaInP base region 14, GaInP emitter region 15, second window layer 16, third stress gradient layer 17, and GaAs ohmic contact layer 18 shown in the accompanying drawings are merely examples and do not represent their actual thicknesses. Furthermore, the actual proportions of the Ge substrate 1, GaInP nucleation layer 2, GaAs buffer layer 3, first tunnel junction layer 4, DBR layer 5, first back field layer 6, InGaAs base region 7, InGaAs emitter region 8, first window layer 9, first stress gradient layer 10, second tunnel junction layer 11, second back field layer 12, second stress gradient layer 13, GaInP base region 14, GaInP emitter region 15, second window layer 16, third stress gradient layer 17, and GaAs ohmic contact layer 18 are not as shown in the accompanying drawings and are for reference only.

[0068] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0069] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An epitaxial structure of a triple-junction solar cell, characterized by: The first sub-cell, the second sub-cell and the third sub-cell are sequentially stacked; the second sub-cell comprises an InGaAs base region, an InGaAs emitting region, a first back field layer located below the InGaAs base region and a first window layer located above the InGaAs emitting region; the third sub-cell comprises a GaInP base region, a GaInP emitting region, a second back field layer located below the GaInP base region and a second window layer located above the GaInP emitting region; One or more of the first window layer, the second back field layer and the second window layer are formed by a plurality of groups of Al x1 In 1-x1 The P layer, the AlInP graded layer and the Al x2 In 1-x2 The superlattice structure is composed of the P layer, the AlInP graded layer and the Al x1 In 1-x1 The P layer is in tensile stress, the Al x2 In 1-x2 The P layer is in compressive stress; the Al component of the AlInP graded layer is graded from x1 to x2 or from x2 to x1, and the doping amount of the AlInP graded layer is higher than that of the Al x1 In 1-x1 The P layer and the Al x2 In 1-x2 The doping amount of the P layer is the doping amount of N-type or P-type doping elements.

2. An epitaxial structure for a triple-junction solar cell as recited in claim 1, wherein: The Al x1 In 1-x1 P layer and Al x2 In 1-x2 The thickness of the P layers is 5 nm, the thickness of the AlInP graded layer is 2 nm, and the number of the alternating pairs of the superlattice structure is 4 pairs to 8 pairs.

3. An epitaxial structure for a triple-junction solar cell as recited in claim 1, wherein: A stress gradient layer is arranged above the superlattice structure, and an Al component of the stress gradient layer gradually changes from an end of the superlattice structure to an end of an adjacent sub-cell layer.

4. An epitaxial structure for a triple-junction solar cell as set forth in claim 3, characterized by: The Al x1 In 1-x1 The P layer is the first and last layer in the superlattice structure, and the Al composition of the stress grading layer gradually changes from x1 to 0.

5.

5. An epitaxial structure for a triple-junction solar cell as described in claim 4, wherein: The first window layer, the second back field layer and the second window layer are all composed of a plurality of groups of alternately grown Al x1 In 1-x1 The P layer, the AlInP gradient layer, the Al x2 In 1-x2 P layer constitute a superlattice structure; the first window layer and the second window layer are both N-type doped elements Si, wherein the Al x1 In 1-x1 P layer and the Al x2 In 1-x2 The doping amount of the P layer is 1E 18 cm -3 to 3E 18 cm -3 , and the doping amount of the AlInP gradient layer is 5E 18 cm -3 to 6E 18 cm -3 ; the second back field layer is a P-type doped element Zn, wherein the Al x1 In 1-x1 P layer and the Al x2 In 1-x2 The doping amount of the P layer is 1E 18 cm -3 to 2E 18 cm -3 , and the doping amount of the AlInP gradient layer is 3E 18 cm -3 to 4E 18 cm -3 .

6. An epitaxial structure for a triple-junction solar cell as described in claim 5, wherein: The first window layer, the second back field layer and the second window layer are all provided with stress gradient layers, which are respectively a first stress gradient layer, a second stress gradient layer and a third stress gradient layer; wherein the material of the first stress gradient layer is AlInP, the thickness is 50nm-100nm, the doping element is N-type doping element Si, and the doping amount is 1E 18 cm -3 to 3E 18 cm -3 ; the material of the second stress gradient layer is AlInP, the thickness is 50nm-100nm, the doping element is P-type doping element Zn, and the doping amount is 1E 18 cm -3 to 2E 18 cm -3 ; the material of the third stress gradient layer is GaAsP, the P component in the GaAsP gradually changes from 10% to 0%, the thickness of the third stress gradient layer is 50nm-100nm, the doping element is N-type doping element Si, and the doping amount is 1E 18 cm -3 to 3E 18 cm -3 .

7. An epitaxial structure for a triple-junction solar cell as described in claim 1, wherein: the first, second, and third subcells are arranged in the order of the first subcell, the second subcell, and the third subcell. The first back field layer is an AlGaAs back field layer, wherein the Al component accounts for 80-90%, the thickness of the first back field layer is 80-100 nm, the doping element is a P-type doping element Zn, and the doping amount is 1E 18 cm -3 .

8. An epitaxial structure for a triple-junction solar cell as described in claim 1, wherein: the first, second, and third subcells are arranged in the order of the first subcell, the second subcell, and the third subcell. A pn junction of the first sub-cell is formed by N-type phosphorus diffusion on a surface of a Ge substrate, and a GaInP nucleation layer, a GaAs buffer layer, a first tunnel junction layer and a DBR layer are sequentially stacked between the Ge substrate and the first back field layer, wherein the GaInP nucleation layer and the GaAs buffer layer serve as a window layer of the first sub-cell; a second tunnel junction layer is arranged between the second sub-cell and the third sub-cell.

9. A method of manufacturing an epitaxial structure of a triple-junction solar cell, for producing an epitaxial structure of a junction solar cell according to any one of claims 1 to 8, characterized by, The method comprises: providing a Ge substrate, and forming a first sub-cell on the Ge substrate; growing a second sub-cell on the first sub-cell, wherein the second sub-cell comprises an InGaAs base region, an InGaAs emitting region, a first back field layer grown below the InGaAs base region and a first window layer grown above the InGaAs emitting region; growing a third sub-cell on the second sub-cell, wherein the third sub-cell comprises a GaInP base region, a GaInP emitting region, a second back field layer grown below the GaInP base region and a second window layer grown above the GaInP emitting region; and growing a third sub-cell on the second sub-cell, wherein the third sub-cell comprises a GaInP base region, a GaInP emitting region, a second back field layer grown below the GaInP base region and a second window layer grown above the GaInP emitting region; and In growing the second sub-cell and the third sub-cell, one or several of the first window layer, the second back field layer and the second window layer are composed of a plurality of groups of alternately grown Al x1 In 1-x1 P layer, AlInP gradient layer, Al x2 In 1-x2 P layer constitute a superlattice structure group, wherein 0.65≤x1≤0.75, x2=0.4, and Al x1 In 1-x1 P layer is tensile stress, Al x2 In 1-x2 P layer is compressive stress; the Al component of the AlInP gradient layer is gradually changed from x1 to x2 or from x2 to x1, and the doping amount of the AlInP gradient layer is higher than that of Al x1 In 1-x1 P layer and Al x2 In 1-x2 P layer, the doping amount is the doping amount of N-type or P-type doping elements.

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