A preparation method for an epitaxial wafer of a space-mismatch battery with a gradually varying base region composition

Abstract

The present invention discloses a preparation method for an epitaxial wafer of a space-mismatched cell with a gradually varying base region composition. Since the top cell and the middle cell are lattice mismatched with the substrate Ge, a buffer layer with a gradually varying composition and a certain thickness is required to eliminate the stress caused by the mismatch. The present invention discloses a preparation method for an epitaxial wafer of a space-mismatched cell with a gradually varying base region composition. It is to make the base region layer of the middle cell have a gradually varying composition, that is: in the present invention, the p-GaInAs base region layer of the middle cell of the space GaInP / InGaAs / Ge mismatched cell is divided into five gradually varying layers, and a transition layer with a gradually varying composition is deposited between the gradually varying layers. Compared with the conventional GaInP / InGaAs / Ge mismatched cell, the relatively thick buffer layer of the conventional mismatched cell is eliminated, thereby achieving the purpose of reducing costs. By optimizing the growth rate, thickness, and V / III ratio of the buffer layer, dislocations are reduced, and the recombination caused by the composition change is decreased, so as to achieve the optoelectronic conversion efficiency of the conventional mismatched structure.

Description

Technical Field

[0001] The present invention relates to a manufacturing method of battery epitaxial wafers, in particular to a preparation method of a spatially mismatched battery epitaxial wafer with a gradually varying base region composition. Background Art

[0002] Due to characteristics such as high photoelectric conversion efficiency and good anti-irradiation performance, GaAs solar cells are currently the main power source for space satellites. Conventional space GaAs solar cells are lattice-matched three-junction GaInP / InGaAs / Ge structures. Due to lattice matching, the dislocation density of the epitaxially grown material is relatively small, enabling the photoelectric conversion efficiency to reach about 30%. In order to further improve the photoelectric conversion efficiency, mismatched, inverted, and more-junction solar cells have emerged. The mismatched structure optimizes the bandgap combination of the middle cell and the top cell, resulting in a reduction in the bandgap widths of the middle cell and the top cell compared to lattice-matched cells. Therefore, it can absorb a wider spectrum, increase the current density of the entire cell, and improve the efficiency. Although the efficiency has been improved, it has also brought an increase in cost. In the mismatched structure, since the top cell and the middle cell are lattice-mismatched with the substrate Ge, a buffer layer with a gradually varying composition of a certain thickness is required to eliminate the stress caused by the mismatch, completely relax the growth of the middle cell, and reduce the recombination caused by the dislocations generated due to the mismatch. Similarly, the inverted structure also requires a buffer layer with a gradually varying composition of a certain thickness to eliminate the stress generated by the mismatch.

[0003] To improve the efficiency of space GaInP / InGaAs / Ge cells and control the cost of battery epitaxial wafers simultaneously, thinning or eliminating the buffer layer in the mismatched structure battery is one way. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for eliminating the buffer layer in a space GaInP / InGaAs / Ge mismatched structure battery and reducing the manufacturing cost of the mismatched battery.

[0005] The purpose of the present invention is achieved as follows:

[0006] A preparation method of a spatially mismatched battery epitaxial wafer with a gradually varying base region composition, characterized in that: a structure with a gradually varying composition is introduced into the GaInAs base region layer of the middle cell, and GaInAs base region layers with In compositions of 1.5%, 2%, 2.5%, 3%, and 3.5% are grown respectively, and a transition layer with a gradually varying composition and a thickness of 0.25 μm is grown between each GaInAs layer with different compositions. By optimizing the growth rate, thickness, and V / III ratio, the dislocation defects generated in the transition layer are reduced. The specific steps are as follows:

[0007] Provide a p-Ge substrate. Using MOCVD (Metal Organic Chemical Vapor Deposition), sequentially epitaxially grow an n-AlGaInP nucleation layer, an n-GaAs / n-GaInAs buffer layer, an n++-GaAs / p++-GaAs tunneling junction layer, a p-AlGaAs / p-AlGaInAs (DBR) reflection layer, a p-GaInP backfield layer, a p-GaInAs base region layer on the p-Ge substrate, then grow an n-GaInAs emitter region layer, an n-AlInP window layer, an n++-GaInP / p++-AlGaAs tunneling junction layer, a p-AlGaInP backfield layer, a p-GaInP base region layer, then grow an n-GaInP emitter region layer, an n-AlInP window layer, and an n+-GaAs ohmic contact layer.

[0008] The substrate material is p-Ge; the thickness of the n-AlGaInP nucleation layer is 0.01 μm, and the doping concentration is 1 - 2×10 18 cm -3 。

[0009] The thickness of the n-GaAs / n-GaInAs buffer layer is 0.5 μm, and the doping concentration is ≥1×10 18 cm -3 。

[0010] For the n++-GaAs / p++-GaAs tunneling junction layer, the thickness of the n++-GaAs layer is 0.01 - 0.03 μm, and the doping concentration is ≥5×10 18 cm -3 ; the thickness of the p++-GaAs layer is 0.01 - 0.03 μm, and the doping concentration is ≥1×10 19 cm -3 。

[0011] The thickness of the p-AlGaAs / p-AlGaInAs (DBR) reflection layer is 1.8 μm, and the doping concentration is 5×10 17 cm -3 。

[0012] The thickness of the p-GaInP backfield layer is 0.07 μm, and the doping concentration is 1 - 2×10 18 cm -3 。

[0013] The total thickness of the p-GaInAs base region layer is 2.5 μm, divided into five layers, each layer is 0.3 μm, and the doping concentration of each layer is 2 - 8×10 16 cm -3 ,In components are respectively Ga 0.985 In 0.015 As, Ga0.98 In 0.02 As, Ga 0.975 In 0.025 As, Ga 0.97 In 0.03 As, Ga 0.965 In 0.035 As. Four transition layers are grown between the five layers, each transition layer having a thickness of 0.25 μm. By controlling the flow rate of In, the composition of the transition layer gradually changes from the composition of the next lower layer to that of the next upper layer. The growth rate is 1 μm / h, and the doping concentration is 2 - 8×10 16 cm -3 .

[0014] The thickness of the n-GaInAs emitter layer is 0.1 μm, and the doping concentration is 1×10 18 cm -3 .

[0015] The thickness of the n-AlInP window layer is 0.1 μm, and the doping concentration is 1×10 18 cm -3 .

[0016] n++-GaInP / p++-AlGaAs tunneling junction layer, where the thickness of the n++-GaInP layer is 0.01 - 0.03 μm, and the doping concentration is ≥5×10 18 cm -3 , and the thickness of the p++-AlGaAs layer is 0.01 - 0.03 μm, and the doping concentration is ≥5×10 19 cm -3 .

[0017] The thickness of the p-AlGaInP backfield layer is 0.1 μm, and the doping concentration is 1 - 2×10 18 cm -3 .

[0018] The thickness of the p-GaInP base region layer is 0.9 μm, and the composition is Ga 0.49 In 0.51 P, and the doping concentration is 1 - 8×10 16 cm -3 .

[0019] The thickness of the n-GaInP emitter layer is 0.1 μm, and the doping concentration is 1×10 18 cm -3 .

[0020] The thickness of the n-AlInP window layer is 0.1 μm, and the doping concentration is 1×10 18 cm -3 .

[0021] The thickness of the n+-GaAs ohmic contact layer is 0.5 μm, and the doping concentration is greater than 5×10 18 cm -3 .

[0022] Compared with the conventional mismatch cell structure, the buffer layer in the conventional mismatch cell structure is not grown in the present invention. Instead, the composition grading is introduced into the base region of the middle cell. Five layers of composition-graded GaInAs grading layers are grown in the base region of the middle cell, and a transition layer with a gradually changing composition is grown between each grading layer. By optimizing the growth rate, thickness, and V / III ratio of the buffer layer, the dislocations are reduced, and the recombination caused by the composition change is decreased to achieve the photoelectric conversion efficiency of the conventional mismatch cell. Generally, a buffer layer of about 2 μm is required for the conventional mismatch cell, so this method can greatly reduce the cost of the mismatch cell structure. Brief Description of the Drawings

[0023] Figure 1 is a schematic diagram of the epitaxial layer structure related to the present invention.

[0024] Figure 2 is the base region layer structure of the middle cell GaInAs related to the present invention. The base region layer of GaInAs is composed of five layers of composition-graded layers, and a transition layer with a gradually changing composition is grown between every two graded layers.

[0025] The drawing reference numerals are as follows:

[0026] 100: P-type Ge substrate;

[0027] 101: n-AlGaInP nucleation layer;

[0028] 102: n-GaAs / GaInAs buffer layer;

[0029] 103: n++-GaAs / p++-GaAs tunneling junction layer;

[0030] 104: p-AlGaAs / p-AlGaInAs (DBR) reflection layer;

[0031] 105: p-GaInP back surface field layer;

[0032] 106: p-GaInAs base region layer;

[0033] 107: n-GaInAs emitter region layer;

[0034] 108: n-AlInP window layer;

[0035] 109: n++-GaInP / p++-AlGaAs tunneling junction layer;

[0036] 110: p-AlGaInP back surface field layer;

[0037] 111: p-GaInP base region layer;

[0038] 112: n-GaInP emitter region layer;

[0039] 113: n-AlInP window layer;

[0040] 114: n+-GaAs ohmic contact layer. Detailed implementation manners

[0041] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0042] The present invention will be further described in detail below with reference to examples and in conjunction with the accompanying drawings.

[0043] A preparation method for an epitaxial wafer of a space mismatch battery with a gradually changing base region composition uses a 2600G3 type MOCVD (Metal Organic Chemical Vapor Deposition) produced by AXITRON Company in Germany. The substrate is a p-Ge substrate, doped with a Ga source, with a concentration of 0.2E18 - 3E18 cm -3 , a thickness of 130 - 150 μm, and a 9° cut angle. The MO sources used are TMGa, TMAl, and TMIn, the doping sources used are CCl 4 , DEZn, and SiH 4 , and the special gases used are AsH 3 and PH 3 ;

[0044] The specific steps are as follows:

[0045] A. Pre-introduce PH 3 into the MOCVD reaction chamber, heat the reaction chamber to 690 °C, set the pressure to 230 mbar, and form an N-type doping with a concentration of 1×10 18 cm -3 on the surface of the p-Ge substrate through P diffusion to form a Ge sub-cell. Cool the reaction chamber to 620 °C, introduce the sources TMAI, TMGa, TMIn, and the special gas PH 3 , deposit an n-AlGaInP nucleation layer, the deposition thickness of the n-AlGaInP nucleation layer is 0.01 μm, and the doping SiH 4 source, with a doping concentration of 1 - 2×10 18 cm-3 ;

[0046] B. The pressure is increased to 450 mbar, the temperature of the reaction chamber is raised to 650 °C, and an n-GaAs / n-GaInAs buffer layer is deposited on the n-AlGaInP nucleation layer. The thickness of the n-GaAs / n-GaInAs buffer layer is 0.5 μm, and the doping source is SiH 4 , and the doping concentration is ≥ 1 × 10 18 cm -3 ;

[0047] C. The pressure of the reaction chamber is reduced to 50 mbar, and an n++-GaAs layer is deposited on the GaAs / GaInAs buffer layer at a temperature of 650 °C. The deposition thickness of the n++-GaAs layer is 0.01 - 0.03 μm, and the doping source is SiH 4 , and the doping concentration is ≥ 5 × 10 18 cm -3 . Then, a p++-GaAs layer is deposited on the n++-GaAs layer at a temperature of 620 °C. The thickness of the p++-GaAs layer is 0.01 - 0.03 μm, and the doping source is CCl 4 , and the doping concentration is ≥ 1 × 10 19 cm -3 ;

[0048] D. A p-AlGaAs / p-AlGaInAs (DBR) reflective layer is deposited on the p++-GaAs layer at a temperature of 650 °C. The thickness of the p-AlGaAs / p-AlGaInAs reflective layer is 1.8 μm, and the doping source is DEZn, and the doping concentration is 5 × 10 17 cm -3 ;

[0049] E. A p-GaInP backfield layer is deposited on the AlGaAs / AlGaInAs reflective layer at a temperature of 650 °C. The thickness of the p-GaInP backfield layer is 0.07 μm, and the doping source is DEZn, and the doping concentration is 1 - 2 × 10 18 cm -3 ;

[0050] F. A p-GaInAs base region layer is deposited on the GaInP backfield layer at a temperature of 650 °C. The p-GaInAs base region layer consists of nine layers with a total deposition thickness of 2.5 μm. Among them, each of the five graded layers has a thickness of 0.3 μm, and the In composition is Ga 0.985 In 0.015 As, Ga 0.98 In 0.02 As, Ga 0.975 In 0.025 As, Ga 0.97 In 0.03 As, Ga0.965 In 0.035 As, a doped DEZn source with a doping concentration of 2 - 8×10 16 cm -3 . A transition layer is grown between the graded layers, and the deposition thickness of each transition layer is 0.25 μm, and the doping concentration is 2 - 8×10 16 cm -3 . By controlling the linear gradient of the In flow rate through a flow meter, the composition of the transition layer gradually changes from the composition of the lower graded layer to the composition of the upper graded layer, with a growth rate of 1 μm / h, and the doped DEZn source and the doping concentration are both 2 - 8×10 16 cm -3 .

[0051] G. Deposit an n-GaInAs emitter layer on the p-GaInAs base region layer at a temperature of 650 °C. The thickness of the n-GaInAs emitter layer is 0.1 μm, and the doping concentration is 1×10 18 cm -3 ;

[0052] H. Deposit an n-AlInP window layer on the GaInAs emitter layer at a temperature of 650 °C. The deposition thickness of the n-AlInP window layer is 0.1 μm, and the doped SiH 4 source with a doping concentration of 1×10 18 cm -3 ;

[0053] I. Deposit an n++-GaInP / p++-AlGaAs tunneling junction layer on the AlInP window layer at a temperature of 620 °C. Among them: the deposition thickness of the n++-GaInP layer is 0.01 - 0.03 μm, and the doped SiH 4 source with a doping concentration of ≥5×10 18 cm -3 , and the thickness of the p++-AlGaAs layer is 0.01 - 0.03 μm, and the doped CCl 4 source with a doping concentration of ≥5×10 19 cm -3 ;

[0054] J. Deposit a p-AlGaInP backfield layer on the GaInP / AlGaAs tunneling junction layer at a temperature of 620 °C. The deposition thickness of the p-AlGaInP backfield layer is 0.1 μm, and the doped DEZn source with a doping concentration of 1 - 2×10 18 cm -3 ;

[0055] K. Deposit a p-GaInP base region layer on the AlGaInP backfield layer at a temperature of 630 °C. The composition is Ga 0.49 In 0.51P, with a thickness of 0.9 μm, doped with a DEZn source, and a doping concentration of 1 - 8×10 16 cm -3 ;

[0056] L. Deposit an n-GaInP emitter layer on the GaInP base region layer at a temperature of 630 °C. The deposited thickness of the n-GaInP emitter layer is 0.1 μm, doped with a SiH 4 source, and a doping concentration of 1×10 18 cm -3 ;

[0057] M. Deposit an n-AlInP window layer on the GaInP emitter layer at a temperature of 630 °C. The deposited thickness of the n-AlInP window layer is 0.1 μm, doped with a SiH 4 source, and a doping concentration of 1×10 18 cm -3 ;

[0058] N. Deposit an n+-GaAs ohmic contact layer on the AlInP window layer at a temperature of 630 °C. The deposited thickness of the n+-GaAs ohmic contact layer is 0.5 μm, doped with a SiH 4 source, and a doping concentration greater than 5×10 18 cm -3 .

[0059] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0060] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an epitaxial wafer of a spatially mismatched cell with a gradually varying base composition, characterized in that: In the new structure, the buffer layer in the conventional mismatched cell structure is not grown. A GaInAs layer with a gradually varying composition is deposited in the base region of the middle cell, and a transition layer with a gradually varying composition is grown between the gradually varying layers. The specific steps are as follows: Provide a p-Ge substrate, and use the metal organic chemical vapor deposition equipment of AXITRON Company to sequentially deposit an n-AlGaInP nucleation layer, an n-GaAs / n-GaInAs buffer layer, an n++-GaAs / p++-GaAs tunneling junction layer, a p-AlGaAs / p-AlGaInAs (DBR) reflection layer, a p-GaInP back field layer, a p-GaInAs base region layer, an n-GaInAs emitter region layer, an n-AlInP window layer, an n++-GaInP / p++-AlGaAs tunneling junction layer, a p-AlGaInP back field layer, a p-GaInP base region layer, an n-GaInP emitter region layer, an n-AlInP window layer, and an n+-GaAs ohmic contact layer on the p-Ge substrate; Deposit a p-GaInAs base region layer on the p-GaInP back field layer at a temperature of 650 °C. The p-GaInAs base region layer has a total of nine layers, and the total deposition thickness is 2.5 μm; Among them, each of the five graded layers is 0.3 μm thick, and the In composition is successively Ga0.985In 0.015 As, Ga 0.98 I n0.02 As, Ga 0.975 In 0.025 As, Ga 0.97 In 0.03 As, Ga 0.965 In 0.035 As, doped with a DEZn source, and the doping concentration is 2 - 8×10 16 cm -3 ; A transition layer is grown between the graded layers. The deposition thickness of each transition layer is 0.25 μm, and the doping concentration is 2 - 8×10 16 cm -3 ; The linear gradient of the In flow is controlled by a flow meter, so that the composition of the transition layer gradually changes from the composition of the lower graded layer to the composition of the upper graded layer. The growth rate is 1 μm / h, and the doped DEZn source and the doping concentration are both 2 - 8×10 16 cm -3 .

2. The method for preparing an epitaxial wafer of a spatially mismatched cell with a gradually varying base composition according to claim 1, characterized in that: The substrate material is a p-type Ge substrate, doped with a Ga source, and the doping concentration is 0.2E18 - 3E18 cm -3 , with a thickness of 130 - 150 μm and a 9° cut angle; The deposition thickness of the n-AlGaInP nucleation layer is 0.01 μm, doped with SiH 4 source, and the doping concentration is 1 - 2×10 18 cm -3 ; The deposition thickness of the n-GaAs / n-GaInAs buffer layer is 0.5 μm, doped with SiH 4 source, and the doping concentration is ≥1×10 18 cm -3 ; n++-GaAs / p++-GaAs tunneling junction layer, where the deposition thickness of the n++-GaAs layer is 0.01 - 0.03 μm, doped with SiH 4 source, doping concentration ≥ 5×10 18 cm -3 ; the deposition thickness of the p++-GaAs layer is 0.01 - 0.03 μm, doped with CCl 4 source, doping concentration ≥ 1×10 19 cm -3 ; The deposition thickness of the p-AlGaAs / p-AlGaInAs reflective layer is 1.8 μm, doped with DEZn source and the doping concentration is 5×10 17 cm -3 ; The deposition thickness of the p-GaInP back surface field layer is 0.07 μm, doped with a DEZn source and a doping concentration of 1 - 2×10 18 cm -3 ; The total thickness of the p-GaInAs base region layer deposited is 2.5 μm, which is divided into five compositionally graded layers, each with a thickness of 0.3 μm. A transition layer is deposited between the graded layers, and the thickness of each transition layer is 0.25 μm. The doping source is DEZn, and the doping concentration is 2 - 8×10 16 cm -3 ; The deposition thickness of the n-GaInAs emitter layer is 0.1 μm, doped with SiH 4 source, and the doping concentration is 1×10 18 cm -3 ; The deposition thickness of the n-AlInP window layer is 0.1 μm, doped with SiH 4 source, and the doping concentration is 1×10 18 cm -3 ; n++-GaInP / p++-AlGaAs tunneling junction layer, where the thickness of the deposited n++-GaInP layer is 0.01 - 0.03 μm and it is doped with SiH 4 source, and the doping concentration is ≥5×10 18 cm -3 ; the thickness of the deposited p++-AlGaAs layer is 0.01 - 0.03 μm and it is doped with CCl 4 source, and the doping concentration is ≥5×10 19 cm -3 ; The deposition thickness of the p-AlGaInP backfield layer is 0.1 μm, doped with a DEZn source and a doping concentration of 1 - 2×10 18 cm -3 ; The deposition thickness of the p-GaInP base region layer is 0.9 μm, and the composition is Ga 0.49 In 0.51 P, doped with DEZn source, and the doping concentration is 1 - 8×10 16 cm -3 ; The deposition thickness of the n-GaInP emitter layer is 0.1 μm, doped with SiH 4 source, and the doping concentration is 1×10 18 cm -3 ; The deposition thickness of the n-AlInP window layer is 0.1 μm, doped with SiH 4 source, and the doping concentration is 1×10 18 cm -3 ; The deposition thickness of the n+-GaAs ohmic contact layer is 0.5 μm, doped with SiH 4 The source and the doping concentration are greater than 5×10 18 cm -3 .

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