Method for preparing test samples of gallium arsenide solar cell multilayer epitaxial structure

Abstract

The application discloses a preparation method of a multi-layer epitaxial structure test sample of a gallium arsenide solar cell. Four test interfaces can be obtained through twice protection and corrosion, the preparation efficiency is improved, the sample damage probability is reduced by more than 30%, and multiple sample interfaces to be tested can be obtained at a time, so that various test requirements are met. Not only the growth quality of the four epitaxial layers can be visually observed, but also technical parameters such as the thickness of each related layer and the band gap width can be measured in addition to the component of the epitaxial layer and the ion doping concentration.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, and in particular to a method for preparing test samples of gallium arsenide solar cell multilayer epitaxial structures. Background Technology

[0002] Currently, gallium arsenide (GaAs) solar cells are widely used in the primary power systems of my country's spacecraft. GaAs solar cells are a type of III-V compound semiconductor solar cell. The main technology for researching and producing III-V compound solar cells is metal-organic vapor phase epitaxy (MOE). Its working principle involves introducing metal-organic compound gases such as tripotassium gallium (TMGa), tripotassium aluminum (TMAl), and tripotassium indium (TMIn), along with hydrides such as arsine and phosphine, into a vacuum chamber using H2. Under appropriate temperature conditions, various chemical reactions occur, generating III-V compounds such as GaAs, GaInP, and AlInP, which are then deposited on GaAs or Ge substrates to achieve epitaxial growth. During the research and development process, based on the test results of relevant epitaxial layer composition, ion doping concentration, thickness, and center wavelength, parameters such as epitaxial growth temperature, rate, and source flux are set and revised to ensure the growth quality of the epitaxial wafer.

[0003] Gallium arsenide (GaAs) solar cells offer numerous advantages, including high light absorption coefficient, good radiation resistance, low temperature coefficient, and the potential for higher efficiency. However, the material has relatively weak mechanical strength and is expensive. During development, due to operational costs, only 1-2 test wafers are grown per batch. The cost of growing a test epitaxial wafer on a 4-inch Ge or GaAs substrate is approximately 500-800 yuan, while the cost of a test wafer on a 2-inch GaN substrate is approximately 2000 yuan. Therefore, a single test wafer often serves multiple testing purposes. The preparation of epitaxial wafer test samples is particularly crucial. In the experimental phase, arsenides (such as GaAs, GaInAs, AlGaAs, etc.) and phosphides (GaInP, AlInP, AlGaInP, etc.) are alternately grown on different substrates using MOCVD technology, depending on the requirements. Later, depending on the etching solutions used for arsenides and phosphides, corresponding sample test interfaces are prepared, and then relevant tests are performed. The test results directly affect the setting of epitaxial growth process parameters.

[0004] Gallium arsenide solar cells generally use Ge and GaAs substrates, and GaN is also used in experiments. The thickness of Ge substrates is 145um to 175um, while GaAs substrates are slightly thicker. GaN is more brittle and easily broken. For test pieces with structures like Ga(In)As(1) / (Al)GaInP(2) / Ga(In)As(3) / (Al)GaInP(4) (or other alternating arsenide XXAs and phosphide XXP growth structures, such as (Al)GaInP(1) / Ga(In)As(2) / (Al)GaInP(3) / Ga(In)As(4)), sample preparation is particularly important if it is required to test the doping and composition of each layer. Generally, sample preparation is done by layer-by-layer protection and etching. Such four test interfaces generally require three protection and etching processes. However, sample breakage is very likely to occur during the application, removal, and rinsing of the blue film. Summary of the Invention

[0005] The purpose of this invention is to address the high cost of preparing test samples for gallium arsenide solar cell multilayer epitaxial structures in existing technologies, and to provide a low-cost method for preparing test samples. For epitaxial structures with alternating arsenide and phosphide growth, sample preparation is performed based on the principle that the same etching solution has the same effect on epitaxial layers of the same material.

[0006] The technical solution adopted to achieve the purpose of this invention is:

[0007] A method for preparing a test sample of a gallium arsenide solar cell multilayer epitaxial structure, wherein the sample before processing includes a substrate and a fourth epitaxial layer, a third epitaxial layer, a second epitaxial layer, and a first epitaxial layer deposited sequentially from bottom to top on the substrate, wherein the first epitaxial layer is exposed, and the other epitaxial layers are not exposed. The preparation method includes the following steps:

[0008] Step 1: Protect one side of the sample with the epitaxial layer with a protective film, leaving the other side exposed;

[0009] Step 2: Immerse the sample treated in Step 1 completely into the first etching solution to etch the exposed first epitaxial layer. After etching is completed, clean and dry it. At this time, the surface of the exposed area in Step 1 is the second epitaxial layer.

[0010] Step 3: Immerse the sample treated in Step 2 completely in the second etching solution to etch the second epitaxial layer. After etching is completed, clean and dry it. At this time, the exposed surface is the third epitaxial layer.

[0011] Step 4: Remove the protective film. The resulting sample has a third epitaxial layer on one side and a first epitaxial layer on the other side.

[0012] Step 5: Protect the side of the sample with the epitaxial layer again with a protective film, so that part of the third epitaxial layer and part of the first epitaxial layer are covered, and part of the third epitaxial layer and part of the first epitaxial layer are exposed;

[0013] Step 6: Immerse the sample treated in Step 5 completely in the third etching solution. The exposed third epitaxial layer and the first epitaxial layer are etched, exposing the fourth epitaxial layer and the second epitaxial layer respectively. Clean and dry.

[0014] Step 7: Remove the protective film. At this point, parts of the first to fourth epitaxial layers are exposed.

[0015] In the above technical solution, the substrate is a Ge substrate, a GaN substrate, or a GaAs substrate. When the substrate is a GaAs substrate, in step 1, a protective film is also needed to completely protect the side of the substrate that does not have an epitaxial layer.

[0016] In the above technical solution, the epitaxial structure is an epitaxial structure in which arsenide layers and phosphide layers are grown alternately, and the fourth epitaxial layer, the third epitaxial layer, the second epitaxial layer and the first epitaxial layer are respectively the fourth phosphide layer, the third arsenide layer, the second phosphide layer and the first arsenide layer.

[0017] Alternatively, the fourth epitaxial layer, the third epitaxial layer, the second epitaxial layer, and the first epitaxial layer may be a fourth arsenide layer, a third phosphide layer, a second arsenide layer, and a first phosphide layer, respectively.

[0018] In the above technical solution, the arsenide layer is a GaAs or GaInAs layer, and the phosphide layer is a GaInP layer, an AlInP(4) layer, or an AlGaInP layer.

[0019] In the above technical solution, the protective film in steps 1 and 5 is an acid- and alkali-resistant PVC film.

[0020] In the above technical solution, when the fourth epitaxial layer, the third epitaxial layer, the second epitaxial layer, and the first epitaxial layer are respectively the fourth phosphide layer, the third arsenide layer, the second phosphide layer, and the first arsenide layer, the first etching solution in step 2 and the third etching solution in step 6 are both mixed solutions of hydrogen peroxide and ammonia, and the second etching solution in step 3 is concentrated hydrochloric acid.

[0021] In the above technical solution, when the fourth epitaxial layer, the third epitaxial layer, the second epitaxial layer, and the first epitaxial layer are respectively the fourth arsenide layer, the third phosphide layer, the second arsenide layer, and the first phosphide layer, the first etching solution in step 2 and the third etching solution in step 6 are both concentrated hydrochloric acid; the second etching solution in step 3 is a mixed solution of hydrogen peroxide and ammonia.

[0022] In the above technical solution, the cleaning and drying in steps 2, 3 and 6 are all carried out by repeatedly rinsing with deionized water and then drying with compressed air.

[0023] In the above technical solution, in step 1, the protective film is applied to half of the sample with the epitaxial layer, while the other half is exposed. Preferably, the protective film is applied to the left half of the sample, while the right half is exposed.

[0024] In the above technical solution, in step 6, a protective film is applied to half of the sample with the epitaxial layer. Preferably, the protective film is applied to the upper half of the sample, while the lower half is exposed, so that half of the third epitaxial layer and half of the first epitaxial layer are covered, and half of the third epitaxial layer and half of the first epitaxial layer are exposed.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] The sample preparation method of the present invention only requires two protection and etching processes, which not only improves the preparation efficiency but also reduces the probability of sample breakage by more than 30%, achieving multiple benefits at once. It can simultaneously obtain multiple sample interfaces to be tested, meeting various testing needs. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the epitaxial growth experimental structure of Ga(In)As(1) / (Al)GaInP(2) / Ga(In)As(3) / (Al)GaInP(4) in Example 1.

[0028] Figure 2 This is a schematic diagram of the sample preparation process of the present invention. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0030] In the following examples, the blue film model is the SKATTORE ZNG(10) series.

[0031] Example 1

[0032] like Figure 1As shown, the test sample of the multilayer epitaxial structure of the gallium arsenide solar cell to be processed in this embodiment includes a substrate layer and (Al)GaInP(4) layer, Ga(In)As(3) layer, (Al)GaInP(2) layer and Ga(In)As(1) layer deposited sequentially on the substrate from bottom to top. Here, (Al)GaInP(4) layer is GaInP(4) layer, AlInP(4) layer or AlGaInP(4) layer. Similarly, Ga(In)As(3) layer is GaAs(3) layer or GaInAs(3) layer, (Al)GaInP(2) layer is GaInP(2) layer, AlInP(4) layer or AlGaInP(2) layer; and Ga(In)As(1) layer is GaAs(1) layer or GaInAs(1) layer.

[0033] like Figure 2 As shown, a method for preparing a test sample of a gallium arsenide solar cell multilayer epitaxial structure includes the following steps:

[0034] Step 1: For Ge or GaN substrates, no backside protection is required. Use a blue film (acid- and alkali-resistant PVC film) to cover the epitaxial wafer (e.g., ...). Figure 2 The left side of the front surface of the epitaxial wafer (as shown in (1)) is protected by a Ga(In)As(1) layer. If the epitaxial wafer uses a GaAs substrate, the back side also needs to be fully protected. The edges of the blue film covering part should be completely adhered and free of bubbles.

[0035] Step 2: Immerse the sample obtained after Step 1 completely in a solution of hydrogen peroxide and ammonia in a certain ratio (generally, the ratio of hydrogen peroxide to ammonia is 20:1. If the epitaxial layer is thick, the ratio will be adjusted to a maximum of 2:1). After the Ga(In)As(1) layer on the right side is completely etched, take it out and rinse it repeatedly with deionized water. At this time, the exposed surface is the (Al)GaInP(2) layer.

[0036] Step 3: Immerse the cleaned sample completely in concentrated hydrochloric acid (36% to 38% commercially available concentrated hydrochloric acid). After the exposed (Al)GaInP(2) layer is completely corroded, take it out, rinse it repeatedly with deionized water, and then blow it dry with compressed air. At this time, the exposed surface is Ga(In)As(3) layer.

[0037] Step 4: Remove the blue film from the surface. The resulting sample is shown below. Figure 2 As shown in (2), the left side is a Ga(In)As(1) layer and the right side is a Ga(In)As(3) layer;

[0038] Step 5: Use the blue film to protect the upper side of the sample again along the vertical direction of the first film application. The edges of the blue film should be completely adhered without any air bubbles.

[0039] Step 6: Immerse the treated sample completely in a solution of hydrogen peroxide and ammonia in a certain ratio (generally, the ratio of hydrogen peroxide to ammonia is 20:1; if the epitaxial layer is thick, the ratio will be adjusted to a maximum of 2:1). After the exposed Ga(In)As(1) and Ga(In)As(3) layers are completely etched, take it out, rinse it repeatedly with deionized water, and then blow it dry with compressed air. At this time, the exposed surfaces are (Al)GaInP(2) layer and (Al)GaInP(4) layer, respectively.

[0040] Step 7: Remove the blue film on the surface. If there is a protective film on the back, remove it as well. Sample preparation is complete, and the sample obtained is as follows. Figure 2 As shown in (3). The upper left side is a Ga(In)As(1) layer, the upper right side is a Ga(In)As(3) layer, the lower left side is a (Al)GaInP(2) layer, and the lower right side is a (Al)GaInP(4) layer.

[0041] The above sample preparation method is applicable to the alternating growth and testing of arsenide (Ga(In)As) and phosphide ((Al)GaInP) structures. Arsenide (Ga(In)As) is etched with a solution of hydrogen peroxide and ammonia in a certain ratio, and phosphide ((Al)GaInP) is etched with concentrated hydrochloric acid.

[0042] Example 2

[0043] This embodiment is similar to Embodiment 1, except that the test sample of the gallium arsenide solar cell multilayer epitaxial structure to be processed in this embodiment includes a substrate layer and Ga(In)As(4) layer, (Al)GaInP(3) layer, Ga(In)As(2) layer and (Al)GaInP(1) layer deposited on the substrate from bottom to top. The preparation method of this gallium arsenide solar cell multilayer epitaxial structure test sample is different from that in Embodiment 1. The etching solution in step 2 and the etching solution in step 6 are both concentrated hydrochloric acid, and the etching solution in step 3 is a mixed solution of hydrogen peroxide and ammonia.

[0044] The above method for preparing samples is not only energy-saving and time-saving, but also reduces the probability of sample breakage. The test sample simultaneously displays the four interfaces to be tested, allowing for visual assessment of the growth quality of the four epitaxial layers, as well as measurement of technical parameters such as the composition and ion doping concentration of the epitaxial layers, and the thickness and bandgap of each relevant layer.

[0045] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a test sample of a multilayer epitaxial structure of a gallium arsenide solar cell, characterized by, The sample before processing includes a substrate and a fourth epitaxial layer, a third epitaxial layer, a second epitaxial layer, and a first epitaxial layer deposited sequentially on the substrate from bottom to top. The first epitaxial layer is exposed, while the other epitaxial layers are not exposed. The preparation method includes the following steps: Step 1: Protect one side of the sample with the epitaxial layer with a protective film, leaving the other side exposed; Step 2: Immerse the sample treated in Step 1 completely into the first etching solution to etch the exposed first epitaxial layer. After etching is completed, clean and dry it. At this time, the surface of the exposed area in Step 1 is the second epitaxial layer. Step 3: Immerse the sample treated in Step 2 completely in the second etching solution to etch the second epitaxial layer. After etching is completed, clean and dry it. At this time, the exposed surface is the third epitaxial layer. Step 4: Remove the protective film. The resulting sample has a third epitaxial layer on one side and a first epitaxial layer on the other side. Step 5: Protect the side of the sample with the epitaxial layer again with a protective film, so that part of the third epitaxial layer and part of the first epitaxial layer are covered, and part of the third epitaxial layer and part of the first epitaxial layer are exposed; Step 6: Immerse the sample treated in Step 5 completely in the third etching solution. The exposed third epitaxial layer and the first epitaxial layer are etched, exposing the fourth epitaxial layer and the second epitaxial layer respectively. Clean and dry. Step 7: Remove the protective film. At this point, parts of the first to fourth epitaxial layers are exposed. The epitaxial structure is an epitaxial structure in which arsenide layers and phosphide layers are grown alternately. The fourth epitaxial layer, the third epitaxial layer, the second epitaxial layer, and the first epitaxial layer are respectively the fourth phosphide layer, the third arsenide layer, the second phosphide layer, and the first arsenide layer; Alternatively, the fourth epitaxial layer, the third epitaxial layer, the second epitaxial layer, and the first epitaxial layer may be the fourth arsenide layer, the third phosphide layer, the second arsenide layer, and the first phosphide layer, respectively.

2. The method for preparing test samples of gallium arsenide solar cell multilayer epitaxial structure as described in claim 1, characterized in that, The substrate is a Ge substrate, a GaN substrate, or a GaAs substrate. When the substrate is a GaAs substrate, in step 1, a protective film is also needed to completely protect the side of the substrate that does not have an epitaxial layer.

3. The method for preparing test samples of gallium arsenide solar cell multilayer epitaxial structure as described in claim 1, characterized in that, The arsenide layer is a GaAs or GaInAs layer, and the phosphide layer is a GaInP, AlInP, or AlGaInP layer.

4. The method for preparing test samples of gallium arsenide solar cell multilayer epitaxial structure as described in claim 1, characterized in that, The protective film in steps 1 and 5 is an acid- and alkali-resistant PVC film.

5. The method for preparing test samples of gallium arsenide solar cell multilayer epitaxial structure as described in claim 1, characterized in that, When the fourth epitaxial layer, the third epitaxial layer, the second epitaxial layer, and the first epitaxial layer are respectively the fourth phosphide layer, the third arsenide layer, the second phosphide layer, and the first arsenide layer, the first etching solution in step 2 and the third etching solution in step 6 are both mixed solutions of hydrogen peroxide and ammonia, and the second etching solution in step 3 is concentrated hydrochloric acid.

6. The method for preparing test samples of gallium arsenide solar cell multilayer epitaxial structure as described in claim 1, characterized in that, When the fourth epitaxial layer, the third epitaxial layer, the second epitaxial layer, and the first epitaxial layer are respectively the fourth arsenide layer, the third phosphide layer, the second arsenide layer, and the first phosphide layer, the first etching solution in step 2 and the third etching solution in step 6 are both concentrated hydrochloric acid; the second etching solution in step 3 is a mixed solution of hydrogen peroxide and ammonia.

7. The method of claim 1, wherein the method further comprises: In steps 2, 3, and 6, the cleaning and drying processes involve repeated rinsing with deionized water followed by drying with compressed air. ​ 8. The method for preparing test samples of gallium arsenide solar cell multilayer epitaxial structure as described in claim 1, characterized in that, In step 1, the protective film is attached to one half of the sample on the side with the epitaxial layer, while the other half is left exposed.

9. The method for preparing test samples of gallium arsenide solar cell multilayer epitaxial structure as described in claim 8, characterized in that, The protective film is applied to the left half of the area, while the right half is left bare.

10. The method for preparing test samples of gallium arsenide solar cell multilayer epitaxial structure as described in claim 8, characterized in that, In step 6, the protective film is applied to half of the sample on the side with the epitaxial layer.

11. The method of claim 10, wherein the method further comprises: The protective film is applied to the upper half of the area, leaving the lower half exposed, thus covering half of the third epitaxial layer and half of the first epitaxial layer, while exposing half of the third epitaxial layer and half of the first epitaxial layer. ​

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