In the making process of multi-layer thin-film solar cells, in order to reduce the consumption of semiconductor materials, the substrate, on which the single-crystal layers are grown by MOCVD technology, needs to be peeled off from the grown layers.
ZnSe/GaAs/Ge is a hopeful group of single-crystal thin-film composite semiconductor materials matching the solar spectrum. It can be applied to various solar cells, such as photoelectrochemical (PEC) solar cells, photovoltaic (PV) solar cells and Schottky solar cells.
Here, the three-function-layer single-crystal thin-film Sckottky solar cell is taken as an instance to discuss the technique of peeling off substrates. The structure and doped situation of the composite semiconductor materials is shown in Fig.1.
The following are steps of making the solar cell and peeling off the substrate:

1. Taking an n-GaAs single crystal pallet as a substrate. Its crystal orientation is [100] deviated to [111] 8~9 degrees;
2. Growing a Ga^0.3Al^0.7As layer on the substrate by MOCVD technique as the layer for being peeled off. Its thickness is 6 µm;
3. Then growing an n⁺ -GaAs layer also by MOCVD technique, doped from 10¹⁸cm^-3 to 10¹⁷ cm³. The thickness is 2 µm;
4. Moreover, growing an n-Ge layer by MOCVD technique, doped from 10¹⁷ cm³ to 10¹⁶ cm³. Its thickness is 2 µm;
5. After that, deposit a metal (such as Ag) electrode on the surface of the Ge layer and then being adhered to a glass plate shown as Fig.2;
6. Protecting the Ge layer and glass plate with wax and etching off the Ga^0.3Al^0.7 As layer in HF acid so that the grown layers are separated from the substrate, as shown in Fig.3. HF acid only etches the Ga^0.3Al^0.7 As layer but not the GaAs layer;
7. Peeling off the wax and clean the surface of the GaAs layer, then growing an n⁺⁺ -ZnSe layer doped from 10¹⁸ cm³ to 10¹⁹ cm³ by MOCVD technique, on the GaAs layer. The thickness is 2 µm;
8. Depositing an Au layer with 600 thickness on the surface of the ZnSe layer. This will result in forming a Schottky junction between ZnSe and Au;
9. Setting up grill electrode on the surface of the Au layer;
10. Finally, depositing a reflection reducing coating. Now a three-function-layer single-crystal thin-film Schottky solar cells has been made, as shown in Fig.4.

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emails: ghli@sjzri.edu.cn or gcli@hebust.edu.cn

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Last updated March 29, 1999

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