Via-hole etching process for back-contact InGaP/GaAs double heterojunction solar cells

Abstract

High tech industry such as the unmanned aerial vehicles and drones develops, GaAs thin film solar cells that can be attached to streamlined form is studied. Backside contact technology is employed to improve efficiency of the InGaP/GaAs double heterojunction solar cell by making both the anode and cathode electrodes on the backside of the solar cells. It offers the advantages of easy module interconnect, homogeneous surface look, and the higher efficiency. To apply it to the double or triple-junction tandem solar cells, via-hole etching and through via metallization processes are required. A three-step etching process of via-hole for the inverted InGaP/GaAs double heterojunction back-contact solar cells has been developed. Back-contact solar cells are the way to increase the efficiency of the solar cells by eliminating the shading effect caused by the front electrode. In this paper, the etching of via-hole in the InGaP/GaAs double heterostructure has been developed using the three-step etching process based on a combination of two-step dry etching and wet etching realize back-contact solar cell. The via-holes with 3.2 µm depth were fabricated by process combined with dry and wet etching. Two different plasma chemistries such BCl3/Cl2 and CH4/H2 were involved using Inductively Coupled Plasma reactive ion etching (ICP-RIE) and reactive ion etching (RIE), respectively. The pressure and gas ratio were changed to form Sa smooth and tapered sidewall of the via-hole. The remaining layers were removed through wet etching with HCl/H3PO4/H2O2 solution by varying temperatures from 20 ℃ to 40 ℃. After the dielectric insulating layer (SiNx) was deposited on the sidewall of the via-hole. The 3.47-thick Au film was filled in the via-hole to reach the front side n-contact layer. To transfer back-contact solar cell from GaAs substrate to flexible substrate, the ELO process and GaAs wet etching process were studied. The difference between ELO process with stress and ELO process without stress was compared, and GaAs wet etching conditions were optimized.