Influence of plasma process on III-V/Ge multijunction solar cell via etching

Abstract

In this paper, the impact of the plasma process for III-V/Ge heterostructure etching on both the morphology and the photovoltaic performance is investigated for the fabrication of multijunction solar cells with a through cell via contact architecture. Three different plasma chemistries (BCl3/Cl2, SiCl4/Cl2, and SiCl4/H2/Cl2) have been studied in order to obtain anisotropic etching through the multijunction heterostructure without inducing photovoltaic performance loss. SiCl4-based plasma chemistries have been found more suitable to achieve deep via hole etching (∼ 30 µm) without lateral etching. The study suggests that SiClx passivation is more efficient to protect the sidewalls compared to BClx. The addition of H2 in SiCl4/Cl2 mixture appears to reinforce the sidewall passivation and thus to limit the lateral etching. III-V/Ge triple junction solar cells with standard grid line and busbar front and back contact have been fabricated on which shallow via-holes have been etched in order to assess the associated photovoltaic performance loss to each plasma etching process. Despite the fact that similar hole sidewall profiles are obtained, the electrical performances are plasma chemistry dependant. This study demonstrates that the SiCl4/H2/Cl2 process presents the lowest losses with almost no induced open-circuit voltage degradation, which makes it promising for the through cell via contact architecture recently proposed for concentrated photovoltaics (CPV) solar cells.