Formation Mechanism of Cu-based Ohmic Contacts for GaAs Solar Cells

Copper contacts on GaAs are gaining increasing attention for low-cost high-efficiency solar cell devices. Cu/Ge/Pd and Cu/Pt/Ti/Pt contacts have been reported to achieve low specific contact resistivities in the range of 10-5 Ω cm2. A preliminary study for the formation mechanism of these two Cu-based structures on both n-type and p-type GaAs substrates subjected to different thermal annealing conditions is reported. The results indicate that the formation of the Cu
₃
Ge and PdGaxAsy compounds in conjunction with the creation of Ga vacancies are among the reasons for low contact resistance for n-GaAs. The high work function of Pt and high melting temperature of both Pt and Ti help to reduce the contact resistance for p-GaAs.