GaAs solar cells grown on GaP

This paper describes investigations of GaAs solar cells grown on (100) GaP by MOCVD. This work is being carried out as part of an effort to fabricate GaAs and other III-V cells from film structures grown on silicon substrates coated with a pseudomorphic GaP film. Heteroepitaxial growth of GaAs on GaP is interesting regardless of the potential application to GaP-coated Si. Problems associated with the removal of SiO² from Si substrates, and possible regrowth of SiO² prior to growth of GaAs, and difficulties caused by a large mismatch in thermal expansion coefficients do not exist when growing GaAs on GaP. The lattice mismatch between GaAs and GaP is 3.57%, similar to that between Si and GaAs (3.93%). Thus, one knows that dislocations in the heteroepitaxial GaAs film structures grown on GaP are primarily a result of lattice mismatch. After growing a P/N cell structure, arrays of 0.109 cm² cells are fabricated on the heteroepitaxial film structure with the use of photolithography. To date, the best cell performance has been an active area efficiency of 10.2%, with an active area J_SC=18.1 mA/cm², FF=0.745 and V_OC=757 mV