High-lifetime GaAs on Si using GeSi buffers and its potential for space photovoltaics

Record-high minority carrier lifetimes exceeding 10 ns are reported for GaAs grown on Si wafers using compositionallygraded GeSi buffers coupled with monolayer-scale control of the GaAs/Ge interface nucleation during molecular beam epitaxy. The GaAs layers are free of anti-phase domain disorder, with threading dislocation densities at or below 2×106 cm−2. Secondary ion mass spectroscopy (SIMS) reveals that crossdiffusion of Ga, As and Ge at the GaAs/Ge interface formed on the graded buffers are below detection limits in the interface region. Test diodes yielded excellent I–V characteristics, matching those of GaAs diodes on Ge and GaAs wafers, indicating that to a first order, threading dislocations do not limit device performance.