Material quality and dislocation trapping in hydrogen passivated heteroepitaxial InP/GaAs and InP/Ge solar cells

Plasma hydrogenation has recently been demonstrated to be highly effective in passivating dislocations in heteroepitaxial InP and is a promising technique for achieving viable heteroepitaxial InP solar cells. In this paper, the effects of hydrogen on the fundamental properties of three dislocation related hole traps in heteroepitaxial InP/GaAs are presented. Hydrogen passivation significantly alters the dislocation trapping kinetics, causing point defect-like behavior consistent with a transformation from dislocation-related defect bands within the InP bandgap to a low concentration of individual deep levels after hydrogenation. Furthermore, hydrogen passivation is shown to shift the dominant space charge generation center from E_c-0.71 eV to E_c-0.92 eV, away from midgap. A model is proposed which explains these effects on the basis of decreased electronic interaction between dislocation sites. Finally, a comparison of InP material quality grown on GaAs, Ge and GaAs/Ge substrates is presented, and hydrogen passivation of InP/GaAs/Ge structures is reported