Hydrogen passivation of interstitial Zn defects in hetero-epitaxial InP cell structures and influence on device characteristics

Abstract

Hydrogen passivation of hetero-epitaxial InP solar cells is of interest for deactivation of dislocations and other defects caused by the cell/substrate lattice mismatch that currently limits the photovoltaic performance of these devices. Here we show that in addition to passivation of dislocations, hydrogen deactivates interstitial Zn donor defects present within the Zn-doped emitter of metal organic chemical vapor deposition (MOCVD)-grown p+n hetero-epitaxial InP devices. Zn interstitial passivation increases the forward bias turn-on voltage of hetero-epitaxial InP diodes by as much as 280 mV over the non-hydrogenated value, reaching a value of 960 mV which is close to that obtained for homo-epitaxial diodes. The increase is reproducible and is not observed for either n+p structures or homo-epitaxial p+n structures. Through a combination of photoluminescence, C–V profiling, SIMS and I–V measurements we explain that the source of the voltage enhancement is a combination of decreased acceptor compensation in the emitter and decreased current losses due to depletion region recombination and shunting paths associated with the high concentration of Zn interstitials in Zn-doped hetero-epitaxial InP. © 1997 John Wiley & Sons, Ltd.