$\hbox {GeO}_{2}$ Passivation for Low Surface Recombination Velocity on Ge Surface

We report that GeO₂ passivation reduces surface recombination on Ge through both the reduction of interface state density and the field effect of the oxide charge. Furthermore, the photoluminescence intensity increases with increasing GeO₂ thickness, mainly because of the reduction in interface state density since the fixed charge density remains almost constant. The direct-to-indirect band-gap emission ratio also remains unchanged after passivation. The p-Ge (1-3 Ω·cm) lifetime is 65 μs, as determined from the quasi-steady-state photoconductance on Ge wafers with different thicknesses. A 47-nm-thick GeO₂ layer can reduce the surface recombination velocity on Ge to 70 cm/s.