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

We report that
$\hbox{GeO}_{2}$
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
$ \hbox{GeO}_{2}$
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
$\Omega\cdot\hbox{cm}$
) lifetime is 65
$\mu\hbox{s}$
, as determined from the quasi-steady-state photoconductance on Ge wafers with different thicknesses. A 47-nm-thick
$\hbox{GeO}_{2}$
layer can reduce the surface recombination velocity on Ge to 70 cm/s.