Effect of oxygen on the optoelectronic properties of amorphous hydrogenated silicon

Abstract

Experimental observations of the effect of a small percentage (1.6 - 5.7 at.%) of deliberately incorporated oxygen on various properties of sputtered $a$-Si:H reveal a broadening of the absorption edge, an increase in the density of states near the Fermi level (determined from capacitance and conductance measurements), an increase in the photoelectron mobility-lifetime product ${(\ensuremath{\mu}\ensuremath{\tau})}_{n}$, a decrease in the photohole ${(\ensuremath{\mu}\ensuremath{\tau})}_{p}$ product, and a widening of the photoluminescence peak. These are accompanied by the appearance of a Si-O vibrational mode in the infrared spectra at about 1000 ${\mathrm{cm}}^{\ensuremath{-}1}$. We also report apparently the first observation of photoluminescence in sputtered $a\ensuremath{-}\mathrm{S}\mathrm{i}$:$\mathrm{O}$ (${C}_{o}=55$ at.%). The above results are self-consistently interpreted in terms of a suggested modification of the gap density of states in $a\ensuremath{-}\mathrm{S}\mathrm{i}$. It is confirmed that the incorporation of oxygen at the 1 at.% level into $a\ensuremath{-}\mathrm{S}\mathrm{i}$:$\mathrm{H}$ is detrimental to the photovoltaic performance of the material.