Gap state distribution of hydrogenated amorphous silicon-germanium alloys

Abstract

The gap state distribution (GSD) of aSi 1−xGe x:H alloys in the upper half of the mobility gap has been studied as a function of Ge content by using transient photoconductivity, steady state photoconductivity, and space charge limited conduction in n +in + structures. The gap state density is found to increase as the Ge-content in the alloy increases. The general shape of GSD, however, remains similar to that in aSi:H for Ge-content up to about 30%, with the deep states distributed in energy with a characteristic temperature, T 0, of around 1000 K and the shallow states characterized by T 0 < 500 K. For Ge content higher than 40%, a hump appears in GSD at around 1.2 eV above the valence band mobility edge. The possible origin of the new states is discussed.