The mobility of photo-induced carriers in disordered As₂Te₃ and As₃₀Te₄₈Si₁₂Ge₁₀

Abstract

The paper presents measurements of the drift mobility of charge carriers in radio-frequency sputtered films of As₂Te₃ and As₃₀Te₄₈Si₁₂Ge₁₀, as determined from the initial rate of rise of the transient photoconductivity. The data indicate that the carriers, which are concluded from subsidiary experiments to be holes, exhibit trap-limited band transport in the room-temperature region, interacting with localized levels which in both materials are situated about 0·22 eV from the Fermi level. At low temperatures, a transition occurs to a process of hopping between centres in a second set of localized states about 0·13 eV from the Fermi level, these centres again being present in both As₂Te₃ and As₃₀Te₄₈Si₁₂Ge₁₀. It is concluded that the greater compositional disorder of the latter material results in a change of position of the valence band mobility edge, but does not appreciably modify the localized state distribution within the mobility gap.