Temperature dependence of the dc conductivity of undoped a-${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$:H alloys: Influence of metastability

The effects of alloying on the shape of the Arrhenius plots of the dc conductivity of glow-discharge a-${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ge}}_{\mathit{x}}$:H with 0≤x≤1 have been investigated in the temperature range 30–250°C. For 0≤x≤0.3 the Arrhenius plots show a downward kink or negative concavity around a temperature ${\mathit{T}}_{\mathit{k}}$, whereas an upward kink or positive concavity is observed for 0.3<x<1. Thermal quenching from 250°C induces a lowering of a nonequilibrium dark dc conductivity in the first case and an increase in the second. Good correlation is found between ${\mathit{T}}_{\mathit{k}}$ and the equilibrium temperature ${\mathit{T}}_{\mathit{E}}$ (in the range 90°C–190°C) and suggests that the shape of the Arrhenius plots is essentially due to metastability. The possible implications to the change in the density-of-states distribution induced by Ge incorporation and by thermal quenching are discussed.