Temperature dependence of electron mobility in Bi12GeO20 and Bi12SiO20 using the time-of-flight technique

Abstract

We have measured the temperature dependence of the electron mobility between ∼200 and 300 K in undoped and 0.3% Fe-doped Bi12GeO20 (BGO) and undoped Bi12SiO20 (BSO) using a time-of-flight technique. We found that mobilities calculated from the observed transit times were independent of sample thickness and applied voltage, but depended approximately exponentially on temperature. The hole current transients were very weak and featureless, and consequently we were unable to measure mobilities for holes. The measured drift mobilities varied from 6.1×10−4 to 0.10 cm2/Vs for undoped BGO, 6.1×10−4 to 0.0170 cm2/Vs for 0.3% Fe-doped BGO, and ∼5×10−4 to 0.014 cm2/Vs for undoped BSO. Values of the microscopic mobility were estimated to be 5.9, 2.3, and 1.4 cm2/Vs for undoped, 0.3% Fe-doped BGO, and undoped BSO, respectively. From the temperature dependence of the electron mobility we obtained an activation energy for the dominant trap of Et=0.31 eV for undoped BGO, Et=0.34 eV for 0.3% Fe-doped BGO, and Et=0.31 eV in the undoped BSO sample. These values are interpreted as the trap depth of the main traps dominating the mobility and agree well with values obtained from the analysis of thermally stimulated conductivity measurements performed previously.