Electron mobility in crystalline and amorphous metal-oxide semiconductors

Charge carrier mobility in amorphous semiconductors is significantly reduced when compared to the crystalline phase. For instance, room-temperature electron mobility in crystalline silicon is 1400 cm²/V.s, while that for amorphous silicon is only ~0.1 cm²/V.s. Amorphous metal-oxide semiconductors are unique in this respect, as they display relatively high electron mobilities when compared to their crystalline counterpart. Here we investigate the microscopic origin of this intriguing effect. Using first-principles molecular dynamics to generate amorphous configurations and electronic structure calculations of prototype metal oxides, we investigate why metal-oxide semiconductors display relatively high electron mobilities even in an amorphous phase. We analyze their band structure, the effects of volume, the change in the absolute band edge positions, and provide a detailed comparison between amorphous silicon and Ga₂O₃, paying special attention to the presence of band tail states and the change in band gaps.