Novel oxide amorphous semiconductors: Transparent conducting amorphous oxides

A working hypothesis to find wide gap oxide semiconductors was proposed on the basis of simple considerations. The hypothesis predicts that amorphous double oxides composed of heavy metal cations (HMCs) with an electronic configuration (n - 1)d(10)s(0) are promising candidates for a novel class of amorphous semiconductors. Electrical and optical properties of three amorphous double oxides composed of the HMCs, a-AgSbO3, Cd2GeO4 and Cd2PbO4, were examined, following this hypothesis. It was found that when carrier electrons are generated via the formation of oxygen vacancies or doping of excess cations by ion implantation, these three wide band gap amorphous oxides show high electrical conductivities of 10(-1) to 10(2) S cm(-1) at similar to 300 K and the conductivity remains almost constant down to 77 or 4 K for high carrier concentrations (> 10(18) cm(-3)). This high conductivity originates primarily from a large Hall mobility of similar to 10 cm(2) V-1 s(-1), which is higher by several orders of magnitude than that in amorphous transition metal oxides, Si:H and chalcogenides. A variety of chemical compositions for a novel oxide amorphous semiconductor are suggested.