Optical and Electronic Transport Properties of Electrodeposited Thallium(III) Oxide Films

Thallium oxide is a degenerate n-type semiconductor which can be electrodeposited from aqueous solution at room temperature. Thin films were characterized by transmission and specular reflectance spectroscopy and by four-point resistivity and Hall measurements. Optical parameters were determined by fitting the observed specular reflectance to the Drude equation. Due to the high free carrier concentration, the material reflects strongly in the near-infrared, and the band-to-band optical transitions are shifted by up to 1.1 eV by the Moss-Burstein effect. The optical and electrical properties of the films were a function of the deposition overpotential. Films grown at 44 mV had an intrinsic bandgap of 0.66 eV, resistivity of 2.8 x 10{sup -4} ohm-cm, mobility of 27 cm{sup 2}Vs, and conduction band effective mass of 0.43m{sub o}. Films grown at 300 mV had an intrinsic band gap of 0.51 eV, resistivity of 7.8 x 10{sup -5} ohm cm, mobility of 93 cm{sup 2}V s, and conduction band effective mass of 0.29m{sub o}. Mobilities measured by contact and optical methods are similar, which shows the optical technique may be used for conditions in which contact methods might fail. 20 refs., 11 figs., 2 tabs.