Optical and electrical properties of sputter-deposited ZnMgAlO UV-range transparent conducting films

Abstract

Effects of the Al concentration and the growth variables on the optical and electrical properties of UV-range Zn 0.88-x Mg 0.12 Al x O TCO films were studied in detail. As the Al content increased from 0% to 5%, the band gap increased from 3.6 to 3.8 eV, with the optical transmittance maintained at ∼90% within the 370-800 nm wavelength range. The resistivity significantly decreased by doping the film with Al, to 2-3 × 10 −3 cm, but was not critically affected by the addition of a larger amount of Al. The resistivity drastically increased with the addition of O 2 gas into the Ar sputter plasma and/or by increasing growth temperature. It was proposed that the density of the point defects, as well as the presence of the dopant impurity, plays a key role in determining the carrier concentration. Minimum resistivity, ∼3 × 10 −3 cm, was obtained when grown at 10 mTorr pressure, 125 W RF power, Ar ambient and room temperature.

Effects of Ga concentration, process conditions, and substrate materials on properties of ZnMgBeGaO ultraviolet-range transparent conducting films

“…It was also proposed that hydrogen interstitials and substitutional hydrogens could act as a shallow donor in ZnO, providing major amount of free electrons [17]. It is believed that films with better stoichiometry and lower hydrogen concentration are grown and the number of the defects within the crystal decreases [18], when oxygen-rich plasmas are employed, leading to a substantial decrease in the electron concentration. The Hall mobility then increases with increasing oxygen pressure, as the scattering of electrons by the defects decreases [18].…”

“…It is believed that films with better stoichiometry and lower hydrogen concentration are grown and the number of the defects within the crystal decreases [18], when oxygen-rich plasmas are employed, leading to a substantial decrease in the electron concentration. The Hall mobility then increases with increasing oxygen pressure, as the scattering of electrons by the defects decreases [18]. It is also suspected that the passivation of Ga donors must be also occurring at the same time, considering the large amount of the free electrons that were reduced by the growth in oxygen with plasma.…”