Inducing conductivity in polycrystalline ZnO1-x thin films through space charge doping

Abstract

We induce ultra-high carrier charge density in polycrystalline zinc oxide thin films on glass with a thickness of few tens of nm, achieving carrier concentrations as high as 2.2×1014 cm−2, well beyond the Ioffe-Regel limit for an insulator-metal transition in two dimensions. The sheet resistance is consequently lowered by up to 5 orders of magnitude to about 2 k Ω/◻ without alteration of transparency thanks to our space charge doping technique. Electrostatic doping of such a large band-gap semiconductor is quite challenging, and a high surface potential is required in order to induce conductivity at the interface. Through magneto-transport measurements performed at low temperature on the doped films, we show that both weak localization and weak anti-localization of charge carriers can be observed and that these quantum interference phenomena can be modulated by the carrier concentration and temperature.

Deep vs shallow nature of oxygen vacancies and consequentn-type carrier concentrations in transparent conducting oxides

“…Some experiments [81,82] have shown a variation in conductivity and mobility with P O 2 more indicative of the presence of interstitials or cation vacancies (which have also been shown to be present using positron annihilation spectroscopy) [83][84][85][86][87], but oxygen vacancies have been proposed to explain the intrinsic n-type conductivity [36,78,88] and persistent photoconductivity [37,76], as well as other experimental results [89][90][91][92]. Similar to SnO 2 , computational studies tend to indicate that the oxygen vacancy is deep, with the (2+/0) transition occurring at about 1 eV below the CBM [46][47][48][49][50][51][52][53].…”