High mobility yttrium doped cadmium oxide thin films

Donor doped CdO thin films on c-plane sapphire are prepared by reactive co-sputtering from Cd-metal and Y-metal targets which are driven using pulsed-dc and RF power respectively. Intrinsic CdO exhibits a carrier density of 1.8 x 10(19) cm(-3) and a mobility of 330 cm(2) V-1 s(-1). By increasing the Y-flux, carrier density values can be increased smoothly and reproducibly to a maximum value of 3.3 x 1020 cm(-3). Mobility increases with Y flux, and exhibits a broad plateau between approximately 5 x 10(19) cm(-3) and 2 x 10(20) cm(-3). Higher carrier concentrations produce a sharp drop in mobility. The increase in mobility is attributed to a reduction of intrinsic donors (i.e., oxygen vacancies) with increasing carrier density while the ultimate decrease in mobility results from a combination of factors including cadmium vacancies, reduced crystal quality, and smaller crystallite sizes, all of which accompany carrier density values greater than the mid 10(20) cm(-3) range. This work demonstrates that CdO thin films can be prepared by magnetron sputtering with transport properties and crystal quality that are comparable to those grown using molecular beam epitaxy. (C) 2017 Author(s).