Growth and Chemical Substitution of Transparent p-Type CuAlO2

Abstract

AbstractCuAlO2 is one of several materials currently being investigated for application as a p-type transparent conducting oxide. In this paper we report a method of making c-axis oriented CuAlO2 thin films which eliminates previously reported phase-purity and surface morphology problems. Thin film precursors of CuA1O2 were deposited on YSZ (100) substrates by roomtemperature radio frequency sputtering. Subsequent annealing in 10mT of oxygen at temperatures as low as 800°C resulted in phase-pure, textured CuAlO2. The films were p-type and transparent with a gap of 3.5eV, but typical carrier concentrations were low (on the order of 1016 cm−3). Oxygen anneals at 700°C in 1 atm of O2 raised this to 1018 cm−3 in some samples. In order to increase the carrier concentration further, we are testing chemical substitution on the metal sublattice. Initial experiments were done with Mg as a dopant, either by direct solid-state synthesis for bulk materials or by alternating deposition of MgO and CuAlO2 during the pulsed laser deposition of thin films. At Mg molar concentrations of 1% or less, the bulk material was phase-pure CuAlO2 by x-ray diffraction, but was mixed-phase CuAl2O4 and CuO when the Mg concentration was increased to 2%. Thin films sputtered from the 1% Mg substituted target crystallized to CuA102 after a 940°C anneal at 10T 02, but were more than 30 times more resistive than the undoped films.