Individual tuning of ionization potential and electron affinity by composition control of amorphous Cd–In–Ga–O thin film

As ionization potential (I-p) and electron affinity tunable amorphous oxide semiconductors, n-type amorphous Cd-In-Ga-O thin films are fabricated on SiO2 glass substrates by radio-frequency magnetron sputtering method. The I-p and electron affinity of the thin films are determined using ultraviolet photoelectron spectroscopy and ultraviolet-visible-near-infrared spectroscopy. The I-p is tuned from 63 to 7.1 eV by varying Ga concentration from similar to 20 to similar to 50%. In addition, the electron affinity shifts from 3.8 to 4.3 eV by varying Cd concentration. Carrier concentration and mobility strongly depend on Cd concentration for Cd concentrations greater than 50%. Carrier concentration (mobility) decreases (increases) with increasing Cd concentration. In contrast, the influence of Ga concentration seems to be greater for Cd concentrations less than 50%. Carrier concentration varies in the range of 10(17) to 10(20) cm(-33). The maximum value of the mobility is 16 cm(2) V-1 s(-1). (C) 2019 The Ceramic Society of Japan. All rights reserved.