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

Abstract

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 6.5 to 7.1 eV by varying Ga concentration from ∼20 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 10¹⁷ to 10²⁰ cm⁻³. The maximum value of the mobility is 16 cm² V⁻¹ s⁻¹.