Conversion of an ultra-wide bandgap amorphous oxide insulator to a semiconductor

Abstract

The variety of semiconductor materials has been extended in various directions, for example, to very wide bandgap materials such as oxide semiconductors as well as to amorphous semiconductors. Crystalline β-Ga2O3 is known as a transparent conducting oxide with an ultra-wide bandgap of ~4.9 eV, but amorphous (a-) Ga2Ox is just an electrical insulator because the combination of an ultra-wide bandgap and an amorphous structure has serious difficulties in attaining electronic conduction. This paper reports semiconducting a-Ga2Ox thin films deposited on glass at room temperature and their applications to thin-film transistors and Schottky diodes, accomplished by suppressing the formation of charge compensation defects. The film density is the most important parameter, and the film density is increased by enhancing the film growth rate by an order of magnitude. Additionally, as opposed to the cases of conventional oxide semiconductors, an appropriately high oxygen partial pressure must be chosen for a-Ga2Ox to reduce electron traps. These considerations produce semiconducting a-Ga2Ox thin films with an electron Hall mobility of ~8 cm2V−1 s−1, a carrier density Ne of ~2 × 1014 cm−3 and an ultra-wide bandgap of ~4.12 eV. An a-Ga2Ox thin-film transistor exhibited reasonable performance such as a saturation mobility of ~1.5 cm2 V−1 s−1 and an on/off ratio >107.