Control of carrier concentration and surface flattening of CuGaO_2 epitaxial films for a p-channel transparent transistor

摘要

A p-type transparent oxide semiconductor, CuGaO_2, was grown epitaxially on (111) single-crystalline yttria-stabilized zirconia (YSZ) substrates by pulsed laser deposition (PLD). Single-phase epitaxial films were obtained in narrow conditions: i.e. 725 ≤ T_s ≤ 780 ℃ at PO_2 = 6 Pa, and 3 Pa ≤ PO_2 ≤ 6 Pa at T_s=750 ℃. The electrical conductivity of the as-deposited films was controlled from 3.3 × 10~(-5) S·cm~(-1) to 1.7 × 10~(-2) S·cm~(-1) by increasing the oxygen partial pressure from 3 to 6.5 Pa. The hole concentration and Hall mobility of the most conductive film were 5 × 10~(17) cm~(-3) and 0.2 cm~2·V~(-1)·s~(-1), respectively. Estimated from the conductivity, the hole concentration was controlled from ～ 10~(14) cm~(-3) to ～ 10~(17) cm~(-3) by the oxygen partial pressure. Post-annealing at 1215 ℃ smoothed the films surface to 0.56 nm in the root-mean-squares roughness and increased the Hall mobility to 0.8 cm~2 V~(-1)·s~(-1), which is the largest value among CuGaO_2 films reported to date.