Control of carrier concentration and surface flattening of CuGaO2 epitaxial films for a p-channel transparent transistor

A p-type transparent oxide semiconductor, CuGaO2, 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 ≤ Ts ≤ 780 °C at PO2 = 6 Pa, and 3 Pa ≤ PO2 ≤ 6 Pa at Ts = 750 °C. 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 × 1017 cm− 3 and 0.2 cm2∙V− 1∙s− 1, respectively. Estimated from the conductivity, the hole concentration was controlled from ∼ 1014 cm− 3 to ∼ 1017 cm− 3 by the oxygen partial pressure. Post-annealing at 1215 °C smoothed the films surface to 0.56 nm in the root-mean-squares roughness and increased the Hall mobility to 0.8 cm2 V− 1∙s− 1, which is the largest value among CuGaO2 films reported to date.