Effects of Ga concentration, process conditions, and substrate materials on properties of ZnMgBeGaO ultraviolet-range transparent conducting films

• Electrical properties of ZnMgBeO films are improved by the Ga doping.
• Crystal quality of the films degraded with increasing growth temperature (Tg).
• Resistivity of the films drastically increased with the O2 addition.
• Band gap of the films decreased with the Tg increase and the O2 addition.
• The film composition changed with the Tg increase and the O2 addtion.

The effects of gallium (Ga) concentration, growth variables and substrate materials on the optical, electrical, and structural properties of the sputter grown Zn0.92-xMg0.05Be0.03GaxO films were studied in detail. The resistivity significantly decreased by doping the film with Ga, from 46.8 Ω cm to 1.6 × 10− 3 Ω cm, indicating that Ga is an effective donor. It was observed that the crystalline quality of the films degrades, the resistivity increases with increasing growth temperature (Tg), and the resistivity drastically increased with the addition of oxygen gas to the Ar plasma. It was proposed that the Tg effect is mainly due to the increase in the Ga concentration and the oxygen effect is due to the decrease in the point defect density and the passivation of Ga donors. It was also observed that the band gap of the films decreases with increasing Tg and O2 concentration, due to the combined effects of the Burstein–Moss effect and the compositional changes. Films grown on GaN substrates showed significantly improved crystalline quality compared with those of samples grown on Si or SiO2, due to the reduced lattice mismatch.