Sn-Induced Phase Stabilization and Enhanced Thermal Stability of κ-GaO Grown by Mist Chemical Vapor Deposition.

Tin (Sn)-doped orthorhombic gallium oxide (κ-GaO) films were grown on (0001) sapphire by mist chemical vapor deposition. It is known that κ-GaO is more stable than α-GaO (corundum) but less stable than β-GaO (monoclinic). This thermodynamic stability means an optimal growth temperature ( ) of the κ-phase (600-650 °C) is also in between the two. At first, it was observed that Sn doping induced the κ-phase during the growth of the β-phase ( = 700 °C). Interestingly, Sn could also promote the κ-phase even under the growth condition that strongly favors the α-phase ( = 450 °C). The postgrowth annealing tests at 800-1000 °C showed that the thermal stability of the κ-phase depends on the Sn concentration. The higher the Sn concentration, the more stable the phase. The one with the highest Sn content showed no phase transition from κ to β after annealing at 800, 900, and 1000 °C for 30 min each. This enhancement of thermal stability promises more reliable high-power and high-frequency devices for which κ-GaO is suitable. Although there was no correlation between Sn-induced phase stabilization and the crystal quality, cathodoluminescence revealed that increasing Sn concentration led to the strong suppression of the radiative recombination at 340 nm from the vacancy-related donor-acceptor pairs. This observation suggests that the phase stabilization by Sn could be related to a specific Ga site Sn replaces in the orthorhombic structure.