Sn-Induced Phase Stabilization and Enhanced Thermal Stability of κ-Ga2O3 Grown by Mist Chemical Vapor Deposition

Tin (Sn)-doped orthorhombic gallium oxide (kappa-Ga2O3) films were grown on (0001) sapphire by mist chemical vapor deposition. It is known that kappa-Ga2O3 is more stable than alpha-Ga2O3 (corundum) but less stable than beta-Ga2O3 (monoclinic). This thermodynamic stability means an optimal growth temperature (T-g) of the kappa-phase (600-650 degrees C) is also in between the two. At first, it was observed that Sn doping induced the kappa-phase during the growth of the beta-phase (T-g = 700 degrees C). Interestingly, Sn could also promote the beta-phase even under the growth condition that strongly favors the alpha-phase (T-g = 450 degrees C). The postgrowth annealing tests at 800-1000 degrees C showed that the thermal stability of the kappa-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 kappa to beta after annealing at 800, 900, and 1000 degrees C for 30 min each. This enhancement of thermal stability promises more reliable high-power and high-frequency devices for which kappa-Ga2O3 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.

Automated summary

By doping with Sn, the thermal stability of gallium oxide films can be enhanced, especially in the growth of kappa-Ga2O3. Increasing Sn concentration can suppress radiative recombination, although it is not correlated with crystal quality.