Low Subthreshold Slope AlGaN/GaN MOS-HEMT with Spike-Annealed HfO2 Gate Dielectric.

AlGaN/GaN metal-oxide semiconductor high electron mobility transistors (MOS-HEMTs) with undoped ferroelectric HfO2 have been investigated. Annealing is often a critical step for improving the quality of as-deposited amorphous gate oxides. Thermal treatment of HfO2 gate dielectric, however, is known to degrade the oxide/nitride interface due to the formation of Ga-containing oxide. In this work, the undoped HfO2 gate dielectric was spike-annealed at 600 °C after the film was deposited by atomic layer deposition to improve the ferroelectricity without degrading the interface. As a result, the subthreshold slope of AlGaN/GaN MOS-HEMTs close to 60 mV/dec and on/off ratio>109 were achieved. These results suggest optimizing the HfO2/nitride interface can be a critical step towards a low-loss high-power switching device.

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

Tin (Sn)-doped orthorhombic gallium oxide (κ-Ga2O3) films were grown on (0001) sapphire by mist chemical vapor deposition. It is known that κ-Ga2O3 is more stable than α-Ga2O3 (corundum) but less stable than ß-Ga2O3 (monoclinic). This thermodynamic stability means an optimal growth temperature (T g) 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 ß-phase (T g = 700 °C). Interestingly, Sn could also promote the κ-phase even under the growth condition that strongly favors the α-phase (T g = 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 ß 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-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.