THE STUDY OF MECHANICAL DEFORMATION RESISTANCE OF Α-GA<sub>2</sub>O<sub>3 </sub>EPITAXIAL LAYERS USING THE NANOINDENTATION TECHNIQUE
Gallium oxide (Ga<sub>2</sub>O<sub>3</sub>) is a wide-band semiconducting material with an energy gap width E<sub>g</sub>=4.8-5.0 eV, high conductivity (λ~10.9-27.0 W/(m·K)), and radiation and chemical resistance. Its energy gap width and conductivity allow in the future using the material in the structures of power equipment and optoelectronic devices to increase their energy performance, i.e. to decrease heating and increase productive capacity. Radiation resistance, high breakdown field, and optical asymmetry of Ga<sub>2</sub>O<sub>3</sub> make it attractive for application when designing UV-photoelectric receivers and space systems. The electrical and optical properties of Ga<sub>2</sub>O<sub>3</sub> are amply studied, but there are no systematic data on its physical and mechanical properties (hardness, Young’s modulus, and crack resistance). The paper investigated the deformation in α-Ga<sub>2</sub>O<sub>3</sub> epitaxial layers during nanoindentation. For indentation, the authors used NanoTest (Micro Materials Ltd.) hardness meter. The surface (0001) of α-Ga<sub>2</sub>O<sub>3</sub> crystalline layers produced in the process of chloride gas epitaxy on sapphire (Al<sub>2</sub>O<sub>3</sub>) substrates with basic (0001) orientation was investigated. For the first time, the authors experimentally obtained the values of α-Ga<sub>2</sub>O<sub>3</sub> hardness and Young’s modulus using the Oliver-Farr method. The dependences of the indentation load on the penetration depth demonstrated the deviation from linearity, including stress relaxation coming from the pop-in phenomenon. The average values of nanohardness H and Young’s modulus E were 17 and 281 GPa, respectively. The obtained H and E values demonstrate higher characteristics compared to the formerly studied β-Ga<sub>2</sub>O<sub>3</sub> epitaxial layers. This discrepancy can be explained by the more close-packed arrangement of the α-Ga<sub>2</sub>O<sub>3</sub> structure (the corundum type) than one of monoclinic β-Ga<sub>2</sub>O<sub>3</sub>. The study shows that α-Ga<sub>2</sub>O<sub>3</sub> leaves the majority of semiconducting materials behind in its mechanical properties conceding only to gallium nitride (GaN) and sapphire (Al<sub>2</sub>O<sub>3</sub>).