Strain Relaxation via Phase Transformation in High-Mobility SrSnO₃Films

SrSnO3 (SSO) is an emerging ultrawide band gap (UWBG) semiconductor with potential in high-power applications. In-plane compressive strain was recently shown to stabilize the high-temperature tetragonal phase of SSO at room temperature (RT), which exists at T ≥ 1062 K in bulk. Here, we report on the study of strain relaxation in the epitaxial, tetragonal phase of Nd-doped SSO films grown on GdScO3 (110) (GSO) substrates and how it influences the electronic transport properties. The thinnest SSO film (thickness, t = 12 nm) yielded a fully coherent tetragonal phase at RT. At 12 nm < t < 110 nm, the tetragonal phase first transformed into the orthorhombic phase, and then at t ≥ 110 nm, the orthorhombic phase began to relax by forming misfit dislocations. Remarkably, the tetragonal phase remained fully coherent until it completely transformed into the orthorhombic phase. A significant increase in mobility from 14 to 73 cm2 V-1 s-1 was discovered between 12 and 330 nm. Using thickness- and temperature-dependent electronic transport measurements, we discuss the important roles of the surface, phase coexistence, and misfit dislocations on carrier density and mobility in Nd-doped SSO. This study provides unprecedented insight into the effect of thickness and strain relaxation behavior and their consequences for electronic transport in doped SSO with implications for high-power electronic devices.