Strain Relaxation via Phase Transformation in High-Mobility SrSnO₃ Films

Abstract

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.

Deep-UV Transparent Conducting Oxide La-Doped SrSnO3 with a High Figure of Merit

“…Since the bulk lattice parameters of the Pnma phase are 4.035 and 4.033 Å along the a – and c + directions, respectively, the initial growth of a – a – c + alignment with larger lattice parameters being the in-plane axes can be stabilized with the imposed tensile strain. It should be noted that while recent studies have reported strain-driven phase transition of SrSnO 3 to the tetragonal I 4/ mcm phase with an octahedral rotation pattern of a 0 a 0 c – , , XRD result from the films studied here shows significantly smaller (∼3%) out-of-plane lattice parameters compared to those of the tetragonal phase and, therefore, excludes the possibility of tetragonal phase formation.…”

“…This is in contrast to the previously reported situation, where the compressive strain on GdScO 3 (110) substrates is relaxed as the SLSO film becomes thicker. 44 , 45 Figure 4 c illustrates the rocking curves for 105 nm 4% SLSO, 33 nm SrHfO 3 , 55 nm BaHfO 3 and the MgO (001) substrate. The MgO (001) single-crystal substrate has a sharp peak shape with full width at half-maximum (FWHM) of around 0.032.…”

“…La-doped BaSnO 3 single crystals and epitaxial films are shown to have an outstanding electron mobility of 320 and 150 cm 2 V –1 s –1 , respectively. , SrSnO 3 possesses a wider band gap ( E g ∼ 4.6 eV) and smaller effective mass ( m e ∼ 0.23 m 0 ) than BaSnO 3 ( E g ∼ 3.1 eV, m e ∼ 0.42 m 0 ). , In bulk powders, an orthorhombic phase ( Pnma ) is known to be the stable phase at room temperature with lattice constants of a ortho = 5.703 Å, b ortho = 5.709 Å, and c ortho = 8.065 Å (its pseudocubic lattice constant a pc = 4.034 Å) . Trivalent ions such as La 3+ , Ta 3+ , Nd 3+ , and Sm 3+ were used as effective n-type dopants − by substituting for the Sr site without affecting the band structure . Additionally, pentavalent ions such as Nb 5+ , Sb 5+ , and Pb 5+ in place of Sn were studied as n-type dopants. − It is worth noting that the La dopant creates shallow donor levels in SrSnO 3 , which indicates that extra electrons in La ions are easily activated .…”

Hysteretic Magnetoresistance in a Non-Magnetic SrSnO3 Film via Thermal Coupling to Dynamic Substrate Behavior

“…The room-temperature Hall-effect measurements yielded a carrier concentration of 1.9 × 10 19 cm –3 in this sample. Figure (a) shows an insulating-like behavior, i.e., an increasing sheet resistance with decreasing temperature, which we attribute to the disorder at the surface . A sharp rise in R s was observed at T < 6 K. To investigate the low-temperature transport mechanism, we performed Zabrodski analysis (see inset of Figure (a)), yielding a slope of 0.6.…”

“…Figure 2(a) shows an insulating-like behavior, i.e., an increasing sheet resistance with decreasing temperature, which we attribute to the disorder at the surface. 32 A sharp rise in R s was observed at T < 6 K. To investigate the low-temperature transport mechanism, we performed Zabrodski analysis (see inset of Figure 2(a)), yielding a slope of 0.6. This result reveals that the low-temperature (T < 6 K) insulating behavior is associated with the Efros−Shklovskii (ES) variable range hopping.…”