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Precision synthesis of ultrawide-bandgap semiconductors with a desired crystal phase is of broad interest for developing advanced electronic devices. However, it is highly challenging for gallium oxide (Ga2O3), which is known for versatile crystal phase transition. Here, we report a non-equilibrium epitaxy strategy to confine the crystallization pathways of Ga2O3 toward two distinct metastable polymorphs during the pulsed laser deposition (PLD) growth. This is achieved by synergic control of the substrate orientation and intentional tin (Sn) doping, which dramatically modifies the nucleation and growth kinetics of Ga2O3. Using a-plane sapphires and a medium Sn doping level, we overcome the commonly observed growth limitations of α-phase Ga2O3 (α-Ga2O3) films that are only stable for the initial few monolayers in previous PLD studies. Instead, we stabilize epitaxial α-Ga2O3 films with excellent phase uniformity and crystallinity for a thickness beyond 200 nm. This contrasts to the otherwise formed ε-phase Ga2O3 films by simply switching the sapphire substrate orientation to c-plane regardless of the Sn doping level. Density functional theory calculations reveal the critical role of the surface energy minimization for selective stabilization of metastable phases. This study provides a perspective to improve the non-equilibrium synthesis capability for exploring emerging ultrawide-bandgap semiconductors. [ABSTRACT FROM AUTHOR]

Here we investigate the influence of in situ ozone treatment on structure and carrier transport in La-doped BaSnO3 BLSO) films. It is found that introducing ozone during the film growth significantly inhibits the formation of oxygen vacancies and the occurrence of Sn2+ ions. The amount of oxygen vacancies decreases consistently with the increase of the ozone content, which further increases the in-plane lattice constant along with the relief of the in-plane compressive strain. More importantly, the reduction of oxygen vacancies gives rise to the augment of the threading dislocation density in the BLSO films, leading to the deterioration of carrier mobility. These findings demonstrate that the existence of Sn2+ ions does not apparently suppress the electron mobility in BLSO films, and the presence of oxygen vacancies is beneficial for reducing the density of threading dislocations, facilitating the mobility enhancement. All these findings would be beneficial for understanding the role of oxygen vacancy in carrier transport properties and for further optimizing the mobility of BLSO films. [ABSTRACT FROM AUTHOR]