Epitaxial κ -(AlxGa1- x)2O3 thin films and heterostructures grown by tin-assisted VCCS-PLD

Abstract

The structural, surface, and optical properties of phase-pure κ-(AlxGa1-x)2O3 thin films on c-sapphire and STO(111):Nb substrates as well as on MgO(111) and κ-Ga2O3 templates are reported as a function of alloy composition for x < 0.4. The thin films were grown by tin-assisted pulsed laser deposition (PLD). For the variation of the Al-content, we utilized radially segmented PLD targets that enable the deposition of a thin film material library by discrete composition screening. Growth on κ-Ga2O3 (001) thin film templates enhanced the phase pure growth window remarkably up to x = 0.65. The crystallization of the κ-phase was verified by X-ray diffraction 2θ-ω-scans for all samples. Both in- and out-of-plane lattice constants in dependence on the Al-content follow a linear relationship according to Vegard's law over the complete composition range. Atomic force microscope measurements confirm smooth surfaces (Rq ≈ 1.4 nm) for all investigated Al-contents. Furthermore, bandgap tuning from 4.9 eV to 5.8 eV is demonstrated and a linear increase in the bandgap with increasing Al-content was observed.