Temperature Dependence of $\beta-Ga_2O_3$ Heteroepitaxy on c-plane Sapphire using Low Pressure Chemical Vapor Deposition.

$\beta-Ga_2O_3$ has drawn significant attention for power electronics and deep ultraviolet (UV) photodetectors owing to its wide bandgap of ~ 4.4 - 4.9 eV and high electric breakdown strength ~7-8 MV/cm. Growth of $\beta-Ga_2O_3$ epitaxial thin films with high growth rate has been recently reported using low pressure chemical vapor deposition (LPCVD) technique. In this work, we have investigated the effect of growth temperature on $\beta-Ga_2O_3$ films grown on c-plane sapphire substrates using LPCVD. We performed growths by varying temperatures from 800$^{\deg}$C to 950$^{\deg}$C while keeping all other growth parameters (Ar/O$_2$ gas flow rates, growth pressure, and Gallium precursor to substrate distance) constant. Optical, structural, and surface characterizations are performed to determine the bandgap, phase purity, crystal orientation, and crystalline quality of the grown thin films. Amorphous islands of $Ga_2O_3$ are observed at growth temperature of 800$^{\deg}$C while continuous and crystalline (-201) oriented $\beta-Ga_2O_3$ thin films are achieved for growth temperatures of 850$^{\deg}$C to 950$^{\deg}$C. Crystallinity of the films is found to improve with increase in growth temperature with a minimum rocking full width at half maximum of 1.52$^{\deg}$ in sample grown at 925$^{\deg}$C. For all the samples grown at and above 875$^{\deg}$C, transmittance measurements revealed an optical bandgap of ~4.77-4.80 eV with high growth rate of ~6 ${\mu}$m/hr.