Metal Organic Chemical Vapor Deposition 2: Heteroepitaxial MOCVD Growth of $$\upalpha $$-, $$\upbeta $$-, and $$\upvarepsilon $$-Ga$$_2$$O$$_3$$ Thin Films on Sapphire Substrates

This chapter reviews the heteroepitaxial growth of \(\upalpha \)- , \(\upbeta \)- , and \(\upvarepsilon \)-gallium oxide (Ga\(_2\)O\(_3\)) films, with a focus on those grown using the metalorganic chemical vapor deposition (MOCVD) technique. Variations in growth conditions and substrates result in the growth of different polymorphs of Ga\(_2\)O\(_3\) or combinations of them. \(\upbeta \)-Ga\(_2\)O\(_3\) is consistently reported as the dominant phase to grow at high substrate temperatures >700 \(^{\circ }\)C. At lower substrate temperatures, \(\upalpha \)- and \(\upvarepsilon \)- metastable phases have been observed. Other growth conditions and substrates that have yielded \(\upalpha \)- and \(\upvarepsilon \)-Ga\(_2\)O\(_3\) epitaxial films are also discussed. Doping of MOCVD-grown \(\upbeta \)-Ga\(_2\)O\(_3\) is also briefly reviewed, where Si and Sn are the most commonly used dopants. Doping concentrations between \(1\times 10^{17}\) and \(8\times 10^{19}\) cm\(^{-3}\) have been achieved, with corresponding electron mobility values between \(\sim \)130 and 50 cm\(^2\)/Vs.