Comparison of triethylgallium and diethylgallium ethoxide for β-Ga₂O₃ growth by metalorganic vapor phase epitaxy

The suitability of diethylgallium ethoxide (Et₂GaOEt) containing Ga–O bonds as a Ga precursor for beta-gallium oxide (β-Ga₂O₃) growth by metalorganic vapor phase epitaxy (MOVPE) was investigated. Because estimating the growth behavior by thermodynamic analysis is difficult as a result of a lack of knowledge about the thermodynamics of Et₂GaOEt, the growth behavior was estimated by observing its pyrolysis and combustion processes. Mass spectrometric analysis of gases sampled directly from an MOVPE reactor when only Et₂GaOEt was supplied revealed that Et₂GaOEt was decomposed to gallane, ethylene, and acetaldehyde by β-hydrogen (β-H) elimination at temperatures greater than 450 °C. However, when Et₂GaOEt was supplied together with O₂ to the MOVPE reactor maintained at 1000 °C, the combustion of hydrogen and carbon derived from Et₂GaOEt was accelerated as the O₂ supply was increased. In addition, the amount of O₂ required for the complete combustion of Et₂GaOEt (i.e., the amount required for the growth of β-Ga₂O₃) was clarified. On the basis of this pyrolysis/combustion behavior, homoepitaxial growth of β-Ga₂O₃ layers on β-Ga₂O₃ substrates was investigated at 1000 °C using Et₂GaOEt as a Ga precursor and the growth behavior was compared with that when triethylgallium (Et₃Ga) was used as a Ga precursor. Because both Ga precursors ultimately provide Ga gas after β-H elimination, no substantial difference in the growth rate was observed with respect to the amount of Ga atoms injected into the growth reactor. In addition, no substantial difference in crystallinity was observed; homoepitaxial layers grown at 0.7—0.8 μm/h were single crystals without twins, whereas those at 1.5—1.6 μm/h had twins. Et₂GaOEt was found to be suitable as a Ga precursor for MOVPE of β-Ga₂O₃, with performance comparable to that of Et₃Ga.