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.