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We studied the growth of Si- and Sn-doped homoepitaxial β-Ga2O3 layers on (010)-oriented substrates by metal organic vapor phase epitaxy (MOVPE). At optimal growth conditions (850°C, 5 mbar) the layers were smooth with RMS roughness values of ∼600 pm. A microstructural study by transmission electron microscopy (TEM) revealed a very high crystalline perfection of the layers. No dislocations or planar defects were observed within the field of view of TEM. Using Si as dopant, the free electron concentration could be varied in a range between 1 × 1017 and 8 × 1019 cm−3, while with Sn the doping range was restricted to 4 × 1017−1 × 1019 cm−3. This was explained by a pronounced Sn memory effect in the MOVPE reactor that hampers achieving low carrier densities and by incorporation issues that limit the doping efficiency at high Sn doping levels. The electron mobility for a given doping density increased from ∼50 cm2/Vs for n = 8 × 1019 cm−3 to ∼130 cm2/Vs for n = 1 × 1017 cm−3 independently of the dopant. These values match the best literature data relative to β-Ga2O3 bulk crystals and layers grown by molecular beam epitaxy, setting a new standard for MOVPE-grown layers.
Baldini et al. (Thu,) studied this question.