Anisotropy of hydrogen plasma effects in bulk n-type beta-Ga2O3

Abstract

Bulk n-type beta -Ga2O3 samples with orientation (-201) and (010) were exposed to a high density hydrogen plasma at 330 degrees C for 0.5h. The effects were radically different for the two orientations. For the (-201) sample, H plasma exposure increased the net surface concentration of shallow donors from 2.7x10(17)cm(-3) to 2.6x10(18)cm(-3), with the shallow donors having an ionization energy close to 20meV as deduced from the temperature dependence of the series resistance of Ni Schottky diodes. By sharp contrast, H plasma exposure of the (010) sample led to a strong decrease in the net shallow donor density from 3.2x10(17)cm(-3) to below 10(15)cm(-3) in the top 0.9 mu m of the sample and to 3.2x10(16)cm(-3) near the edge of the space charge region at 0V, with the total width of the region affected by plasma treatment being close to 1.1 mu m. For both orientations, we observed a major decrease in the concentration of the dominant E2 traps near E-c-0.82eV related to Fe acceptors. The deep trap spectra in hydrogenated samples were dominated by the E2* traps commonly ascribed to native defects in beta -Ga2O3. The peak of these traps with a level near E-c-0.74eV was masked in the starting samples by the peak of the E2 Fe acceptors present in high concentration, so that E2* only broadened the Fe peak on the low temperature side, but could be revealed by the modeling of the spectra. The concentration of the E2* center was not strongly affected in the hydrogen-treated samples with orientation (010), but in the (-201) samples, the concentration of the E2* peak was greatly enhanced. The results are discussed in conjunction with previous reports on hydrogen plasma treatment of beta -Ga2O3 and on obtaining p-type conductivity in the surface layers of beta -Ga2O3 crystals annealed in molecular hydrogen at high temperatures [Islam et al., Sci. Rep. 10, 6134 (2020)].