Crystal orientation dependence of deep level spectra in proton irradiated bulk beta-Ga2O3

Abstract

The effects of 20MeV proton irradiation with fluences of 5x10(14) and 10(15)p/cm(2) on electrical properties of lightly Sn doped n-type (net donor concentration 3x10(17)cm(-3)) bulk beta-Ga2O3 samples with (010) and (-201) orientation were studied. Proton irradiation decreases the net donor density with a removal rate close to 200cm(-1) for both orientations and similar to the electron removal rates in lightly Si doped beta-Ga2O3 epilayers. The main deep electron traps introduced in the beta-Ga2O3 crystals of both orientations are near E-c-0.45eV, while in Si doped films, the dominant centers were the so-called E2* (E-c-0.75eV) and E3 (E-c-0.1eV) traps. Deep acceptor spectra in our bulk -Ga2O3(Sn) crystals were dominated by the well-known centers with an optical ionization energy of near 2.3eV, often attributed to split Ga vacancies. These deep acceptors are present in a higher concentration and are introduced by protons at a higher rate for the (010) orientation. Another important difference between the two orientations is the introduction in the surface region (similar to 0.1 mu m from the surface) of the (010) of a very high density of deep acceptors with a level near E-c-0.27eV, not observed in high densities in the (-201) orientation or in Si doped epitaxial layers. The presence of these traps gives rise to a very pronounced hysteresis in the low temperature forward current-voltage characteristics of the (010) samples. These results are yet another indication of a significant impact of the orientation of the beta-Ga2O3 crystals on their properties, in this case, after proton irradiation. Published under an exclusive license by AIP Publishing.