Cathodoluminescence of undoped and Si-doped ε-Ga2O3 films

Cathodoluminescence (CL) investigations are performed on nominally undoped and Si-doped epsilon-Ga2O3 samples grown by metal-organic vapor phase epitaxy on (0001)-Al2O3 substrates, using different carrier gases. All films exhibit a broad low-temperature CL emission extending over the photon energy range 2-3.4 eV. Emission deconvolution suggests that four narrower bands centered at about 2.4, 2.75, 3.0 and 3.15 eV may well account for the broad band. While the position of these peaks results independent of the growth conditions, significant intensity differences are observed. A general reduction of the broad emission is evidenced as the Si concentration increases. No band-to-band recombination is observed. Temperature dependence of the CL signal shows a trend consistent with radiative transitions from the CB to deep acceptor states, probably of intrinsic nature.