Optical absorption of Fe in doped Ga2O3

This study investigates the Fe impurities believed to act as deep acceptors that contribute to electrical compensation of the n-type conductivity in as-grown Ga2O3. A variation of the traditional optical absorption measurement, photoinduced electron paramagnetic resonance (EPR) spectroscopy, is used to identify charge transitions in bulk Fe-doped and Mg-doped Ga2O3 with the support of hybrid functional calculations. Steady-state photo-EPR measurements show that the first optically induced change in Fe3+ occurs at 1.2 eV, significantly larger than the calculated defect levels for Fe. However, the optical cross section spectrum determined from time-dependent photo-EPR measurements compare well with a calculated cross section spectrum for the Fe2+-to-Fe3+ transition when the relaxation energy predicted from the density functional theory is folded into the model. This work explicitly demonstrates the need for an accurate accounting of electron-lattice coupling when interpreting optically induced phenomena.