Fe-related optical transitions in floating zone and Czochralski grown beta-Ga2O3 crystals

Gallium oxide (Ga2O3), a promising candidate for high-power electronics, may be doped with Fe to control the native n-type conductivity and produce semi-insulating single-crystalline substrates. Here, intentionally as well as unintentionally Fe-doped beta-Ga2O3 crystals grown by the Czochralski (Cz) and the floating zone (FZ) methods are studied. While the Cz samples contain Ir on the order of 1017 cm(-3) due to the Ir crucible, the FZ samples are free of this contaminant. Photoinduced electron paramagnetic resonance (EPR) is performed by illuminating the samples with light emitting diodes from 0.7 to 4.7 eV while monitoring the intensity of the EPR signal. The following optical transitions associated with Fe are observed: one between 1 and 2 eV occurs in both Cz and FZ samples, another near 2.5 eV is unique to Cz Ga2O3, and a third near 3 eV appears in FZ material. The transition below 2 eV is the well-studied Fe2+-to-Fe3+ transition, intrinsic to Fe. Near 2.5 and 3 eV, the amount of Fe3+ decreases by capturing electrons excited from other defects present near or below the middle of the bandgap. By comparing Cz and Ir-free FZ crystals, we show that the 2.5 eV transition is primarily caused by Ir in Fe-doped Cz samples, whereas the similar to 3 eV transition observed in FZ samples could be caused by isolated or complex intrinsic defects. By differentiating transitions between Cz and FZ material, the results will be relevant to epitaxial films, which do not contain the Ir present in the commonly studied Cz material.