Tunable Ultra-Wide Bandgap Semiconductor Alloys

We present research on the optical properties of (In_xGa_1-x)₂O₃ nanocrystal films at compositions 0 ≤ x ≤ 1. The films were synthesized using gallium and indium nitrate precursors on Si and quartz substrates. These alloys have potential applications in technologies such as oxide-based transistors, memory cells, and tunable light emitter materials.

The optical gap of In₂O₃ is about 3 eV, that of Ga₂O₃ is 5 eV, by alloying with the desired percentage of the two end-members, alloys with optical gaps between 3 eV to 5 eV can be achieved. The issue is that the crystal structure of beta-Ga₂O₃ is monoclinic and that of In₂O₃ is cubic bixbyite, thus solubility across the entire composition range is not possible. The results from the transmission experiments indicate that the nanocrystal alloys are single phase, and soluble up to at least x=0.46 of indium composition. This result is consistent with the previous theory. The optical gap was found to span continuously from 4.86 eV for the beta-Ga₂O₃ film down to 3.78 eV for the film with x=0.46 indium composition. For higher indium composition x=0.7, the optical gap of the alloy was found to be high; about 4.14 eV instead of following the decreasing trend with indium composition. This implies that the alloy is saturated, it is Ga-rich, and is in the phase separation range. Moreover, a small signal from the optical gap of In-rich ~ 3 eV appeared in the spectrum confirming that in this sample two crystal structures co-exist.