Optical Properties of In_2xGa_2–2xO₃ Nanowires Revealed by Photoacoustic Spectroscopy

Group III oxides, such as In2O3 and Ga2O3, have proved to be good candidates as active materials for novel electronic devices, including high-mobility transistors, gas sensors, and UV photodetectors. The ability to tune optical and electronic properties is provided by alloying In2xGa2–2xO3 (InGaO) in a broad compositional range. Further development of InGaO compounds in the form of nanowires (NWs) would overcome the technological limitations, such as the substrate crystal lattice mismatch and the inability to fabricate high quality structures above the critical thickness. In this work, optical properties of alloyed InGaO NWs in a wide compositional range are carefully assessed. Unlike classical optical characterization methods, photoacoustic spectroscopy reveals the fundamental absorption edge despite the strong light scattering in porous and randomly oriented nanowires structure. An unusual compositional band gap dependence is also observed, giving insight into the phase segregation effect and increased quality of mixed NWs. In addition, photoacoustic measurements disclose potential applications of InGaO NWs in remote, light-driven loudspeakers because of intense photoacoustic effect in nanowire ensembles in this material system.