Optical absorption in gallium oxide*

Transparent conducting oxides (TCOs) are a technologically important class of materials used in optoelectronic devices, as TCOs balance two conflicting properties: transparency and conductivity. The requirement of transparency is typically tied to the band gap of the material being sufficiently large to prevent absorption of visible photons. This is a necessary but not sufficient condition: indeed, the high concentration of free carriers, required for conductivity, can also lead to optical absorption. This absorption can occur through direct absorption to higher-lying conduction band states, or by an indirect process, for example mediated by phonons or charged impurities.
We performed a detailed first-principles study of these absorption processes in Ga₂O₃ [1,2], a material with promising applications in high-power devices and UV photodetectors. Our results elucidate the fundamental limitations of optical absorption in Ga₂O₃, which have subsequently been confirmed experimentally [3].

[1] H. Peelaers and C.G. Van de Walle, Appl. Phys. Lett. 111, 182104 (2017).
[2] H. Peelaers and C.G. Van de Walle, Phys. Rev. B 100, 081202 (2019).
[3] A. Singh et al., Appl. Phys. Lett. 117, 072103 (2020).