Great reduction of the hole effective mass in wide bandgap semiconductors by highly mismatched alloying

Abstract

Many wide bandgap semiconductors suffer from a large hole effective mass, and inherent defects severely limit their performance. LiGaSe₂, as a direct wide bandgap selenide semiconductor, also faces such challenges. In this work, we present a strategy for valence band engineering of LiGaSe₂ through high mismatch O-alloying. Hybrid functional calculations show that LiGa(Se_1−xO_x)₂ alloys can greatly reduce their hole effective mass, drastically improving the hole mobility. Specifically, at x = 6.25%, the hole effective mass of the alloy along the Γ−Y direction is only 0.295m₀, indicating an approximate 80% reduction compared to LiGaSe₂. This physically counterintuitive reduction can be attributed to the introduction of a small amount of O-2p orbitals into the valence band, which strongly overlaps with Ga-3d orbitals, forming strong p–d hybridization. Furthermore, the band anticrossing interaction between the O-2p orbitals and the original orbitals pulls down the conduction band, reducing the band gap of the LiGa(Se_0.9375O_0.0625)₂ alloy to 3.037 eV, which is sufficient to maintain excellent visible light transparency. These findings highlight the potential of semiconductor LiGa(Se_1−xO_x)₂ alloys as transparent conducting materials and offer a novel solution for other similar wide bandgap semiconductors.