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

Abstract

Many wide bandgap semiconductors suffer from large hole effective mass, the inherent defect severely limits their performance. The LiGaSe2, as a direct wide bandgap oxide semiconductor, also faces such challenges. In this work, we present a strategy for valence band engineering of LiGaSe2 by high mismatch O-alloying. Hybrid functional calculations show that semiconductor LiGa(Se1-xOx)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 0.295 m0¬, indicating an approximate 80% reduction compared to LiGaSe2. This physically counterintuitive reduction can be attributed to introducing a small amount of the 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(Se0.9375O0.0625)2 alloy to 3.037 eV, which is sufficient to maintain excellent visible light transparency. These findings highlight the potential of the semiconductor LiGa(Se1-xOx)2 alloys as transparent conducting materials and offer a novel solution for other similar wide bandgap semiconductors.