Anomalous mass renormalization in two-dimensional electron systems on ultra-wide bandgap semiconductor $\beta$-Ga${}_2$O${}_3$

Abstract

Two-dimensional electron systems (2DESs) at wide-bandgap semiconductor surfaces and interfaces are fertile ground for emergent quantum phenomena. Here, we use micro-focused angle-resolved photoemission spectroscopy (ARPES) to resolve the momentum-space electronic structure of a surface 2DES in $\beta$-Ga${}_2$O${}_3$, an ultra-wide bandgap semiconductor with a band gap of 4.7 eV. In situ electron doping of cleaved, high-purity $\beta$-Ga${}_2$O${}_3$ single crystals produces an essentially circular Fermi surface. With the self-consistent Poisson-Schrödinger model, the 2D electrons are estimated to be confined within approximately 1.2 nm beneath the surface, with an internal electric field of approximately 18 MV cm${}^{-1}$. Our analysis based on ARPES measurements reveals nearly a twofold increase in the electron mass at high sheet carrier densities. This trend deviates from the conventional behavior reported for wide-bandgap semiconductors and indicates mass renormalization beyond the conventional screening-based picture. Our results provide quantitative momentum-space benchmarks for the Fermi-surface geometry and density-dependent quasiparticle dispersion of the $\beta$-Ga${}_2$O${}_3$ 2DES, opening a route to studying density-tunable interfacial quantum states in the UWBG regime.

arXiv comment24-page main manuscript, 3 main figures; Supplementary Information appended (13 supplementary figures and 1 supplementary table). Revised title, author list, abstract, and analysis