Full-momentum exciton landscape and macroscopic quantum phase diagram in two-dimensional gallium oxides

Abstract

High-temperature exciton macroscopic quantum phases have a wide application prospect in many fields such as ultrahigh power photonics and quantum information, and are extremely difficult to realize due to the strong thermal dissociation effect. In this study, the exciton dispersions and macroscopic quantum phase diagrams of two-dimensional (2D) ultrawide bandgap semiconductors I–Ga2O3 and II-Ga2O3 are investigated for the first time. Both I–Ga2O3 and II-Ga2O3 possess the complex excitonic composition and morphology, resulting from their highly degenerate and flat valence bands. For the exciton B1 (B1') with an ultra-large binding energy of 1.14 (1.03) eV in I–Ga2O3, the phase transition temperature from free exciton to Bose-Einstein condensation (TBEC) is as high as 356 (679) K, respectively. The critical carrier densities for the formation of electron-hole liquid at room temperature (NEHL) are 1.3 × 1013 cm−2 and 1.8 × 1013 cm−2, respectively. For the free exciton B1 with an ultra-large binding energy of 1.49 eV in II-Ga2O3, TBEC reaches 365 K and NEHL is 5.9 × 1013 cm−2. Our findings extend the material basis for the research of exciton macroscopic quantum phases and will boost their applications in novel optoelectronic devices.