Bandgap engineering and Schottky barrier modulation of ultra-wide bandgap Si-doped β-(AlxGa1−x)2O3 single crystals

Abstract

In order to balance the contradiction between on and off performances of the Schottky diodes, Si-doped β-(Al_xGa_1−x)₂O₃ (β-AlGaO) single crystals were designed based on the bandgap and impurity engineering of β-Ga₂O₃. The bandgap became larger with Al element doping. The photoluminescence properties of Si-doped β-AlGaO were measured and the emission band was separated into three Gaussian peaks with wavelengths of 372 nm, 410 nm, and 453 nm. These peaks were derived from a self-trapped hole (STH), (V_Ga + V_O)¹⁻, and V_Ga²⁻, respectively. This demonstrated that Al only acted on valence and conduction bands, without introducing intermediate transition levels, indicating excellent bandgap regulation. The thermal properties of Si-doped β-AlGaO were demonstrated for the first time. Noticeably, a carrier concentration of 4.61 × 10¹⁸ cm⁻³ and a resistivity of 0.099 Ω cm were observed at room temperature in Si-doped β-AlGaO. At low temperatures, the dominant mechanism was ionized impurity scattering, while at high temperatures, optical phonon scattering became dominant. The on-resistance of Schottky barrier diodes (SBDs) prepared using this material was only 1.57 mΩ cm², and the Schottky barrier was as high as 1.21 eV. At similar Schottky barrier heights, the on-resistance was 10 times lower compared to β-Ga₂O₃ based SBDs. In addition, the device has a high forward current density (J_@2V) of 521 A cm⁻² at a forward voltage of 2.0 V and an ON-/OFF-current ratio of up to 10⁹. This work presents a viable approach for fabricating high-performance vertical structure devices using Si-doped β-AlGaO materials based on the bandgap structure and impurity engineering.