【International Papers】Deep level defects in MOCVD-grown β-(AlₓGa₁₋ₓ)₂O₃

      Researchers from the Ohio State University have published a dissertation titled " Deep level defects in MOCVD-grown β-(Al_xGa_1−x)₂O₃" in Journal of Applied Physics.

Background

      Beta-phase gallium oxide (β-Ga₂O₃) has emerged as a promising ultra-wide bandgap (UWBG) semiconductor for high-voltage and RF electronic devices due to its large bandgap (~4.8 eV), high breakdown field, and availability of large-area melt-grown substrates. Various device structures, including MESFETs and MOSFETs, have demonstrated excellent performance with high breakdown voltages and large drain currents. More recently, β-(Al₁₋ₓGaₓ)₂O₃/Ga₂O₃ heterojunction-based MODFETs have attracted attention, offering two-dimensional electron gas (2DEG) channels with high mobility and sheet charge density. However, trap states within the barrier and interface can significantly degrade device performance by increasing leakage, reducing ON/OFF ratios, and introducing noise. While prior studies have focused on structural properties and alloy behavior of β-(Al₁₋ₓGaₓ)₂O₃, little to no information exists at present regarding the presence and properties of deep level defects that act as traps in epitaxial  β-(AlₓGa₁₋ₓ)₂O₃ ⁠. This work provides a systematic exploration of trap states within a range of compositions from 3% to 10% Al content and uses prior results on 0% Al (i.e., β-Ga₂O₃) as a control comparison.

Abstract

      The properties of deep level defects within Si-doped β-(Al_0.10Ga_0.90)₂O₃ epitaxial layers grown by metalorganic chemical vapor deposition (MOCVD) were characterized by deep level optical spectroscopy and deep level transient (thermal) spectroscopy. Three dominant defect states are E_C−0.81 eV, E_C−1.6 eV, and E_C−4.7 eV, while a weaker level is detected at E_C−0.37 eV. Lighted C–V measurements show a consistent trend between trap concentrations increasing with the Al content and measured net doping, suggesting that these deep levels are responsible for significant carrier compensation from the Si donors. Comparisons with prior work on MOCVD-grown β-Ga₂O₃ layers revealed that total trap concentrations in the β-(Al_0.10Ga_0.90)₂O₃ alloy can be as much as 10–100 times larger than those of β-Ga₂O₃ for samples grown in the same MOCVD system. The role of Al alloying in the formation of defects was further explored by studying a separate set of β- (Al_xGa_1−x)₂O₃ samples, ranging from x = 3% to 10%. The deep level spectra exhibit consistent sets of four defect states for all β-(Al_xGa_1−x)₂O₃ samples. Comparison of deep level spectra between compositions shows a monotonic increase in trap activation energies and trap concentrations as the Al content, and bandgap, increases. Considering the variation of bandgap and conduction band offset energies, the trend among individual traps implies that these states may follow or partly follow a vacuum-referred binding energy model, useful in predicting the trap positions at higher Al-content alloys of interest for modulation-doped field effect transistors and ultraviolet photodetectors.