Deep level defects in MOCVD-grown <i>β</i>-(Al<i>x</i>Ga1−<i>x</i>)2O3

Abstract

The properties of deep level defects within Si-doped β-(Al0.10Ga0.90)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 EC−0.81 eV, EC−1.6 eV, and EC−4.7 eV, while a weaker level is detected at EC−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-(Al0.10Ga0.90)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(AlxGa1−x)2O3 samples, ranging from x = 3% to 10%. The deep level spectra exhibit consistent sets of four defect states for all β-(AlxGa1−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.