Role of barrier and buffer layer defect states in AlGaN/GaN HEMT structures

We have used low energy electron-excited nanoscale luminescence spectroscop y (LEEN) to detect the defects in each layer of AlGaN/GaN HEMT device struc tures to correlate their effect on two-dimensional electron gas (2DEG) conf inement. Also, we have used Auger electron spectroscopy (AES) to detect the chemical composition as a function of lateral position on a growth wafer a nd to correlate chemical effects with electronic properties. We investigate d several high-quality AlGaN/GaN heterostructures of varying electrical pro perties using incident electron beam energies of 0.5-15 keV to probe electr onic state transitions within each of the heterostructure layers. The LEEN depth profiles reveal differences between successful and failed structures and highlight the importance of acceptor deep defect levels in the near 2DE G region. Variations in the GaN and AlGaN band edge emissions, as well as t he yellow defect emission across an AlGaN/GaN heterostructure growth wafer have been observed. AES and LEEN spectroscopy of the growth wafer suggest t hat variation in the cation concentration may play a role in the mechanism responsible for the deep acceptor level emission in the AlGaN barrier layer .