Deep Defects in MOVPE Grown SiC/AlGaN/GaN Heterostructures

Deep level transient spectroscopy (DLTS) measurement was carried out on GaN/AlGaN/SiC heterostructures prepared by low-pressure metalorganic vapour phase epitaxy. Two kinds of p-type 4H-SiC substrates were employed for the n-GaN layer growth using an n-AlGaN nucleation layer. Two different aluminium concentrations of 30% and 8% were tested. DLTS spectra of on-axis (0001) grown samples exhibit a peak of majority carrier trap with apparent activation energy of 0.78 eV regardless of nucleation layer composition. As the amplitude of this peak is almost insensitive to the height of filling pulses and the space charge region in AlGaN is negligible, the level may be associated with a hole trap in the substrate. The off-axis grown samples show a majority trap-like DLTS peak only under high positive filling pulses. Therefore, activation energy of 0.66 eV obtained for both nucleation layer compositions is related to an interface defect.