Deep defects in GaN/AlGaN/SiC heterostructures

Deep level transient spectroscopy (DLTS) measurements were carried out on GaN/AlGaN/SiC heterostructures prepared by low-pressure metalorganic vapor phase epitaxy. Si-doped n-GaN layers were grown using an n-AlGaN nucleation layer (8% and 30% of aluminum) on two kinds of p-type 4H-SiC substrates. The DLTS spectra of on-axis (0001) grown samples exhibit a dominant peak of a majority carrier trap with apparent activation energy close to 0.80 eV and capture cross section of about 5×10−14 cm2 regardless of the AlGaN composition. The energy of this deep level decreases with increasing electrical field due to Poole–Frenkel effect. Carrier capture kinetics indicates interacting point defects arranged along a line, probably a threading dislocation. Two additional traps (0.52 and 0.83 eV) were found in on-axis samples with 8% AlGaN composition. For 30% Al content, only a 0.83 eV level was detected. Majority carrier trap with activation energy of 0.66 eV was observed in the off-axis grown samples. This level is probably related to an interface defect or to a defect lying near the heterojunction interface.