低温堆積AlN,GaN バッファ層/サファイア基板上に作製したMOCVD n-GaN の深い準位の比較

Abstract

We investigated the variations of trap concentrations in n-GaN films by changing buffer layer type (LT-AlN and GaN) and GaN film thickness. Two electron traps labeled E1 (Ec-0.24eV) and E3 (Ec-0.59eV) are observed in all samples by DLTS spectra. The E1 trap shows the logarithmic capture kinetics, which suggests dislocation-related defects. Trap concentration of this trap is lower in the thick GaN film. In addition, the E1 trap concentration in n-GaN film grown on LT-GaN decrease largely as compared to those on LT-AlN buffer layers. On the other hand, no variation in the E2 trap concentration is observed. This result indicates that the E2 trap corresponds to native point defects. Three hole traps labeled H1 (Ev+0.88eV), H1' (Ev+ ~0.4eV) and H2 (Ev+0.26eV) are found by MCTS spectra. The H1 trap is attributed to the C or VGa. Moreover, this trap is the most dominant and shows no variation in all samples. In case of an additional trap H1', the trap concentration has Gaussian distribution of energy levels. This trap obtained in n-GaN on n+-GaN is lower than n-GaN films on Sapphire substrates.