Investigation of electrically active defects in GaN using deep-level transient spectroscopy

In this thesis I will present and discuss the results of electrical and deep-level transient spectroscopy (DLTS) measurements on GaN semiconductors. I report on the effect of sputter metal deposition on the type and concentration of defects in the Si-doped GaN. By comparing the results of the sputtered sample with the evaporated sample, I show a significant increase in leakage current and carrier concentration in the sputter-deposited diode. The DLTS results show that defects detected in the sputtered sample are dissimilar to the defect in the evaporated sample, and defect concentration in the sputtered sample is much higher. I also show that defect concentration in the sputtered sample has dropped 10 times from the surface to 10 nm deeper into the sample, which strongly proved the defect is sputter-induced. These results suggest that additional defects caused by sputter deposition can result in a significant degradation in GaN device performance. I report on the sidewall damages created during reactive-ion etching (RIE) in silicondoped GaN mesa diodes. The defects in mesa diodes of different shapes and areas are characterised using DLTS, and their densities are compared. I show that the concentration of defects is higher in mesa diode with larger area and square shape, due to additional defects are introduced through the sidewall during RIE. The defect distribution in mesa diodes is described by a model, which has precisely reflected the shape and area dependence of defect concentration. I report on the effect of iron doping on the conductivity and deep levels of n-type GaN. The results of electrical measurements show that the leakage current and carrier concentration in the Fe/Si co-doped sample is lower than those in the Si-doped sample. DLTS spectrum of the co-doped sample suggests that Fe doping contributes to the formation of FeGa - VN complex while compensates native vacancies and vacancy complexes, which are major sources of free carriers. The semi-insulating nature of Fe doped GaN and the slow response of Fe concentration in Fe doping are also discussed.