'University of Pretoria - Department of Philosophy'
Abstract
In this study, we investigated defects introduced in n-GaAs with different carrier densities by electron irradiation and sputter deposition by means of conventional deep level transient spectroscopy (DLTS) as well as high resolution Laplace deep-level transient spectroscopy (LDLTS). In electron-irradiated material, we found that the well-known E3 defect, of which the origin has long been under discussion, consisted of three components (E3a, E3b and E3c). By constructing Arrhenius plots and performing annealing studies, and by comparing our results with literature, we could deduce that the E3a, the main component of the E3 is related to the VAs, while the E3b is related to the Asi and the E3c was related to the VGa-SiGa. In addition, the E3c was metastable and had a concentration that increased linearly with doping concentration. Further electrical characterization included I-V and C-V measurements, as well as measurements of the introduction rate, metastability, electric field emission mechanisms and capture cross-sections. For the sputter-deposited Schottky contacts, DLTS depth profiles showed that the defects were confined close to the surface and that their depth range depended strongly on the doping concentration, and corresponded roughly with the depletion depth of the Schottky diodes. We conclude that the diffusion of these defects was stronlgy enhanced by the conditions (free carrier density and electric field) in the depletion region. Six defects (S1, S2, S3, S4, S5 and S6) were observed by conventional DLTS and were further investigated by L-DLTS. One of these defects, the S6, could be split into two components while three of them (S1, S3 and S5) were metastable. The transformation kinetics of the metastable defects were investigated and we conclude that the prefactor of S5 to S3 transformation was related to free carrier emission but for the S3 to S5 transformation is larger than would be expected. The activation energy of these transformations was similar to that required for arsenic vacancy (VAs) diffusion. The real capture cross sections as well as capture barriers were measured for the S3, S4 and S5 defects.Thesis (PhD)--University of Pretoria, 2019.PhysicsPhDUnrestricte
