The electrically active defects introduced in GaAs by electron beam deposition (EB) of Ta were characterised. The effect of electron beam deposition on the electrical properties of GaAs was evaluated by current-voltage (I-V), capacitance¬voltage (C- V) and deep level transient spectroscopy (DL TS). However, when electronic devices are formed by EB, defects may be introduced into the semiconductor material, depending on the properties of the metal being deposited. Depending on the application, these defects may have either advantages or detrimental effects on the performance of such a device. I-V measurements indicated that the EB induced damage results in an increase in ideality factor and decrease in the barrier height with increasing the applied substrate bias, while C- V measurements showed that EB deposition also caused a decrease in the barrier height. DL TS studies on the same material in the temperature range of 20 - 350 K showed that at least three electrically active defects are introduced during EB deposition, with energies (0.102 ± 0.004, 0.322 ± 0.014 and 0.637 ± 0.029 eV) within the band gap. DL TS data was used to construct concentration profiles of these defects as a function of depth below the surface. It was found that the defect concentration increases with increasing substrate bias during the deposition, irrespective of the direction of the applied bias. This may be related to the I-V characteristics of the SBDs. The SBDs investigated by IV measurements showed that GaAs yields SBDs with poorer characteristic. The influence of EB deposition on the device properties of SBDs fabricated on GaAs is presented. These device properties were monitored using a variable temperature I-V and C- V apparatus. In order to have an understanding of the change in electrical properties of these contacts after EB deposition, it is necessary to characterise the EB induced defects. DL TS was used to characterise the defects in terms of their D L TS signature and defect concentration.
Dissertation (MSc (Physics))--University of Pretoria, 2006.