Abstract
This thesis is concerned with the study of deep energy levels in ion implanted gallium arsenide (GaAs) using deep level transient spectroscopy (D.L.T.S.). The D.L.T.S. technique is used to characterise deep levels in terms of their activation energies and capture cross-sections and to determine their concentration profiles. The main objective is to characterise the effects on deep levels, of ion implantation and the related annealing processes. In the majority of cases assessment is carried out using Schottky barrier diodes, these being appropriate to the study of majority carrier traps. Low doses of selenium ions 1 to 3x1012 cm-2 are implanted into vapour phase epitaxial (V.P.E.) GaAs and the effects of post-implantation thermal and pulsed laser, annealing are compared. In the former case there is no significant change in the total trap concentration as a result of the complete process of implantation, silicon nitride encapsulation, and thermal annealing at 900°C. In contrast, pulse laser annealing at an energy density of 0.5 J.cm-2 using a Q-switched ruby laser, introduces high concentrations of traps within the region of melting. The process of oxygen implantation with doses in the range 1x1012 to 5x1013 cm-2 followed by thermal annealing at about 750°C, introduces a deep level at 0.79eV from the conduction band. Oxygen implantation, at doses of 5x1013 cm-2, into V.P.E. GaAs produces a significant increase in the concentration of the A-centre (0.83eV). The measured total trap concentrations however, do not account for the compensation of the free carriers. High doses of zinc (1015cm-2) are implanted into n-type V.P.E. GaAs to form shallow p-type layers. The resulting p+-n diodes are used to study minority carrier traps using a forward bias injection pulse. The D.L.T.S. system described in the text is used to measure levels in the range 0.16 to 1.1eV (for GaAs) with a sensitivity of the order 1:103. Modifications to this system, based on the 'Miller' correlator, result in improvements in both the sensitivity and resolution.