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This thesis examines the kinetics of carrier capture and emission from dislocations in silicon (Si) and gallium nitride (GaN) using deep level transient spectroscopy (DLTS) and Laplace DLTS (LDLTS).Laplace DLTS is a powerful tool in characterising point defect related emission, but until now it has not been used extensively for investigating emission from extended defects. Using LDLTS, broad DLTS peaks arising from dislocations in Si containing oxidation-induced stacking faults (OISF) were resolved into multiple emission rates. For the first time, the change in emission rates from deep levels due to the band edge modification at dislocations was evidenced by LDLTS.Silicon can be grown virtually defect free, but dislocations may be introduced in very-large scale integration (VLSI) to act as impurity gettering centres. Additionally, the interstitial oxygen inherent in Czochralski (Cz) silicon can be made to segregate to dislocation cores by specific bending and annealing conditions to increase the mechanical hardness of wafers. This process is termed dislocation locking. In this work, Cz-Si with different amounts of oxygen at dislocation cores were characterised by DLTS and LDLTS. Results show the presence of a deep level with complex capture properties. A direct correlation is observed between the DLTS peak height of this level and the amount of oxygen at the dislocation core. Laplace DLTS was used to resolve broad DLTS peaks into numerous emission rates. The fill pulse dependency tests revealed that certain emission rates are not affected by the long range Coulomb forces due to neighbouring states. This suggests that certain emission rates contained in the broad DLTS peaks may be associated with point defects which are not in the vicinity of dislocations. In comparison to silicon, the deep level characterisation of GaN using DLTS and Laplace DLTS is still in its infancy. In this work, the application of DLTS to n-type hexagonal GaN Schottky diodes has revealed a shallow donor level, a series of deep electron traps and a thermally activated metastable hole trap. The dominant deep electron level is shown to emit around room temperature. DLTS and Laplace DLTS results indicate that this level exhibits local band-bending and is likely to arise from dislocations. Laplace DLTS of electron traps has shown that the broad DLTS emission is made up of numerous emission rates. Some of these emission rates do not exhibit fill pulse dependency and could arise from point defects in the strain field of dislocations. If the sample is heated to 600K and cooled down, the subsequent DLTS spectrum displays a dominant negative peak due to hole emission. The spectrum recovers to its original state showing only electron traps if the sample is not electrically characterised for a period of several days or a week, depending on the sample. The formation of this level results in a significant drop in carrier density. It is discussed with reference to the gallium vacancy and its complexes with oxygen donors.

Some of the effects of implanting tellurium and tin into single crystal gallium arsenide are described in this thesis. The distribution and retention of tellurium and tin implanted into GaAs, the properties of the ion implantation damage and the. electrical properties of the ion implanted impurities were studied as a function of the implantation temperature, dose and anneal temperature between 150°C and 700°C. Silicon dioxide (SiO[2]) was used as the encapsulant for the majority of those specimens annealed at temperatures in excess of 500°C. A few comparative measurements were made with silicon nitride (Si[3]N[4]) as the encapsulant material. The effectiveness of silicon dioxide as an encapsulant for GaAs is discussed. The Rutherford backscattering and Hall effect techniques were used to investigate the depth distribution of the physical and electrical properties of the ion implanted layers. It was shown that the damage induced conductivity was confined to a thin surface layer for implantation temperatures of 20°C and 100°C, but deeper diffusing tails in the electrical conductivity versus depth profile were observed for implantation temperatures of 180°C and 250°C. The dependence of the damage induced conductivity on analysis temperature could be described theoretically by a model in which it was assumed that the conduction mechanism was similar to that of an amorphous semiconductor with a non-uniform density of states in the region of the Fermi energy level. Although the ion implanted Te does not redistribute for annealing temperatures up to 700°C, the ion implanted Sn diffuses towards the surface of the crystal. The results presented indicate that, for anneal temperatures up to 700°C, only a small percentage of the ion implanted Te and Sn became electrically active. The reasons for this low activity are discussed.

This thesis is concerned with the formation, assessment, and application of surface layers in a semiconductor, A surface layer is defined to be a layer substantially the whole of which controls the potential distribution and electric field at the surface of a semiconductor, As such, it is very shallow, typically 100A deep. Two methods of doping surface layers are considered, firstly direct implantation of impurities at low energies and secondly recoil implantation of impurities from a thin film. The profiles arising from these two approaches are predicted particularly for the preferred system of antimony in silicon. Assessment techniques based on the metal-semiconductor (Schottky) barrier are developed with the aim of relating the total current passing through a Schottky barrier to the total electrical activity in a surface layer. This is shown to be a particularly powerful technique when the distribution of impurities is symmetrical about a point below the surface. Electrical assessment of surface layers formed by direct implantation of antimony at energies in the range 5-15keV are reported as well as results on layers formed by recoil implantation from an antimony film using either krypton or neon bombardment. Rutherford backscattering measurements are used to monitor such things as recoil yield and inert gas retention and using backscattering at 'glancing incidence' to increase the depth resolution, relevant features of directly implanted surface layers are obtained. Having formed surface layers they are then applied to the Schottky barrier system. It is shown that using surface layers to control the sign and magnitude of the surface field, the effective barrier height of a Schottky diode can be controlled over a wide range and considerable flexibility is brought to the system. This can be done without major degradation of any other characteristic of the diode. The unique situation which arises using implanted surface layers enables one to obtain basic information about current transport in the Schottky barrier vital to the assessment techniques mentioned above. In particular, an estimate is made of the tunnelling effective mass in the direction in silicon.

Proton Beam Writing (PBW) is a direct write technique that employs a focused MeV proton beam which is scanned in a pre-determined pattern over a target material which is subsequently electrochemically or chemically etched and developed. The ultimate depth of the structure is determined by the range of the protons in the material and this allows structures to be formed to different depths. PBW has been successfully employed on etchable glasses, polymers, and semiconductor materials such as silicon (Si). This present thesis is a study on the feasibility of PBW in p-type GaAs, and compares experimental results with computer simulations using the Atlas(c) semiconductor device package from SILVACO. It has been established that hole transport is required for the electrochemical etching of GaAs using Tiron (4,5-Dihydroxy-m-benzenedisulfonic acid, di-sodium salt). PBW in GaAs results in carrier removal in the irradiated regions and consequently minimal hole transport (in these regions) during electrochemical etching. As a result the irradiated regions are significantly more etch resistant than the non-irradiated regions. The proton energy, proton fluence, beam current, etch current density, etch area, structural spacing, enclosed structures and post irradiated annealing were investigated. Successful three-dimensional micro structures were produced using PBW in GaAs and the simulation and experimental results are comparable which has helped to give a better understanding of the processes of PBW in GaAs and the subsequent electrochemical etching process. Keywords: Proton Beam Writing, Gallium Arsenide, SILVACO.

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