Dislocation related defects in silicon and gallium nitride.

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.