Transient ion-drift-induced capacitance signals in semiconductors

A theoretical model is developed that describes capacitance signals induced by drift of mobile ions in the space charge region of a Schottky diode. Pairing between the diffusing ion and the doping impurities is taken into account. The coupled partial differential equations are resolved numerically and the influence of key parameters on the signal shape is analyzed. Special emphasis is put On those features that enable transient ion-drift- (TID-) induced signals to be distinguished from capacitance transients caused by deep-level carrier emission processes. Relaxation kinetics and reverse bias dependence of the signal shape represent two reliable tools to verify the ion-drift nature of the signals. Methods for extracting quantitative information on both diffusion and pairing properties of the mobile ions are described. The question of whether pairing or diffusion is limiting the process is addressed. The influence of the doping level on the signal time constant is used to evaluate whether or not the diffusion is trap limited. A semiempirical model is described that permits the estimation of diffusion and pairing coefficients without resolving numerically the differential equations. Experiments are performed on interstitial copper in p-type silicon to test the predictions of the theoretical model. An overall agreement is found between theory and experiments.