Metastablility of Interstitial Clusters in Ion-Damaged Silicon Studied by Isothermal Capacitance Transient Spectroscopy

Abstract

We review our results on trapping kinetics studies at defect clusters in ion damaged silicon studied by depletion layer capacitance transient spectroscopic techniques. Conventional deep level transient spectroscopy (DLTS) studies on as-implanted and low temperature annealed Si show two major peaks corresponding to a divacancy trap and an interstitial cluster related trap. Kinetics of trapping at the clusters has been monitored over several orders of magnitude in time using an isothermal transient spectroscopic technique called time analyzed transient spectroscopy (TATS). Two distinct effects have been observed regarding the metastability of defect clusters in as-implanted and partially annealed samples. Firstly, with the help of higher order TATS used for monitoring the trap occupancy as a function of filling time, we show that charge redistribution among multiple traps occurs at low temperature in as-implanted samples. A detailed analysis of the relative trap occupancies reveals that the interstitial cluster related major trap exists in two metastable configurations, perhaps with negative U (Hubbard correlation energy), and the stable configuration of the defect is a midgap compensating trap. Secondly, in partially annealed samples, we observe a novel metastability of the defect clusters near room temperature where the trap energy progressively deepens with increasing filling time, finally stabilizing for large filling times at a fixed temperature, and the emission rate of carrier from any relaxed state is nearly temperature independent. From the athermal nature of the associated TATS spectra obtained at different temperatures, it is argued that the defect metastability is driven by change in configurational entropy associated with multiple trapping/detrapping process. These results constitute direct experimental evidence of metastability for small interstitial clusters in silicon and opens up opportunities for further studies on this new class of defect. The necessity of using a time domain relaxation spectroscopy such as TATS in the study of metastabilty is demonstrated.