Capacitance transient spectroscopy models of coupled trapping kinetics among multiple defect states: Application to the study of trapping kinetics of defects in heavy-ion-damaged silicon

Abstract

We have considered five different models of charge transfer among coupled defect states in semiconductors where the free-carrier density is limited by the density of unoccupied trap levels, as in the case of defectdominated materials. To determine the time dependence of the trap occupancy features, we formulate a set of coupled differential equations that govern charge capture and emission processes for two defect states. A numerical solution assuming model parameters for traps provides features of the trap occupancy as a function of time. A critical comparison is made in occupancy features for different models, primarily categorized as serial ͑hierarchical͒ and parallel mechanisms of charge transfer. The model predictions are successfully applied to a study of trapping kinetics of defects observed in heavily damaged n-type silicon. We show that, in addition to the occurrence of charge redistribution among multiple traps, the major trap in the damaged silicon exists in two metastable configurations, perhaps with negative U ͑Hubbard correlation energy͒, and the stable configuration refers to a midgap compensating center related to a small cluster of self-interstitials. The applicability of our model simulations can be extended to more complex defect systems using a combination of these simple models.

Evidence of metastability with athermal ionization from defect clusters in ion-damaged silicon

“…Recently, we have reported on the occurrence of a metastable defect with two configurations in heavily damaged silicon. 14 In this paper, we report on the observation of a metastability in an ion-damaged crystalline silicon that is significantly different from those reported earlier in two respects. First, the defect energy is observed to deepen progressively on carrier capture, and second, the emission rate of carrier from any relaxed state is nearly temperature independent.…”

“…15,16,14 In our transient experiment, the depletion layer containing the defects is widened to a fixed value under constant capacitance condition using a feedback circuit. Subsequent to trap-filling pulse ͑with Vϭ0͒, the voltage changes occurring due to carrier emission from the defects are monitored as bias transient V(t) that is analyzed using TATS formalism to obtain emission signature of the defect.…”

Deep-level transient spectroscopy of low-energy ion-irradiated silicon

“…10,11 They have formulated a general model of charge transfer among coupled defect states in semiconductors, where the freecarrier density is limited by the density of unoccupied trap levels, and shown, that this model in the special case of the divacancy level in Si, can explain the observed slowing down of the filling time from a few tens of nanoseconds in the low-defect case to the millisecond scale in the case of heavy damage.…”

Unusual features in trap emission characteristics of heavily damaged silicon induced by MeV ion implantation

“…Using TATS, lineshape analysis is quite straightforward to detect any occurrence of non-Debye trap signature. We have demonstrated the efficacy of TATS in a number of studies involving defects in semi-insulating GaAs [17], DX centre in Al x Ga 1−x As [18], ion irradiation induced defects in deep buried layer in Si [8,19,20] etc. In a typical TATS measurement, transient data are acquired over 4 1 2 orders of magnitude in time at a stabilized temperature.…”