Defect Relaxation Dynamics in Amorphous Silicon

Abstract

Using transient capacitance and transient spin techniques, we have the determined the manner in which the mobility gap energy of the D defect is altered following a change in its charge state. This relaxation process gives rise to a power law rather an exponential thermal release of defect electrons with time and also causes the charge emission and spin transients to obey a scaling law. We also deduce that the D°/D+ transition rate depends on the tenure of the proceeding D-/D° transition. This last aspect of the D defect emission behavior implies that it must be treated as a non-Markovian process. Such relaxation dynamics have profound consequences for the steady state distribution of D defect energies. Using the relaxation parameters determined by the transient measurements we have been able to solve a set of coupled differential equations under steady-state conditions to provide the energy distributions of both the D° and DD+ defect sub-bands. The results of these calculations agree remarkably well with the experimental distributions determined by modulated photocurrent and steady-state capacitance measurements. This implies that the statistical variations in the occupation history of the defect may be the dominant factor determining both distributions.