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

Abstract

We have investigated the electrical characteristicsof defects in heavily damaged silicon induced by MeV ionimplantation at high doses, by extending the scope of depletionlayer capacitance transient techniques. The heavily damagedlayer is embedded in the depletion layer of a Schottky diode andhigh-frequency capacitance measurements are carried out toevaluate charge relaxation kinetics of defects specific to high-dose implantation. Deep-level transient spectroscopy ofas-implanted silicon shows presence of the divacancy trap(V2) and relatively high concentration of a damage-relatedtrap (D1) with unusual spectral lineshape. Thermally stimulatedcapacitance spectra show large capacitance step even withoutapplication of a trap-filling pulse. Constant-capacitance time-analysed transient spectroscopy studies of the D1 peakreveal that the skewed peakshape is due to premature termination of thetransient signal during trap emission. Strong temperature dependence ofspectral lineshape, ranging from broad to narrow peak (stronger thanthat expected from exponential transient), and trap occupancypoints to a dynamic interdependence of trap occupancy andquasi-Fermi level. Unusual features in spectral lineshape aresimulated by introducing a time-dependent capture term into therate equations for trapping dynamics for a single trap leveland provide strong support for our model on the dynamicinterdependence of quasi-Fermi level and trap occupancy. Thedefect parameter is found to be sensitive to implantation doseand low-temperature annealing. The D1 trap is ascribed to smallself-interstitial clusters.