Generalized procedure to determine the dependence of steady-state photoconductance lifetime on the occupation of multiple defects

Abstract

We present a procedure to determine the dependence of photoconductance lifetime on the occupation of multiple defects. The procedure requires numerical iteration, making it more cumbersome than the analytical equations available for single-defect and simplified two-defect cases, but enabling the following features: ͑i͒ it accounts for the defect concentration when calculating the equilibrium carrier concentrations, ͑ii͒ it permits recombination through any number of defects, ͑iii͒ it calculates the occupation fraction of all defects at any injection, and ͑iv͒ it promotes a good understanding of the role of defect occupation in photoconductance measurements. The utility of the numerical procedure is demonstrated on an experimental sample containing multiple defects. The dependence of the sample's photoconductance on carrier concentration and temperature can be qualitatively described by the generalized procedure but not by either analytical model. The example also demonstrates that the influence of defect occupation on photoconductance lifetime measurements is mitigated at elevated temperatures-a conclusion of particular worth to the study of multicrystalline silicon.

Temperature dependent carrier lifetime studies on Ti-doped multicrystalline silicon

“…12 However, for the temperature range above 100°C, the trapping effect was removed since the traps become filled with thermally generated carriers. 12,13 The effective lifetime of the Ti-contaminated wafer was found to be only about seven times less than the effective lifetime of the control wafer taken from a similar position in the ingot, as depicted in Fig. 1.…”

Trapping-related recombination of charge carriers in silicon

“…Trapping-related recombination of charge carriers in silicon N. P. Harder, 1,2,a͒ R. Gogolin, 1 4 have shown that the temperature dependence of the trapping-effect in the apparent lifetime signal can be much more adequately described by allowing for nonzero, yet nevertheless very small, majority carrier capture cross sections. This is essentially equivalent to using the Shockley-Read-Hall ͑SRH, Refs.…”

“…2͑a͒ includes the fit curves of Fig. 4. In order to fit the reduced PL carrier lifetime at low injection we have to introduce a type of third defect with long high-injection lifetime and very short low-injection lifetime.…”

Simulations of photoconductivity and lifetime for steady state and nonsteady state measurements

“…McIntosh et al 3 presented a procedure to overcome most of these restrictions. Their model, however, is only valid for steady state measurements, a constant mobility, and it does not account for temperature dependent capture cross sections.…”