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Injection-dependent minority carrier lifetime measurements are a valuable characterisation method for semiconductor materials, particularly those for photovoltaic applications. For a sample containing defects which obey Shockley-Read-Hall statistics, it is possible to use such measurements to determine (i) the location of energy levels within the band-gap and (ii) the ratios of the capture coefficients for electrons and holes. In this paper, we discuss a convenient methodology for determining these parameters from lifetime data. Minority carrier lifetime is expressed as a linear function of the ratio of the total electron concentration to the total hole concentration for p-type (or vice versa for n-type) material. When this is plotted on linear scales, a single-level Shockley-Read-Hall centre manifests itself as a straight line. The gradient and intercepts of such a plot can be used to determine recombination parameters. The formulation is particularly instructive when multiple states are recombination-active in a sample. To illustrate this, we consider oxide precipitates in silicon as a case study and analyse lifetime data for a wide variety of p-type and n-type samples as a function of temperature. We fit the data using both a single two-level defect and two independent single-level defects and find the latter can fit the lifetime curves in all cases studied. The first defect is at E V þ 0.22 eV and has a capture coefficient for electrons $157 times greater than that for holes at room temperature. The second defect is at E C À 0.08 eV and has a capture coefficient for holes $1200 times greater than that for electrons at room temperature. We find that the presence of dislocations and stacking faults around the precipitates acts to increase the density of both states without introducing new levels. Using the analysis method described, we present a parameterisation of the minority carrier lifetime in silicon containing oxide precipitates. V

Transient and quasi-steady-state photoconductance methods were used to measure minority carrier lifetime in ∼10 Ω cm p-type Czochralski silicon processed in very clean conditions to contain oxide precipitates. The nucleation and growth times for precipitation were varied to produce 35 samples, which were then characterised by chemical etching and transmission electron microscopy to determine the density and morphology of the precipitates. The effects of other known recombination mechanisms (band-to-band, Coulomb-enhanced Auger, iron-related, and boron-oxygen related) were factored out to isolate the lifetime component associated with the precipitates as accurately as possible. In the samples processed to contain mainly unstrained precipitates, it was shown that the lifetime component due to the precipitates could be extremely high (up to ∼4.5 ms). Recombination at unstrained precipitates is weak and it is estimated that the capture coefficient lies between 3 × 10−8 cm3 s−1 and 1.3 × 10−7 cm3 s−1 at an injection level corresponding to half the doping level. Strained precipitates act as strong recombination centres with a capture coefficient of ∼1 × 10−6 cm3 s−1 at the same level of injection. For the samples investigated, the effective capture coefficient is increased by a factor of ∼3 to 4 when other extended defects (such as dislocations and stacking faults) accompany the strained precipitates. The shape of the injection level dependence of lifetime was similar for all the specimens studied, with the magnitude of the lifetime being dependent on the precipitate density and strain state but approximately independent of precipitate size.

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