Determination of recombination parameters in silicon wafers by transient microwave absorption

Abstract

Principles of measurement of photoconductance transients by time-resolved microwave absorption and reflection mode are presented. The microwave transmission (absorption) mode is a new implementation of the time-resolved microwave conductivity method. This instrument is more sensitive with respect to microwave response signal and less critical to instabilities induced by phase modulation of the response. An adjustment of the measurement system into a local resonance for each particular sample under investigation and the whole set of experimental conditions is crucial to ensure the highest sensitivity and reliability of the instruments. The waveguide slot resonance antenna provides mapping of recombination parameters in silicon wafers of thickness d≥50 μm and resistivity ρ≥1 Ω cm with a spatial resolution of 1–2 mm. Theoretical models and validity of the approximations for carrier decay analysis and determination of the recombination parameters are discussed. The nonlinearities of the recombination processes (Shockley–Read–Hall, Auger type, or carrier trapping) arising at the moderate and high level of excitation are analyzed. Determination of the recombination parameters in this case is based on correlated measurements and numerical simulations taking into account the dominant recombination mechanisms. The activation energies of carrier traps Etb=0.16±0.02 eV and Ets=0.20±0.02 eV in neutron transmutation doped n-Si material have been derived from temperature dependent carrier lifetime measurements.