Berlin 2005 – scientific programme

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HL: Halbleiterphysik

HL 64: Photovoltaik II

HL 64.10: Talk

Wednesday, March 9, 2005, 13:00–13:15, TU P-N202

Analysis of the recombination processes at silicon based heterojunctions by surface photovoltage transient technique — •A. Laades, C. Schubert, R. Stangl, K. v. Maydell, K. Kliefoth, M. Schmidt, and W. Fuhs — Hahn-Meitner-Institut Berlin, Silizium-Photovoltaik, Kekuléstr. 5, D-12489 Berlin

We have studied the decay dynamics of photoinduced excess carriers in silicon heterojunctions with different surface passivation procedures by means of time-resolved surface photovoltage technique. In this method excess carriers are generated by a short laser pulse and their annihilation is monitored through the time decay of the light-induced change in surface potential. The characteristic time constants of the different decay modes correlate well with interface parameters such as interface recombination velocity, effective lifetime and trap-emission times. The primary advantage of the present technique compared to the conventional minority carrier investigation methods is the direct probing of the influence of band bending on the interface recombination. Using silicon substrates with different resistivities, we have shown that with decreasing band bending the recombination at the interface prevails over volume recombination. By decreasing the interface state density or increasing band bending, the time constant in the initial part of the transient, where the excess carrier concentration still exceeds the equilibrium concentration, increases considerably. This is explained by a decrease in the surface recombination velocity, leading to a dominance of volume recombination. In this case, an effective minority carrier lifetime can be extracted from low injection part of the transient.