Recently, a simple yet powerful carrier lifetime technique for semiconductor wafers has been introduced that is based on the simultaneous measurement of the light-induced photoconductance of the sample and the corresponding light intensity [Appl. Phys. Lett. 69, 2510 (1996)]. In combination with a light pulse from a flash lamp, this method allows the injection level dependent determination of the effective carrier lifetime in the quasi-steady-state mode as well as the quasi-transient mode. For both cases, approximate solutions (those for steady-state and transient conditions) of the underlying semiconductor equations have been used. However, depending on the actual lifetime value and the time dependence of the flash lamp, specific systematic errors in the effective carrier lifetime arise from the involved approximations. In this work, we present a generalized analysis that avoids these approximations and hence substantially extends the applicability of the quasi-steady-state and quasi-transient methods beyond their previous limits.
The carrier recombination lifetime in light-degraded boron-doped 1 Ω cm Czochralski-grown silicon wafers is measured as a function of the bulk excess carrier concentration Δn. The measurements are performed with the quasi-steady state photoconductance method and cover a large injection level range between 1013 and 1.5×1017 cm−3. We observe a very strong increase of the carrier lifetime in the Δn range between 1014 and 2×1016 cm−3, which is attributed to boron–oxygen (BiOi) defect pairs. The observed strong increase of the defect-related carrier lifetime allows us to determine the previously unknown hole capture cross section σp of the BiOi pair. Our analysis gives a σp value of (0.45–1.2)×10−15 cm2, which is 2–3 orders of magnitude smaller than the corresponding electron capture cross section.
The transfer of thin monocrystalline silicon films to foreign substrates is of great interest for a number of applications such as silicon on insulator devices, active matrix displays and thin film solar cells. We present a transfer approach for the fabrication of monocrystalline Si films on foreign substrates based on the formation ofquasi-monocrystallineSi-films. Our transfer approach is compatible with high temperature processing such as epitaxial growth at 1100°C, thermal oxidation and phosphorous diffusion. Reuse of Si host wafers is demonstrated by the subsequent epitaxial growth of three monocrystalline Si films on a single host wafer. Monocrystalline Si films with a thickness of 15 µm and a diameter of 3” are transferred to glass and flexible plastic substrates. The typical light point defect density in films transferred from virgin wafers ranges between 10 to 100 cm−2, while stacking fault and dislocation densities are ≤ 100 cm−2. The minority carrier diffusion length in the epitaxial Si films is around 50 µm.
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