The Spectroscopic Ellipsometry and the Time Resolved Microwave Conductivity (TRMC) are efficient tools for in-situ non invasive characterizations during the growth of semiconductors and interfaces. From ellipsometry, one estimates the optical absorption, structural composition of the material in the bulk and near the interface. The TRMC measures the transient microwave reflectivity induced by carriers photogenerated by a pulsed laser. From TRMC, one may estimate the mobility of the carriers in a thin film or in bulk materials, the carrier lifetime in the bulk or near the surface. Particularly, we characterize microcrystalline silicon: electron and hole mobility, electron mobility inside the grain, trapping. We also analyze the semiconductor/dielectric interface, particularly for c-Si/SiO2. Using various UV laser fluxes, we can characterize the surface recombination, estimate the interface field and compare with the density of states obtained from capacitance measurement. The results are compared with simulation.
Top gate and bottom gate microcrystalline silicon thin film transistors (TFTs) have been produced by the radio frequency glow discharge technique using three preparation methods: the standard hydrogen dilution of silane in hydrogen, the use of the layer-by-layer technique, and the use of SiF4-Ar-H2 feedstock. In all cases, stable top gate TFT with mobility values around 1 cm2/V.s have been achieved, making them suitable for circuit on glass applications. Moreover, the use of SiF4 gas combined with specific treatments of the a-SiN:H dielectric in bottom gate TFTs, fully compatible with today's a-Si:H process, lead to lateral growth of the silicon crystallites and an enhancement of the mobility to reach stable values of around 3 cm2/V.s.
The Spectroscopic Ellipsometry and the Time Resolved Microwave Conductivity (TRMC) are efficient tools for in-situ non invasive characterizations during the growth of semiconductors and interfaces. From ellipsometry, one estimates the optical absorption, structural composition of the material in the bulk and near the interface. The TRMC measures the transient microwave reflectivity induced by carriers photogenerated by a pulsed laser. From TRMC, one may estimate the mobility of the carriers in a thin film or in bulk materials, the carrier lifetime in the bulk or near the surface. Particularly, we characterize microcrystalline silicon : electron and hole mobility, electron mobility inside the grain, trapping.
A new optical instrument allowing photoellipsometric measurements is presented. Photoellipsometry (PE) is a modulation spectroscopy technique which uses ellipsometry in presence of a chopped external light excitation. PE measurements are obtained using a double modulation system, combining spectroscopic phase-modulated ellipsometry (SPME) with a laser pump beam. The experimental system described here takes advantage of the high frequency polarization of SPME (approximately equals 50 kHz). As a consequence the frequency of the pump beam can be varied up to 5 kHz. The field-induced changes in the real and imaginary parts of the bulk dielectric function can be directly measured and analyzed in terms of the pump beam power or the probe beam photon energy. Demonstration of this method is made with measurements, recorded in the band-gap E0 region (approximately equals 1.4 eV), on n-type GaAs sample. In particular, Franz-Keldish oscillations are observed with a very good sensitivity. More generally, PE measurements are compared with a theoretical model. From this preliminary study, it can be concluded that PE appears as a promising technique for semiconductor characterization.
We report the observation in a-Si:H of a large thermal nonlinearity with a picosecond response time. The spectral dependence of the refractive and absorptive parts of this unusually fast thermal nonlinearity reveals that it arises from a picosecond nonradiative recombination of electrons and holes across the band gap. The optical and electronic processes that make this thermal nonlinearity possible and observable are discussed.
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