Abstract
This work describes tin-induced crystallization of amorphous silicon studied with Raman spectroscopy in thin-film structures Si-Sn-Si irradiated with pulsed laser light. We have found and analyzed dependencies of the nanocrystals’ size and concentration on the laser pulse intensity for 10 ns and 150 μm duration laser pulses at the wavelengths of 535 nm and 1070 nm. Efficient transformation of the amorphous silicon into a crystalline phase during the 10 ns time interval of the acting laser pulse in the 200 nm thickness films of the amorphous silicon was demonstrated. The results were analyzed theoretically by modeling the spatial and temporal distribution of temperature in the amorphous silicon sample within the laser spot location. Simulations confirmed importance of light absorption depth (irradiation wavelength) in formation and evolution of the temperature profile that affects the crystallization processes in irradiated structures.
Highlights
Layered composites utilizing nanocrystalline silicon dispersed within an amorphous Si matrix are considered to be very promising for the generation of quantum dotsbased solar cells [1]
The spectra of samples #7 and #8 prior to laser irradiation treatment revealed only a broad band with a maximum centered around 475 cm−1, which is a characteristic of α-Si [24]
This phase was formed as a result of metal-induced crystallization (MIC) from the amorphous Si phase, in which the nc-Si phase formation was facilitated by laser irradiation [23]
Summary
Layered composites utilizing nanocrystalline silicon dispersed within an amorphous Si matrix are considered to be very promising for the generation of quantum dotsbased solar cells [1] Such composites (referred to as nc-Si in the text below) pose a number of properties important for the photoelectric conversion of solar radiation, for example, quasi-direct bandgap mechanism of light absorption, dependence of the energy bandgap on the nanocrystals size, stability against the Stabler-Vronsky effect, and a possibility of manufacturing on flexible substrates. This work focuses on finding the thermal and time evolution parameters of MIC in the interfacial system αSi/Sn, evaluating the role of photoionization processes in Si nanocrystallites formation, and exploring possible advantages of employing a pulsed laser radiation to control the nanocrystals’ size and partial volume during Sn-induced crystallization of α-Si
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