Thermoelectric Effects in Current Induced Crystallization of Silicon Microstructures
We have observed melting of nanocrystalline silicon microwires self-heated through single high-amplitude microsecond voltage pulses which leads to growth from melt upon resolidification. The resolidified regions form two single-crystal domains for wires with sub-micrometer widths. The current densities (J) involved in this process are ~ 1-10 MA/cm2 for suspended wires, and ~ 10-100 MA/cm2 for wires on oxide. These extremely high current densities and the resulting high temperatures (~ 1700 K) and temperature gradients (~ 1 K/nm) along the microwires give rise to strong thermoelectric effects. The thermoelectric effects are characterized through capture and analysis of light emission from the self-heated wires biased with lower magnitude AC voltages (J < 5 MA/cm2). The hottest spot on the wires consistently appears closer to the lower potential end for n-type, and the higher potential end for p-type microwires. Experimental light emission profiles are used to verify the linear thermoelectric models and material parameters used for simulations. Good agreement between these experimental and simulated profiles indicates that the linear models can be used to predict the thermal profiles for current induced crystallization of microstructures. However, the linear models are expected to be insufficient to fully explain the thermoelectric processes for higher current densities and stronger thermal gradients that are generated by high-amplitude short duration pulses.
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