Self-heating of silicon microwires: Crystallization and thermoelectric effects
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We describe experiments on self-heating and melting of nanocrystalline silicon microwires using single high-amplitude microsecond voltage pulses, which result in growth of large single-crystal domains upon resolidification. Extremely high current densities (.20 MA/cm2) and consequent 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 direct current/ alternating current voltages. The hottest spot on the wires consistently appears closer to the lower potential end for n-type microwires and to the higher potential end for p-type microwires. The experimental light emission profiles are used to verify the mathematical models and material parameters used for the simulations. Good agreement between experimental and simulated profiles indicates that these models can be used to predict and design optimum geometry and bias conditions for current-induced crystallization of microstructures.
I. INTRODUCTION
Polycrystalline silicon (poly-Si), amorphous silicon (aSi), and nanocrystalline silicon (nc-Si) are commonly used for large-area electronics such as flat panel displays,1 x-ray imaging arrays,2 and solar cells. Currently, a-Si is used in Si thin-film transistors for large-area electronics1 due to its uniformity and low-temperature processing, despite its relatively low electrical carrier mobility.3 There is a growing demand for displays and sensors on larger areas, using flexible and shatter-proof substrates like plastics, that can operate at higher speeds and sensitivities. Large areas require uniformity; flexible substrates require low-temperature processing; and higher speed and sensitivity require use of crystalline material instead of amorphous material. Cost-effective techniques to achieve single-crystal Si on arbitrary substrates will also enable significant technological advancements, such as integration of high performance circuitry with displays or sensor arrays as complete systems. The interest in achieving high-speed circuitry for largearea electronics has motivated studies on crystal growth on glass and plastics,4 transfer of crystalline structures onto glass and plastic substrates, and crystallization of low temperature-deposited Si.1,2,5 Vapor–liquid–solid growth4 of Si nanowires leads to single-crystal structures,6 which are compatible with glass Address all correspondence to these authors. e-mail: [email protected] b) e-mail: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2011.32
a)
J. Mater. Res., Vol. 26, No. 9, May 14, 2011
http://journals.cambridge.org
Downloaded: 11 Mar 2015
and potentially with plastic substrates. The remaining challenges for this approach are related to orientation and placement control. Transfer of single-crystal islands or large areas can be achieved with silicon-on-insulator (SOI) wafers and using layer transf
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