Impact of Porous Silicon Thickness on Thermoelectric Properties of Silicon-Germanium Alloy Films Produced by Electrochemical Deposition of Germanium into Porous Silicon Matrices Followed by Rapid Thermal Annealing

Abstract

Silicon-germanium alloy films were formed by electrochemical deposition of germanium into porous silicon matrices with thicknesses varying from 1.5 to 10 μm followed by subsequent rapid thermal processing at 950 °C in an inert atmosphere. Study of the fabricated structures using SEM and Raman spectroscopy, as well as measurements of their electrical conductivity and thermoelectric properties revealed that the highest Seebeck coefficient (-505 μV/K at 450 K) and Power Factor (1950 μW/(m·K2) at 400 K) values were obtained  when a 5 μm-thick porous silicon was used as a structural matrix. Under such conditions, an optimal balance between electrical conductivity, structural disorder and electrical insulation from the substrate is achieved due to the presence of a residual porous underlayer, making it possible to maximize the film’s thermoelectric performance. The obtained silicon-germanium alloy films are deemed suitable for the fabrication of both discrete and integrated thermoelectric devices based on monocrystalline silicon substrates.

Keywords: porous silicon, electrochemical deposition, silicon-germanium, Thermoelectric materials, Thin films