Tuning the Thermoelectric Properties of Boron-Doped Silicon Nanowires Integrated into a Micro-Harvester

Semiconductor nanowires demonstrate outstanding properties within a wide range of application fields, including energy harvesting. Consequently, increasing attention has been focused on silicon nanowires for thermoelectric power generation after their successful implementation in miniaturized devices. In this work, the effect of tuning the p-type doping level in silicon nanowires is studied in thermoelectric micro-generators. In situ heavily boron-doped silicon nanowires are grown by the vapor-liquid-solid mechanism in a chemical vapor deposition reactor. Variable quantities of dopant gas-diborane or B2H6-are used to control the doping level and study the direct influence on the thermoelectric properties of the nanowires. The relationship between dopant partial pressure and resulting carrier concentration is evaluated, and all thermoelectric properties are studied as a function of each doping level. A maximum power factor of 2.0 +/- 0.2 mW mK(-2) is found for a carrier concentration of 2.5 x 10(19) cm(-3), corresponding to a figure of merit of zT = 0.04 at near room temperature. Optimized nanowires are included in a micro-machined thermoelectric generator, yielding an open circuit voltage of 4.5 mV and maximum power output of 1.08 mu W cm(-2) upon hot surfaces at 250 degrees C.