Thermal conduction in doped single-crystal silicon films

This work measures the thermal conductivities along free-standing silicon layers doped with boron and phosphorus at concentrations ranging from ${\text{1×10}}^{17}$ to ${\text{3×10}}^{19}$ ${\mathrm{cm}}^{\text{−3}}$ at temperatures between $15$ and $300$ K. The impurity concentrations are measured using secondary ion mass spectroscopy (SIMS) and the thermal conductivity data are interpreted using phonon transport theory accounting for scattering on impurities, free electrons, and the layer boundaries. Phonon-boundary scattering in the 3-μm-thick layers reduces the thermal conductivity of the layers at low temperatures regardless of the level of impurity concentration. The present data suggest that unintentional impurities may have strongly reduced the conductivities reported previously for bulk samples, for which impurity concentrations were determined from the electrical resistivity rather than from SIMS data. This work illustrates the combined effects of phonon interactions with impurities, free electrons, and material interfaces, which can be particularly important in semiconductor devices.