Functionally Graded Ge1–xSix Thermoelectrics by Simultaneous Band Gap and Carrier Density Engineering

Exploiting the material gradients inherent to crystal growth techniques, boron doped Ge 1– x Si x ( x = 0 to ∼0.25) samples graded in both band gap and carrier concentration have been prepared by the Czochralski method. Along the length of the Ge 1– x Si x samples x changes continuously, giving rise to changes in the band gap from 0.87 to 0.65 eV. Similarly, gradients in the boron content results in continuous carrier density changes along the sample. This results in samples graded in several material parameters relevant to thermoelectric performance. The present study thereby demonstrates a one-step method for preparing thermoelectrics graded in both carrier concentration and band gap. By careful matching of dopant and material system, it is demonstrated how the gradient in dopant and band gap can work in synergy and mutually enhance the thermoelectric performance over the individual contributions.