A model for the high-temperature transport properties of heavily doped n-type silicon-germanium alloys

Abstract

A model is presented for the high-temperature transport properties of large-grain-size, heavily doped n-type silicon-germanium alloys. Electron and phonon transport coefficients are calculated using standard Boltzmann equation expressions in the relaxation time approximation. Good agreement with experiment is found by considering acoustic phonon and ionized impurity scattering for electrons, and phonon-phonon, point defect, and electron-phonon scattering for phonons. The parameters describing electron transport in heavily doped and lightly doped materials are significantly different and suggest that most carriers in heavily doped materials are in a band formed largely from impurity states. The maximum dimensionless thermoelectric figure of merit for single-crystal, n-type Si0.8Ge0.2 at 1300 K is estimated at ZT≂1.13 with an optimum carrier concentration of n≂2.9×1020 cm−3.

High-temperature thermoelectric response of double-dopedSrTiO3epitaxial films

“…The power law exponent reported in the literature varies from 1.5-2.7 over a temperature range of 100-1300 K. Tufte et al 25 reported an exponent of 2.7 around 100-400 K. Uematsu et al 26 observed an exponent of 2.0 over a temperature range of 500-1000 K. Moos et al 27 noted a change in the exponent from 2.7 close to room tem- perature to 1.6 above 1000 K. Unlike these observations, Ohta et al 7 reported an exponent of 1.5 over 300-1000 K and correlated the behavior to phonon scattering as observed in classical semiconductors 28 . Previous studies found no dependence of the exponent on the carrier concentration.…”

Tuning the electronic effective mass in double-dopedSrTiO3

“…Typically, more than one scattering mechanism is present over the range of temperature under investigation. The samples containing low La doping (0, 2 or 5%) but with oxygen vacancies showed a constant mobility for temperatures near room temperature, indicating the presence of partially ionized impurity scattering or neutral impurity scattering 24 as the dominant scattering mechanism. In this limit, the transport is dominated by the oxygen vacancies, which ionize partially by localizing some of the electrons.…”

Microstructure and mechanical properties of thermoelectric nanostructured n-type silicon-germanium alloys synthesized employing spark plasma sintering

“…A vast majority of the research done 1,[5][6][7][8] on SiGe TE materials has been focused on their thermal and electrical transport properties primarily aimed towards enhancing their ZT. However, their mechanical properties are equally important for the long term reliability of their TE modules, as these materials are known to be brittle with low fracture toughness.…”

“…Microstructure and mechanical properties of thermoelectric nanostructured n-type silicon-germanium alloys synthesized employing spark plasma sintering Among the several available thermoelectric (TE) materials, SiGe alloys have been identified as one of the most important material for TE power generation, due to their high TE figure-of-merit (ZT), coupled with excellent thermal stability at high temperatures $1000 C. [1][2][3] For about the past four decades, SiGe based thermoelectrics have been used as TE devices for power generation in Radio-isotope TE Generators (RTG) for deep space missions. 4 In the recent past "nanostructuring" has resulted in significantly increasing the ZT of both n-type 5 and p-type 6 Si 80 Ge 20 and thus nanostructured Si 80 Ge 20 are evolving as a potential replacement for their conventional bulk counterparts in designing efficient RTGs.…”