ICT2014 Abstracts

It is well known that PbSe possesses a complex valence band structure showing two maxima; the primary, located at the L point and a secondary located at the Σ point of the Brillouin zone respectively. In this report, we systematically investigate the transport properties of p-type Pb_1-xNa_xSe, with carrier densities in a range of 10¹⁸ – 10²⁰ cm^-3. We show that up to carrier densities ~ 1·10²⁰ cm^-3 the room temperature Pisarenko plot may be explained by a single non-parabolic band with a density of states mass 0.28m_o accounting for the acoustic phonon scattering. For higher carrier concentrations the thermoelectric power is found to be saturated. A two band model can describe the room temperature Seebeck in the whole concentration range, where a second valence band located ~ 0.26 eV below the primary band and high mass (~ 4.5m_o) is considered. On the other hand, the room temperature carrier dependence Hall mobility was found to be well described by a single non-parabolic band in the whole concentration range. The temperature dependent Hall coefficient indicates the redistribution of carriers between the two bands and the convergence of the two bands at temperatures higher than 650 K. The Hall mobility indicates that the decrease with rising temperature follows the law µ~ T^-b. In the temperature range 300 – 500 K the mobility slope was found to decrease progressively upon increasing doping reaching a value of ~ 0.3 for the most heavily doped composition, a situation that may suggest mixed carrier scattering mechanism. The temperature dependent energy gap between the two valence sub-bands will be presented. The discussion of the tuning of the two bands is extended to the nanostructured p-type PbSe – MSe systems (M = Ca, Sr, Ba) where results have shown ZT ~ 1.3 at 923 K.