Investigation of the valence band structure of PbSe by optical and transport measurement

We investigated the valence band structure of PbSe by a combined study of the optical and transport properties of p-type Pb_1-xNa_xSe, with Na concentrations ranging from 0-4%, yielding carrier densities in a wide range of 10¹⁸ - 10²⁰ cm^-3. Room temperature infrared reflectivity studies showed that the susceptibility (or conductivity) effective mass m* increases from ∼ 0.06m_o to ∼ 0.5m_o on increasing Na content from 0.08% to 3%. The Seebeck coefficient scales with doping in the whole temperature range, yielding lower values for higher Na contents, while the Hall coefficient increases on heating from room temperature showing a peak close to 650 K. The room temperature Pisarenko plot is well described by the simple parabolic band model up to ∼ 1·10²⁰ cm^-3. In order to describe the behaviour in the whole concentration range, the application of the two band model, i.e. light hole and heavy hole, was used giving density of states effective masses 0.28m_o and 2.5m_o for the two bands respectively.