SCHEDULED MAINTENANCE
Controlling the thermoelectric power of silicon–germanium alloys in different crystalline phases by applying high pressure
Abstract
Silicon, germanium and their alloys are classical semiconductors that play an important role in fundamental sciences and are the basis for modern microelectronics, optoelectronics, energy conversion, and other applications. The thermoelectric power (Seebeck coefficient) of p- and n-type materials in combination with the electrical and thermal conductivities characterizes the efficiency of thermal-to-electric energy conversion. In this work we experimentally show how one can effectively control the thermoelectric power of silicon-germanium alloys using an applied high pressure. We measured the Seebeck coefficient and the electrical resistance for several Si1−xGex crystals with different compositions under applied high pressure in (i) their original semiconductor cubic-diamond structure, (ii) across a phase transition to a metal phase at about 9–13 GPa, and (iii) across phase transformations to different metastable phases on pressure release. These studies were carried out for several pressurization and decompression cycles. The Si–Ge samples were examined by X-ray diffraction and Raman spectroscopy. After the high-pressure cycling the Si–Ge samples transformed into two metastable phases, namely, a cubic bc8 phase (Si-III) with a p-type electrical conductivity in the Si-dominant samples, and a tetragonal st12 phase (Ge-III) in the Ge-dominant alloys, whose conductivity type depended on the Si content. The dramatic pressure-driven changes in the thermoelectric power of Si–Ge crystals we found suggest that these semiconductors are promising for use in various stress-controlled electronic junctions, such as switches, p–n diode elements, n–p–n (p–n–p) transistors, and multi-layer heterostructures with alternating types of electrical conductivity.
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