Abstract
The study of thermoelectric properties of crystalline semiconductors with structural defects is of practical interest in the development of radiation-resistant Peltier elements. In this case, the spectrum of energy levels of hydrogen-like impurities and intrinsic point defects in the band gap (energy gap) of crystal plays an important role.The purpose of this work is to analyze the features of the single-electron band model of semiconductors with hopping electron migration both via atoms of hydrogen-like impurities and via their own point triplecharged intrinsic defects in the c- and v-bands, as well as to search for the possibility of their use in the Peltier element in the temperature range, when the transitions of electrons and holes from impurity atoms and/or intrinsic defects to the c- and v-bands can be neglected.For Peltier elements with electron hopping migration we propose: (i) an h-diode containing |d1)and |d2)-regions with hydrogen-like donors of two types in the charge states (0) and (+1) and compensating them hydrogen-like acceptors in the charge state (−1); (ii) a homogeneous semiconductor containing intrinsic t-defects in the charge states (−1, 0, +1), as well as ions of donors and acceptors to control the distribution of t-defects over the charge states. The band diagrams of the proposed Peltier elements in equilibrium and upon excitation of a stationary hopping electric current are analyzed.A model of the h-diode containing hydrogen-like donors of two types |d1) and |d2) with hopping migration of electrons between them for 50 % compensation by acceptors is considered. It is shown that in the case of the reverse (forward) electrical bias of the diode, the cooling (heating) of the region of the electric double layer between |d1)and |d2)-regions is possible.A Peltier element based on a semiconductor with point t-defects is considered. It is assumed that the temperature and the concentration of ions of hydrogen-like acceptors and donors are to assure all t-defects to be in the charge state (0). It is shown that in such an element it is possible to cool down the metal-semiconductor contact under a negative electric potential and to heat up the opposite contact under a positive potential.
Highlights
Thermoelectric phenomena in semiconductor systems caused by the migration of electrons in the c-band and holes in the v-band are intensively studied
The efficiency of semiconductor materials used in thermoelectric converters is determined by the dimensionless thermoelectric figure of merit ZT and by the Peltier coefficient Π: ZT = σS 2T ; Π = ST, (1)
There are various ways to increase the thermoelectric figure of merit: selection of the optimal concentration of mobile charge carriers in homogeneous materials; selection of the optimal band gap; changing the chemical composition of materials (e. g., by chemical doping or neutron transmutation doping) or modifying their structure by introducing, for example, radiation defects
Summary
Thermoelectric phenomena in semiconductor systems caused by the migration of electrons in the c-band and holes in the v-band are intensively studied (see, e. g., [1,2,3,4,5,6,7]). Let us briefly consider the possible arrangements of the energy levels of impurity atoms (hydrogen-like donors of two types) or intrinsic point triple-charged defects of the crystal structure in the band gap of semiconductors, suitable for the development of Peltier elements on their basis. When an electrical bias is applied (Figure 2b; U ≠ 0), in the region of contact under a negative potential a thermally stimulated transition of electron from a metal to a semiconductor occurs and the heat Qab ≈ Δt is absorbed, which is necessary to overcome the energy difference between the upper level of t-defect Et2 and the Fermi level EF2 in metal. A decrease in the thermal conductivity of a Peltier element occurs due to the creation in a semiconductor material (working substance) of a sufficiently large (for realization of electron hopping) number of point defects of structure, which effectively scatter phonons (both optical and acoustic) of all wavelengths [55]. At cryogenic temperatures, the thermal conductivity of amorphous SiO2 is much lower than the thermal conductivity of crystalline SiO2 [56]
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