V. A. Romaka

Features of the conduction mechanisms of the n-HfNiSn semiconductor heavily doped with the Co acceptor impurity

The crystalline structure, electron density distribution, energy and kinetic parameters of a HfNi1 − xCoxSn semiconductor heavily doped with a Co acceptor impurity are studied in the ranges T = 80–1620 K and NACo from 9.5 × 1020 cm−3 (at x = 0.05) to 7.6 × 1021 cm−3 (at x = 0.40). It is shown that variations in the activation energy of hopping conduction ɛ3ρ(x) and the modulation amplitudes of continuous energy bands ɛ3α(x) are caused by the appearance of a donor source in the n-type HfNi1 − xCoxSn semiconductor. It is shown that the doping of n-HfNiSn with a Co acceptor impurity is accompanied by a change in the degree of compensation of the semiconductor due to the simultaneous generation of both structural acceptor-type defects during Ni atom substitution with Co atoms and structural donor-type defects during the partial occupation of Ni sites by Sn atoms. The results are discussed within the Shklovskii-Efros model for a heavily doped and compensated semiconductor.

Features of conduction mechanisms in n-HfNiSn semiconductor heavily doped with a Rh acceptor impurity

The crystal structure and electron-density distribution, as well as the energy, kinetic, and magnetic characteristics of n-HfNiSn intermetallic semiconductor heavily doped with a Rh acceptor impurity in the temperature range T = 80–400 K, in the acceptor-concentration range NARh ≈ 9.5 × 1019−1.9 × 1021 cm−3 (x = 0.005–0.10), and in magnetic fields H ≤ 10 kG are investigated. It is established that doping is accompanied by a simultaneous decrease in concentration, the elimination of donor-type structural defects (to x ≈ 0.02), and an increase in the concentration of acceptor-type structural defects (0 < x ≤ 0.10). The dependence of the degree of semiconductor compensation on temperature is revealed. A model of the spatial arrangement of atoms in HfNi1 − xRhxSn is proposed, and the results of calculating the electron structure based on this model agree with the results of investigations of the kinetic and magnetic characteristics of the semiconductor. The results are discussed within the context of the Shklovskii-Efros model for a heavily doped and compensated semiconductor.

Features of conductivity of the intermetallic semiconductor n-ZrNiSn heavily doped with a Bi donor impurity

The crystal structure, distribution of the electron density of states, and the energy, kinetic, and magnetic properties of the intermetallic semiconductor n-ZrNiSn heavily doped with a Bi donor impurity have been investigated in the ranges T = 80−400 K, NDBi ≈ 9.5 × 1019cm−3 (x = 0.005)−1.9 × 1021 cm−3 (x = 0.10), and H ≤ 0.5 T. It has been established that such doping generates two types of donor-like structural defects in the crystal, which manifest themselves in both the dependence of the variation in the unit cell parameter a(x) and temperature dependence of resistivity lnρ(1/T) of ZrNiSn1 − xBix (x = 0.005). It is shown that ZrNiSn1 − xBix is a new promising thermoelectric material, which converts thermal energy to electric energy much more effectively as compared to n-ZrNiSn. The results obtained are discussed within the Shklovskii-Efros model of a heavily doped and strongly compensated semiconductor.

Features of the band structure and conduction mechanisms of n-HfNiSn semiconductor heavily Lu-doped

The crystal and electronic structures, energy, kinetic, and magnetic characteristics of n-HfNiSn semiconductor heavily doped with a Lu acceptor impurity in the ranges T = 80–400 K and NALu ≈ 1.9 × 1020−1.9 × 1021 cm−3 (x = 0.01–0.10) at H ≤ 10 kG is studied. The nature of the structural-defect generation mechanism leading to changes in the band gap and the degree of semiconductor compensation is determined. Its essence is the simultaneous reduction and elimination of donor-type structural defects due to the displacement of ∼1% of Ni atoms from the Hf (4a) site, the generation of acceptor-type structural defects by substituting Ni atoms with Lu atoms at the 4c site, and the generation of donor-type defects such as vacancies at the Sn (4b) site. The results of calculations of the electronic structure of Hf1 − xLuxNiSn are in agreement with experimental data. The results are discussed within the model of a heavily doped and compensated Shklovskii-Efros semiconductor.

Features of the band structure and conduction mechanisms in the n-HfNiSn semiconductor heavily doped with Ru

The crystal and electronic structure and energy and kinetic properties of the n-HfNiSn semiconductor heavily doped with a Ru acceptor impurity are investigated in the temperature and Ru concentration ranges T = 80–400 K and NARu ≈ 9.5 × 1019−5.7 × 1020 cm−3 (x = 0–0.03), respectively. The mechanism of structural-defect generation is established, which changes the band gap and degree of compensation of the semiconductor and consists in the simultaneous concentration reduction and elimination of donor structural defects by means of the displacement of ∼1% of Ni atoms from the Hf (4a) positions, the generation of acceptor structural defects upon the substitution of Ru atoms for Ni atoms in the 4c positions, and the generation of donor defects in the form of vacancies in the Sn (4b) positions. The calculated electronic structure of HfNi1 − xRuxSn is consistent with the experiment. The results obtained are discussed within the Shklovsky-Efros model for a heavily doped and compensated semiconductor.

Effect of the accumulation of excess Ni atoms in the crystal structure of the intermetallic semiconductor n-ZrNiSn

The crystal structure, electron density distribution, and energy, kinetic, and magnetic properties of the n-ZrNiSn intermetallic semiconductor heavily doped with a Ni impurity are investigated. The effect of the accumulation of an excess number of Ni1 + x atoms in tetrahedral interstices of the crystal structure of the semiconductor is found and the donor nature of such structural defects that change the properties of the semiconductor is established. The results obtained are discussed within the Shklovskii-Efros model of a heavily doped and strongly compensated semiconductor.

The mechanism of generation of the donor- and acceptor-type defects in the n-TiNiSn semiconductor heavily doped with Co impurity

Temperature dependences of resistivity, thermoelectric coefficient, and structural characteristics of the n-TiNiSn intermetallic semiconductor heavily doped with Co impurity (the Co concentration NCo ≈ 9.5 × 1019−1.9 × 1021 cm−3) have been studied in the temperature range 80–380 K; the distribution of the electron density of states is also calculated. It is shown that, in TiNi1 − xCoxSn with x < 0.03, the impurity atoms occupy crystallographic sites of atoms Ti and Ni simultaneously and in various proportions and generate the donor and acceptor defects, respectively. It is established that there is a relation between the impurity concentration, the amplitude of a large-scale fluctuation, and also the degree of filling of the potential well of a small-scale fluctuation (fine structure). The results are discussed in the context of the Shklovskiĭ-Éfros model of a heavily doped and compensated semiconductor.

Features of conductivity mechanisms in heavily doped compensated V1–xTixFeSb Semiconductor

The crystal and electronic structure and also the energy and kinetic properties of n-VFeSb semiconductor heavily doped with the Ti acceptor impurity are investigated in the temperature and Ti concentration ranges of T = 4.2–400 K and NATi ≈ 9.5 × 1019–3.6 × 1021 cm–3 (x = 0.005–0.20), respectively. The complex mechanism of the generation of acceptor and donor structural defects is established. It is demonstrated that the presence of vacancies at Sb atomic sites in n-VFeSb gives rise to donor structural defects (“a priori doping”). Substitution of the Ti dopant for V in VFeSb leads simultaneously to the generation of acceptortype structural defects, a decrease in the number of donor defects, and their removal in the concentration range of 0 ≤ x ≤ 0.03 via the occupation of vacancies by Sb atoms, and the generation of donor defects due to the occurrence of vacancies and an increase in their number. The result obtained underlies the technique for fabricating new n-VFeSb-based thermoelectric materials. The results are discussed in the context of the Shklovsky–Efros model for a heavily doped compensated semiconductor.

Дослідження структурних, термодинамічних та енергетичних характеристик твердого розчину ZrNi1-xRhxSn

The peculiarities of crystal and electronic structures, thermodynamic and energy state characteristics of the ZrNi 1- x Rh x Sn semiconductive solid solution were investigated. It has been shown that in the ZrNiSn compound simultaneously exist two types of structural defects of the donor nature which generate two donor bands with different ionization energy in the band gap: a) the donor band ɛ D 1 , formed as a result of a partial, up to ~ 1%, occupation of 4 a position of Zr atoms by Ni atoms (mechanism of “a priori doping”) and deep donor band ɛ D 2 , formed as a result of partial occupation of the tetrahedral voids by Ni atoms (Vac). The substitution in 4 c position of the Ni atoms by Rh ones in ZrNi 1- x Rh x Sn generates structural defects of acceptor nature and creates an impurity acceptor band ɛ A in the band gap, which, in addition to the existence of ɛ D 1 та ɛ D 2 donor bands, makes semiconductor highly doped and strongly compensated. The obtained results allow to understand the mechanisms of electrical conductivity of thermoelectric materials based on n -ZrNiSn and the ways of conscious optimization of their characteristics for obtaining the maximum efficiency of conversion of thermal energy into electric.

Mechanism of the Generation of Donor–Acceptor Pairs in Heavily Doped n-ZrNiSn with the Ga Acceptor Impurity

The nature of the mechanism of the simultaneous generation of donor–acceptor pairs under heavy doping of n-ZrNiSn intermetallic semiconductor with the Ga acceptor impurity is established. Such spatial arrangement in the crystal lattice of ZrNiSn1–xGax is found when the rate of movement of the Fermi level εF found from calculations of the density distribution of electron states coincides with that experimentally established from dependences lnρ(1/T). It is shown that when the Ga impurity atom (4s24p1) occupies the 4b sites of Sn atoms (5s25p2), structural defects of both acceptor nature and donor nature in the form of vacancies in the 4b site are simultaneously generated. The results are discussed in the scope of the Shklovskii–Efros model of a heavily doped and compensated semiconductor.