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 N _A ^Rh ≈ 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 HfNi_{1 ? x} Rh _x Sn 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 the mechanisms of generation and “Healing” of structural defects in the heavily doped intermetallic semiconductor n-ZrNiSn

The crystal structure, density of electron states, and charge-transport characteristics of an intermetallic semiconductor ZrNiSn heavily doped with acceptor impurity Y (N _A ^Y ≈ 3.8 × 10²⁰?4.8 × 10²¹ cm^?3) have been studied in the temperature range T = 80–380 K. Relation between the impurity concentration and the amplitude of a large-scale fluctuation and also the degree of occupation of the potential well of small-scale fluctuation by charge carriers (fine structure) is established. The results are discussed in 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, N _D ^Bi ?? 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 ln??(1/T) of ZrNiSn_{1 ? x} Bi _x (x = 0.005). It is shown that ZrNiSn_{1 ? x} Bi _x 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.     

The mechanism of generation of the donor- and acceptor-type defects in the <Emphasis Type="Italic">n</Emphasis>-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 N ^Co ≈ 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 TiNi^{1 − x} Co _x Sn 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.     

Recombination and trapping centers in pure and doped TlBr crystals

TlBr is a promising wide-gap semiconductor for developing γ-radiation detectors. One of the limiting factors in developing the technology of detectors is the lack of experimentally determined trapping and recombination centers. In this paper, a generalized model of the formation and behavior of intrinsic defects in pure and doped TlBr single crystals is presented. The relation of intrinsic defects to growth conditions and electrical properties is determined. The previously obtained temperature dependences of the photoconductivity, the data of current deep level transient spectroscopy and microcathodoluminescence, and the kinetic characteristics of the photoconductivity are used as objects of analysis. It is shown that the compensation of charged centers control the transport properties of charge carriers. In compensated doped TlBr crystals, the product of the mobility and lifetime can reach μτ = 5 × 10^?4 cm² V^?1. The energy-level diagram of local levels in pure and doped TlBr crystals is proposed. The ionization energies of major structural and impurity defects in TlBr, i.e., the anion vacancy V _a ⁺ , cation vacancy V _c ^? , and Pb²⁺, O^2?, S^2? ions, are determined. The energy position of a single anion vacancy V _a ⁺ is E _c ? 0.22 eV. The energy level of the cation vacancy is E _v + 0.85 eV for a single cation vacancy and E _v + 0.58 eV for a vacancy incorporated into the {Pb²⁺ V _c ^? }⁰ complex. The ionization energy of the Pb²⁺ Coulomb trap is E _c ? 0.08 eV in doped TlBr crystals.     

Mechanism of local amorphization of a heavily doped Ti1 − x V x CoSb intermetallic semiconductor

Structural and electron transport characteristics of a TiCoSb intermetallic semiconductor heavily doped with the V donor impurity (dopant concentration ～9.5 × 10¹⁹ ? 1.9 × 10²¹ cm^?3, temperatures 80–380 K) have been investigated and the distribution of the electron density of states in this material has been calculated. Different occupancies have been established for Co and (Ti, V) atomic positions in the Ti_{1 ? x} V _x CoSb lattice; this difference is equivalent to introduction of two types of acceptors into the semiconductor. Suppression of the metallic conductivity in the n-type semiconductor with an increase in the donor concentration has been found, which is explained by simultaneous generation of acceptors. It is shown that the methods of numerical calculation adequately describe the physical processes if the occupancy of unit-cell positions is taken into account in construction of the Wigner-Seitz lattice. The results obtained are discussed within the model of a heavily doped and compensated Shklovskii-Efros semiconductor.     

Effects of Cooling Rate and Composition on Mechanical Properties of Directionally Solidified Pb100?x -Sn x Solders

Pb_100?x -Sn _x solders (x = 5 wt.%, 10 wt.%, 20 wt.%, 35 wt.%, 50 wt.%, 60 wt.%, 61.9 wt.%, and 95 wt.%) were directionally solidified upward over a wide range of cooling rates $ \dot{T} $ (0.016 K s^?1 to 4.0 K s^?1) by using a Bridgman-type directional solidification furnace. Microstructure parameters (primary dendrite arm spacing, ?? ₁, and eutectic spacing, ?? _E) and mechanical properties (microhardness, HV, and ultimate tensile strength, ??) of the Pb_100?x -Sn _x alloys were measured. The dependences of the microhardness and ultimate tensile strength on the cooling rate, microstructure parameters, and composition were determined. According to experimental results, the microhardness and ultimate tensile strength of the solidified samples increase with increasing cooling rate and Sn content, but decrease with increasing microstructure parameters.     

Electrical characteristics of CdTe:Pb single crystals at high temperatures

The electrical properties of CdTe:Pb single crystals at high temperatures (400–900°C) and under controlled Cd vapor pressure (0.001–3 atm) were investigated for the first time. The temperature and baric dependences of the conductivity and Hall coefficient were measured. Low (in comparison with undoped CdTe) electron concentration indicates an increase in the number of impurity point defects related to the Pb impurity. The results obtained are explained within the Kröger theory of quasi-chemical reactions of defect formation on the assumption that lead may exist in the isolated state (Pb _Cd ⁺ ) and as a component of (Pb _Cd ⁺ V _Cd ^2? )^? associates.     

Specific features of the metal-insulator conductivity transition in narrow-gap semiconductors of the MgAgAs structure type

The role of the impurity acceptor band in the conductivity of the doped and compensated ZrNiSn semiconductor is assessed. A reconstruction model of the impurity band as a result of doping the semiconductor with acceptor impurities is suggested. The electronic structure of the Zr_1?x Sc_xNiSn alloy is calculated. Oscillations of the magnetic susceptibility in the region of the metal-insulator transition (related to the Anderson transition) as the Zr_1?x Sc_xNiSn composition is varied are observed for the first time. These oscillations are believed to be a manifestation of the Coulomb gap in the impurity band as the levels of doping and compensation of the semiconductor are varied.     

Molecular — impurity absorption in KC1 for infrared laser windows

Residual impurity absorption in the 10μm region severely limits the usefulness of KCl as a high-power CO₂ laser window. In order to investigate possible origins for this absorption, KCl was doped with carbonate and hydroxyl impurities, and grown in various atmospheres. Characteristic absorption bands in the infrared and ultraviolet were used to determine relative dopant concentrations. Growth conditions introducing CO/ ₃ ⁼ exclusively, led to relatively low and featureless absorption spectra in the 10.6μm region, while conditions introducing both CO/ ₃ ⁼ and OH⁻ led to enhanced absorption. (Additionally, a correlation is indicated between the strength of absorption at 10.6μm and that of the oxygen band at 0.26μm in samples grown in atmospheres in which oxygen was present). Our observations suggest the possibility of absorption due to CO/ ₃ ^≽ complexes, NO ₃ ⁻ , HCO ₃ ⁻ and/or ClO ₃ ⁻ in the 10μm region. While the effects of ultralow concentration of these impurities remain uncertain, the present results suggest that their presence may well contribute to extrinsic absorption in the 10μm region. Rsch supported by AFCRL(AFSC) - Contr F19628-72-C-0286     

Features of the structural,electrokinetic, and magnetic properties of the heavily doped ZrNiSn semiconductor: Dy acceptor impurity

The structural, energy, electrokinetic, and magnetic characteristics of the intermetallic semiconductor ZrNiSn heavily doped (to 9.5 × 10¹⁹–3.8 × 10²¹ cm^?3) with Dy acceptor impurity have been investigated in the temperature range T = 80–380 K. A relationship has been established between the impurity concentration, large-scale fluctuation amplitude, and the occupancy of the small-scale fluctuation potential well (fine structure) with charge carriers. The results are discussed within the model of heavily doped and compensated Shklovski?-Efros semiconductors.     

Features of electrical conductivity in the <Emphasis Type="Italic">n</Emphasis>-ZrNiSn intermetallic semiconductor heavily doped with the In acceptor impurity

The temperature and concentration dependences of resistivity and thermopower in a heavily doped and highly compensated semiconductor alloy ZrNiSn_1?x In _x in the temperature range T = 80–380 K at x = 0.005–0.15 are studied. It is assumed that the ZrNiSn semiconductor doped heavily with the In acceptor impurity is an amorphous semiconductor. It is experimentally established that there is a proportionality between the parameters of fluctuations in the bands of continuous energies, depth of fluctuations, and the depth of the potential well for a small-scale fluctuation. The conclusion advanced by Shklovski? and Éfros in 1972 [10] is experimentally confirmed for the first time; this conclusion is concerned with the assertion that, in a highly doped and completely compensated semiconductor, the maximum amplitude of fluctuations in the bands of continuous energies is equal to the half width of the band gap of the semiconductor, while the Fermi level is located near the midgap.     

Quantitative calibration and germanium SIMS depth profiling in Ge x Si1 − x /Si heterostructures

Methods for minimizing nonlinear matrix effects in the quantitative determination of germanium concentrations in Ge _x Si_{1 ? x} layers by secondary ion mass spectrometry are discussed. The analysis conditions with positive SiCs⁺, GeCs⁺ and negative Ge^?, Si^? secondary ions produced during sputtering by cesium ions are used in the TOF.SIMS-5 setup with a time-of-flight mass analyzer. In contrast to published works for TOF.SIMS setups, the linear dependence of the ion-concentration ratio Ge^?/Si^? on x/(1 ? x) is shown. Two new linear calibrations for the germanium concentration as a function of the cluster Ge ₂ ^? secondary ion yield are proposed. The calibration factors are determined for all linear calibrations at various energies of sputtered cesium ions and Bi⁺ and probe Bi ₃ ⁺ ions. It is shown for the first time that the best depth resolution among the possible conditions of quantitative germanium depth profiling in Ge _x Si_{1 ? x} /Si multilayer heterostructures is provided by the calibration mode using elemental Ge^? and Si^? negative secondary ions.     

Features of the band structure and conduction mechanisms of <Emphasis Type="Italic">n</Emphasis>-HfNiSn heavily doped with Y

The crystalline and electronic structures, energy, kinetic, and magnetic characteristics of n-HfNiSn semiconductor heavily doped with Y acceptor impurity are studied in the ranges: T = 80–400 K, N _A ^Y ≈ 1.9 × 10²⁰–5.7 × 10²¹ cm^–3 (x = 0.01–0.30), and H ≤ 10 kG. The nature of the mechanism of structural defect generation is determined, which leads to a change in the band gap and the degree of semiconductor compensation, the essence of which is the simultaneous reduction and elimination of structural donor-type defects as a result of the displacement of ~1% of Ni atoms from the Hf (4a) site, and the generation of structural acceptor-type defects by substituting Hf atoms with Y atoms at the 4a site. The results of calculations of the electronic structure of Hf_1–x Y _x NiSn are in agreement with the experimental data. The discussion is performed within the Shklovskii–Efros model of a heavily doped and compensated semiconductor.     

Mechanism of the Generation of Donor–Acceptor Pairs in Heavily Doped <Emphasis Type="Italic">n</Emphasis>-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 ZrNiSn_1–xGa _x 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.     

I–V characteristics and the spectrum width during electron tunneling through nanosandwiches W-WO2-(Au 147 ? )-Al2O3-Al and Nd-Nd2O3-(Au 55 ? )-Nd2O3-Nd. Part I: Quantum-chemical calculation of energies of orbitals for anions of nanoclusters Au55 and Au147

This work is devoted to the investigation of electron tunneling through ??magical?? nanoclusters Au₅₅ and Au₁₄₇. Using the quantum-chemical calculation, it is shown that the energy of the highest occupied molecular orbital (HOMO) level is ${E_{HOMOAu5{5^ - }}} = - 3.2eV$ and E _HOMOAu147 = ?4.4 eV, respectively. It is established that the difference between energy E _LUMO ^? of the lowest unoccupied level LUMO and energy E _LUMO ^? for the anions of clusters (Au ₅₅ ^? and Au ₁₄₇ ^? ) is 0.86 and 0.24 eV, respectively. Based on the results of the calculations, it is assumed that nanosandwiches W-WO₂-(Au ₁₄₇ ^? )-Al₂O₃-Al can be promising structures for implementation of metal nanodiodes based on them, while nanosandwiches Nd-Nd₂O₃-(Au ₅₅ ^? )-Nd₂O₃-Nd can be promising for implementation of energy filters not producing hot electrons and allowing the fabrication of the ring Aharonov-Bohm interferometers based on normal metals at liquid-helium temperatures.     

Features of conductivity mechanisms in heavily doped compensated V<Subscript>1–<Emphasis Type="Italic">x</Emphasis> </Subscript>Ti<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript>FeSb 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 N_A^Ti ≈ 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.     

Injection currents in amorphous alloys of the Se-S system

The study of current-voltage characteristics of amorphous film samples of the Se_1?x S _x system (x = 0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5) showed that carrier transport occurs by the mechanism of one-carrier injection space-charge-limited currents, involving two groups of traps, i.e., shallow ones (E _t1) corresponding to charged intrinsic defects C ₁ ^? and caused by dangling bonds in selenium and deep traps E _t2 also corresponding to charged intrinsic defects _{C 3} ⁺ in selenium. It has been shown that a change in the Se-S system composition significantly affects both the charge transport mechanism and trap parameters, i.e., energy states and concentrations.     

Role of the impurity band during the insulator-metal transition as the composition of highly doped and compensated TiCo1–x NixSb semiconductor alloy is varied. Donor impurities

The role of the impurity donor band in the conductivity of the heavily doped and compensated intermetallic TiCoSb semiconductor is determined. The electronic structure of the TiCo_1–x Ni_xSb semiconductor alloy is calculated. A model of impurity band transformation in the TiCoSb semiconductor due to donor impurity doping is suggested. The transition from activated to metallic conductivity when varying the TiCo_1–x Ni_xSb alloy composition is detected, which we identify with the Anderson transition.     

Point Defects in Pb-, Bi-, and In-Doped CdZnTe Detectors: Deep-Level Transient Spectroscopy (DLTS) Measurements

We studied, by current deep-level transient spectroscopy (I-DLTS), point defects induced in CdZnTe detectors by three dopants: Pb, Bi, and In. Pb-doped CdZnTe detectors have a new acceptor trap at around 0.48?eV. The absence of a V_Cd trap suggests that all Cd vacancies are compensated by Pb interstitials after they form a deep-acceptor complex [[Pb_Cd]⁺-V _Cd ^2? ]^?. Bi-doped CdZnTe detectors had two distinct traps: a shallow trap at around 36?meV and a deep donor trap at around 0.82?eV. In detectors doped with In, we noted three well-known traps: two acceptor levels at around 0.18?eV (A-centers) and 0.31?eV (V_Cd), and a deep trap at around 1.1?eV.