Bistable amphoteric centers in semiconductors

It is shown that, at thermodynamic equilibrium, the release of charge carriers from the localized states of bistable amphoteric centers into quasi-free states depends on the degree of compensation. This brings about different functional dependences of the concentration of free charge carriers on temperature. It is found that, in uncompensated semiconductors, the concentration of free charge carriers follows the same dependence in the case of bistable amphoteric centers and bistable amphoteric U ^? centers, although the distributions of charge carriers over the charge states and configurations are different for these types of centers. The results can be used for interpreting various experimental data insufficiently explained in the context of the traditional approach.     

Dissociation energies of a C<Subscript>i</Subscript>C<Subscript>s</Subscript> complex and the <Emphasis Type="Italic">A</Emphasis> center in silicon

Reactions of annealing of A centers (VO) and complex centers consisting of interstitial carbon atoms and substitutional carbon atoms (C_iC_s) in n-Si irradiated with fast electrons or ⁶⁰Co gamma quanta were analyzed. The kinetics of isochronous annealing of the above centers was evaluated. By comparing the results of calculations with published experimental data, which were obtained by measuring the concentration of centers with the level E_c?0.17 eV in the course of isochronous heat treatment of irradiated n-Si, the dissociation energy E for the C_iC_s complex was estimated at 1.10±0.05 eV. The activation energy for annealing of this center was found to be equal to \(E_{aC_i C_s } \approx 2.0eV\). The dissociation energy for the A center was estimated at E_A=1.94 eV.     

Mössbauer studies of two-electron centers with negative correlation energy in crystalline and amorphous semiconductors

The results of the study of donor U ^?-centers of tin and germanium in lead chalcogenides by Mössbauer emission spectroscopy are discussed. The published data regarding the identification of amphoteric U ^?-centers of tin in glassy binary arsenic and germanium chalcogenides using Mössbauer emission spectroscopy, and in multicomponent chalcogenide glasses using Mössbauer absorption spectroscopy are considered. Published data concerning the identification of two-atom U ^?-centers of copper in lattices of semimetal copper oxides by Mössbauer emission spectroscopy are analyzed. The published data on the detection of spatial inhomogeneity of the Bose-Einstein condensate in superconducting semiconductors and semimetal compounds, and on the existence of the correlation between the electron density in lattice sites and the superconducting transition temperature are presented. The principal possibility of using Mössbauer U ^?-centers as a tool for studying the Bose-Einstein condensation of electron pairs during the superconducting phase transition in semiconductors and semimetals is considered.     

Energy parameters of two-electron tin centers in PbSe

Relations that make it possible to use an experimentally measured temperature dependence of carrier concentration to determine the Hubbard energy U and temperature dependence of the Fermi level F for two-electron tin centers in lead selenide are derived. A study of Pb_1?x?ySn_xNa_ySe solid solutions shows that their Fermi level in the temperature region 100–600 K lies below the valence band top E _v and that their F(T) dependences are linear, with extrapolation to T = 0 yielding E _V ?F = 210±10 meV. The Hubbard energy of the two-electron tin centers in PbSe is found to be U = ?80±20 meV.     

Electrical properties of silicon layers implanted with erbium and oxygen ions in a wide dose range and thermally treated in different temperature conditions

The electrical properties of silicon implanted with Er and O ions in a wide dose range have been studied. The dependence of electron mobility on the concentration of electrically active centers is determined for Si:Er layers with Er concentrations in the range of 9×10¹⁵–8×10¹⁶ cm^?3. Sharp bends related to specific features of Er segregation in solid-phase epitaxial recrystallization are observed in the concentration profiles of electrically active centers, n(x), and Er atoms, C(x), at Er ion implantation doses exceeding the amorphization threshold. The n(x) and C(x) profiles virtually coincide near the surface. A linear rise in the maximum concentration of electrically active centers at approximately constant effective coefficient of their activation, k, is observed at Er implantation doses exceeding the amorphization threshold. At an Er concentration higher than 7×10¹⁹ cm^?3, the concentration of electrically active centers levels off and k decreases.     

The nature of thermoacceptors in electron-irradiated high-resistance silicon

We have carried out an analysis of the possibility for the deep acceptor centers in silicon to participate in the formation of the thermoacceptor effect observed experimentally in a number of works, which consists in a change of conductivity from the n- to the p-type by annealing after irradiation of high-resistance silicon with electrons or neutrons. Based on the solution of the electroneutrality equation in a compensated monocrystalline silicon, we have estimated the concentration of the deep acceptor centers which are needed for obtaining p-type conductivity depending on the acceptor ionization energy and concentration of a shallow donor impurity. It is shown that deep acceptor centers (with ionization energy of up to 0.4 eV) can substantially contribute to the thermoacceptor effect in high-resistance n-type silicon prepared by floating zone melting. The concentrations of deep acceptors needed to overcompensate a sample with a low initial donor concentration (10¹²–10¹³ cm^–3) are on the order of 10¹²–10¹⁴ cm^–3 and seem to be quite achievable. Such centers can be divacancy–impurity (Fe, P) complexes with the ionization energy of up to 0.34 eV. In this case, the thermal activation of interstitial boron is also not excluded.     

Traps with near-midgap energies at the bonded Si/SiO<Subscript>2</Subscript> interface in silicon-on-insulator structures

Capture centers (traps) are studied in silicon-on-insulator (SOI) structures obtained by bonding and hydrogen-induced stratification. These centers are located at the Si/SiO₂ interface and in the bulk of the split-off Si layer. The parameters of the centers were determined using charge deep-level transient spectroscopy (Q-DLTS) with scanning over the rate window at fixed temperatures. Such a method allows one to study the traps near the Si midgap at temperatures near 295 K. It is shown that the density of traps with a continuous energy spectrum, which are located at the bonded Si/SiO₂ interface, decreases by more than four orders of magnitude at the mid-gap compared with the peak density observed at the activation energy E _a ≈0.2–0.3 eV. The capture centers are also found in the split-off Si layer of the fabricated SOI structures. Their activation energy at room temperature is E _a =0.53 eV, the capture cross section is 10^?19 cm², and the concentration is (0.7–1.7)×10¹³ cm^?3. It is assumed that these capture centers are related to deep bulk levels induced by electrically active impurities (defects) in the split-off Si layer close to the Si/SiO₂ interface.     

States of antimony and tin atoms in lead chalcogenides

It is shown by Mössbauer spectroscopy of the ¹¹⁹Sb(^119m Sn) isotope that impurity antimony atoms in PbS, PbSe, and PbTe lattices are distributed between cation and anion sublattices. In n-type samples, the greatest part of antimony is located in the anion sublattice; in hole ones, in the cation sublattice. The tin atoms formed as a result of radioactive decay of ¹¹⁹Sb (antisite state) are electrically inactive in the anion sub-lattice of PbS and PbSe, while, in the cation sublattice, they form donor U ^? centers. Electron exchange between the neutral and doubly ionized tin U ^? centers via the allowed band states is observed. The tin atoms formed after radioactive decay of ¹¹⁹Sb are electrically inactive in the anion and cation sublattices of PbTe.     

A small-molecule organic semiconductor

The electrical conductivity and optical properties of bis-diethylaminokumarin have been investigated. The electrical conductivity of the compound exhibited three-dimensional hopping conduction in the temperature range 295–321 K. The compound shows a typical semiconductor property, and its semiconducting property results from delocalization of the π-electrons in the structure. To determine the optical band gap of the compound, an optical absorption study was made in the wavelength range 250–600 nm. The optical study revealed that the optical transition is the allowed indirect one. The electronic parameters, such as the electrical conductivity at room temperature σ₂₅, activation energy E, and optical band gap E_g of the compound are 1.46×10^?5 S/cm, 0.42 eV, and 2.46 eV, respectively. These values are in agreement with electronic parameters of organic semiconductors.     

Specific features of conductivity of Cd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>x</Subscript>Te and Cd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>x</Subscript>Te single crystals

The electrical characteristics of p-type Cd_1?xZn_xTe (x=0.05) and Cd_1?xMn_xTe (x=0.04) single crystals with a resistivity of 10³–10¹⁰ Ω cm at 300 K are studied. The conductivity and its variation with temperature are interpreted on the basis of statistics of electrons and holes in a semiconductor with deep acceptor impurities (defects), with regard to their compensation by donors. The depth of acceptor levels and the degree of their compensation are determined. The problems of attaining near intrinsic conductivity close to intrinsic are discussed.     

Radiation-induced bistable centers with deep levels in silicon <Emphasis Type="Italic">n</Emphasis> <Superscript>+</Superscript>–<Emphasis Type="Italic">p</Emphasis> structures

The method of deep level transient spectroscopy is used to study electrically active defects in p-type silicon crystals irradiated with MeV electrons and α particles. A new radiation-induced defect with the properties of bistable centers is determined and studied. After keeping the irradiated samples at room temperature for a long time or after their short-time annealing at T ～ 370 K, this defect does not display any electrical activity in p-type silicon. However, as a result of the subsequent injection of minority charge carriers, this center transforms into the metastable configuration with deep levels located at E_V + 0.45 and E_V + 0.54 eV. The reverse transition to the main configuration occurs in the temperature range of 50–100°C and is characterized by the activation energy ～1.25 eV and a frequency factor of ～5 × 10¹⁵ s^–1. The determined defect is thermally stable at temperatures as high as T ～ 450 K. It is assumed that this defect can either be a complex of an intrinsic interstitial silicon atom with an interstitial carbon atom or a complex consisting of an intrinsic interstitial silicon atom with an interstitial boron atom.     

Study of the electrical properties of Cd<Subscript>x</Subscript>Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te

On the basis of the temperature and field dependences of the Hall coefficient R _H , it was found that samples with a low electron density are, as a rule, compensated, and the degree of compensation changes upon thermal conversion of the conductivity of the sample to p type. For n-Cd_xHg_1?xTe, the ionization energy of the donor level was found from the temperature dependences of resistivity ρ(T): E _d =24–32 meV. For the same samples, after their thermal conversion to p type, the ionization energies of acceptors, which are related to doubly charged vacancies V _Hg ⁺⁺ , were determined: E _a =32 and 48 meV. In addition, a deep level E _t , related to an unknown amphoteric impurity, was found (E _t ?E _v ≈0.7E _g ).     

The variation in activity of recombination centers in silicon <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis> structures under the conditions of acoustic loading

Using the method of differential coefficients of current-voltage characteristics, deep levels in the Cz-Si p-n structures are studied under the ultrasonic loading conditions (longitudinal waves of a frequency of 4–26 MHz and intensity as high as 0.6 W/cm²). The levels with thermal activation energy of 0.44, 0.40, 0.37, 0.48, and 0.46 eV are revealed. It is assumed that these levels are associated with the E center, bistable B_SO_2i complex, and interstitial atoms captured by dislocation loops, respectively. It is established that ultrasound induces an increase in the contribution to the recombination processes of shallower levels and a decrease in activation energy of defects. The possibility of acoustoinduced reversible reconstruction of the configuration of the B_SO_2i complex is analyzed.     

The effect of thickness fluctuations on the static electrical conductivity of a semiconductor quantum wire

Expressions for the relaxation time, electron mobility, and static electrical conductivity along a semiconductor quantum wire are derived in relation to a random field of Gaussian fluctuations in the wire’s thickness. In the case of nondegenerate statistics for charge carriers at relatively low temperatures (T), electron mobility is given by u _n ∝ T^1/2. In the limiting case of a strong magnetic field H directed along the wire, the factor H^?1/2 appears in the mobility expression. It is shown that the considered mechanism of charge-carrier relaxation is important for the electrical conductivity of a fairly thin and pure quantum wire at low temperatures.     

Features of structural,electron-transport,and magnetic properties of heavily doped <Emphasis Type="Italic">n</Emphasis>-ZrNiSn semiconductor: Fe acceptor impurity

Structural, energy, electron-transport, and magnetic characteristics of the n-ZrNiSn intermetallic semiconductor heavily doped with Fe (the concentration N _Fe ≈ 9.7 × 10¹⁹?3.8 × 10²¹ cm^?3) in the temperature range T = 80–380 K are investigated. It is shown that the Fe atoms simultaneously occupy crystallographic sites of Zr and Ni atoms in different relations being the defects of the donor and acceptor nature, respectively. The relation between the impurity concentration, the amplitude of large-scale fluctuation, and the degree of filling of the potential well of the small-scale fluctuation (fine structure) by charge carriers is established. The results are discussed within the context of the Shklovskii-Efros model of a heavily doped and compensated semiconductor.     

Influence of charged defects on detection of electron spin resonance in vitreous chalcogenide semiconductors

A relationship between the concentrations of induced spins and native U^? centers is established on the basis of taking electronic processes accompanying band-to-band excitation into account.     

Electronic Processes in CdIn<Subscript>2</Subscript>Te<Subscript>4</Subscript> Crystals

The results of investigations of electrical, optical, and photoelectric properties of CdIn₂Te⁴ crystals, which were grown by the Bridgman method are presented. It is shown that electrical conductivity is determined mainly by electrons with the effective mass m_n = 0.44m₀ and the mobility 120–140 cm²/(V s), which weakly depends on temperature. CdIn₂Te₄ behaves as a partially compensated semiconductor with the donor-center ionization energy E_d = 0.38 eV and the compensation level K = N_a/N_d = 0.36. The absorption-coefficient spectra at the energy hν < E_g = 1.27 eV are subject to the Urbach rule with a typical energy of 18–25 meV. The photoconductivity depends on the sample thickness. The diffusion length, the charge-carrier lifetime, and the surface-recombination rate are determined from the photoconductivity spectra.     

Role of Si-doped Al<Subscript>0.3</Subscript>Ga<Subscript>0.7</Subscript>As layers in the high-frequency conductivity of GaAs/Al<Subscript>0.3</Subscript>Ga<Subscript>0.7</Subscript>As heterostructures under conditions of the quantum hall effect

The complex high-frequency conductivity of GaAs/Al_0.3Ga_0.7As heterostructures that are δ-doped and modulation-doped with silicon was investigated by acoustic methods under conditions of the integer quantum Hall effect. Both the real (σ₁) and imaginary (σ₂) parts of the complex conductivity σ(ω, H)=σ_i?iσ₂ were determined from the dependences of the absorption and velocity of surface acoustic waves on magnetic field. It is shown that, in the heterostructures with electron density n_s=(1.3–7)×10¹¹ cm^?2 and mobility μ=(1–2)×10⁵ cm²/(V s), the high-frequency conductivity near the centers of the Hall plateau is due to electron hopping between localized states. It is established that, with filling numbers 2 and 4, the conductivity of the Al_0.3Ga_0.7As:Si layer efficiently shunts the high-frequency hopping conductivity of the two-dimensional interface layer. A method of separating the contributions of the interface and Al_0.3Ga_0.7As:Si layers to the hopping conductivity σ(ω, H) is developed. The localization length of electrons in the interface layer is determined on the basis of the nearest neighbor hopping model. It is shown that, near the centers of the Hall plateau, both σ(ω, H) and n_s depend on the cooling rate of a GaAs/Al_0.3Ga_0.7As sample. As a result, the sample “remembers” the cooling conditions. Infrared light and static strain also change both σ(ω, H) and n_s. We attribute this behavior to the presence of two-electron defects (so-called DX^? centers) in the Al_0.3Ga_0.7As:Si layer.     

Characterization of <Emphasis Type="Italic">n</Emphasis>-Type and <Emphasis Type="Italic">p</Emphasis>-Type Long-Wave InAs/InAsSb Superlattices

The influence of dopant concentration on both in-plane mobility and minority carrier lifetime in long-wave infrared InAs/InAsSb superlattices (SLs) was investigated. Unintentially doped (n-type) and various concentrations of Be-doped (p-type) SLs were characterized using variable-field Hall and photoconductive decay techniques. Minority carrier lifetimes in p-type InAs/InAsSb SLs are observed to decrease with increasing carrier concentration, with the longest lifetime at 77 K determined to be 437 ns, corresponding to a measured carrier concentration of p ₀ = 4.1 × 10¹⁵ cm^?3. Variable-field Hall technique enabled the extraction of in-plane hole, electron, and surface electron transport properties as a function of temperature. In-plane hole mobility is not observed to change with doping level and increases with reducing temperature, reaching a maximum at the lowest temperature measured of 30 K. An activation energy of the Be-dopant is determined to be 3.5 meV from Arrhenius analysis of hole concentration. Minority carrier electrons populations are suppressed at the highest Be-doping levels, but mobility and concentration values are resolved in lower-doped samples. An average surface electron conductivity of 3.54 × 10^?4 S at 30 K is determined from the analysis of p-type samples. Effects of passivation treatments on surface conductivity will be presented.