A study of recombination centers in irradiated <Emphasis Type="Italic">p</Emphasis>-Si crystals

p-Si samples irradiated with 8-Mev electrons are studied. It is suggested that the multicomponent V₃+O or V₂+O₂ complexes are not recombination centers on the basis of an analysis of the dependences of the minority-carrier lifetime τ, the resistivity ρ, the concentration p, and the Hall mobility μ_H on the temperature of isochronous annealing T_ann. Deep donors with energy levels at ΔE_i=E_v+0.40 eV and the V₃+O₃ and the V₃+O₂ complexes affect the values of μ_H and τ. The curves of isochronous annealing are used to determine the annealing-activation energies E_ann for defects such as K centers, interstitial carbon atoms C_i, the V+B and V₂+O₂ complexes, divacancies V₂, and defects with a level at ΔE_i=E_v+0.20 eV. These energies were found to be equal to E_ann=0.9, 0.25, 1.6, 2, 1.54, and 2.33 eV, respectively.     

The influence of the energy of photoexcitation in the course of electron irradiation on defect formation in <Emphasis Type="Italic">n</Emphasis>-Si crystals

Effect of illumination of n-Si crystals in the course of irradiation with electrons on the nature of radiation defects is studied. The samples irradiated with 2-MeV electrons were subjected to isochronous annealing in the temperature range from 200 to 600°C. After each 20-min cycle of annealing, the electron concentration was measured by the Hall method in the temperature range 77–300 K. It is shown that, if the E centers are excited during irradiation with photons with the energy hν = 0.44 eV (the wavelength λ = 2.8 μm), divacancy phosphorus-containing defects of the PV ₂ type are formed in the n-Si crystals, which leads to an increase in the radiation resistance of the crystals under study. If negative vacancies V ^? are excited with photons with the energy hν = 0.28 eV (λ = 4.4 μm), the total number of radiation defects increases by a factor of 1.2.     

Migration energy of vacancies in <Emphasis Type="Italic">p</Emphasis>-type silicon crystals

p-Si:B samples were irradiated with 8-MeV electrons. The values of the activation energy of annealing for K centers and for (V + B) complexes obtained from the curves of isochronous annealing of these centers are found to be equal to 0.915 and 1.6 eV, respectively. The volumetric measurements of photovoltage over the irradiated region make it possible to estimate the values of the migration energy of vacancies. The migration energy is found to be \(E_{V^{ + + } }^M \approx 0.6 eV\) for positively charged vacancies and \(E_{V^0 }^M \approx 0.345 eV\) for neutral vacancies.     

Electrical properties of Zinc-Tin diarsenide (ZnSnAs<Subscript>2</Subscript>) irradiated with H<Superscript>+</Superscript> ions

The results of studying the electrical properties and isochronous annealing of p-ZnSnAs₂ irradiated with H⁺ ions (energy E = 5 MeV, dose D = 2 × 10¹⁶ cm^?2) are reported. The limiting electrical characteristics of irradiated material (the Hall coefficient R _H (D)_lim ≈ ?4 × 10³ cm³ C^?1, conductivity σ (D)_lim ≈ 2.9 × 10^?2 Ω^?1 cm^?1, and the Fermi level position F _lim ≈ 0.58 eV above the valence-band top at 300 K) are determined. The energy position of the “neutral” point for the ZnSnAs₂ compound is calculated.     

Dependence of dicarbon annealing temperature in <Emphasis Type="Italic">n</Emphasis>-Si on oxygen concentration in the crystal

The role of oxygen in the mechanism of dissociation of the dicarbon complex in n-Si into components is considered. It is assumed that released interstitial carbon atoms C_i migrate through the crystal and react with both substitutional carbon C_s and interstitial oxygen with the resulting formation of complexes C_iC_s and C_iO_i, respectively. The solution of a system of equations describing the formation of interstitial carbon atoms in the course of annealing of dicarbon show that the rate constant for the reaction of annealing of the C_iC_s complex (the G center) depends on the oxygen concentration. This dependence is treated as the dependence of the activation energy for annealing of a C_iC_s complex and, consequently, the dissociation energy of this complex on oxygen concentration. A more accurate value of dissociation energy for the G center was determined as 1.08±0.03 eV.     

Detection of hydrogen impurity in silicon radiation detectors

The behavior of silicon particle detectors irradiated with 2.5-MeV electrons during subsequent annealing is studied. Annealing at 100–250°C was found to result in the formation of two types of traps with the levels E _c ?0.32 eV and E_v+0.29 eV. Increasing the annealing temperature to 300°C makes both traps disappear. On the basis of data obtained, it was concluded that these traps are related to hydrogen-containing complexes. The presence of hydrogen in a crystal results in a decrease in the annealing temperature for vacancy-oxygen (VO) complexes and complexes consisting of carbon and oxygen interstitials (C_iO_i). The reason for this phenomenon is the passivation of these complexes by hydrogen, which results in the formation of electrically active VOH centers {with the level E _c ?0.32 eV} in an intermediate stage of this process. It is assumed that hydrogen penetrates the structures under investigation in one of the stages of their fabrication.     

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.     

Special features of annealing of radiation defects in irradiated <Emphasis Type="Italic">p</Emphasis>-Si crystals

p-Si single crystals grown by the Czochralski method were studied; the hole concentration in these crystals was p = 6 × 10¹³ cm^?3. The samples were irradiated with 8-MeV electrons at 300 K and were then annealed isochronously in the temperature range T _ann = 100–500°C. The studies were carried out using the Hall method in the temperature range of 77–300 K. It is shown that annealing of divacancies occurs via their transformation into the B _s V ₂ complexes. This complex introduces the energy level located at E _v + 0.22 eV into the band gap and is annealed out in the temperature range of 360–440°C. It is assumed that defects with the level E _v + 0.2 eV that anneal out in the temperature range T _ann = 340–450°C are multicomponent complexes and contain the atoms of the doping and background impurities.     

Low-temperature instabilities of the electrical properties of Cd<Subscript>0.96</Subscript>Zn<Subscript>0.04</Subscript>Te:Cl semi-insulating crystals

The electrical properties in the temperature range 295–430 K and low-temperature (4.2 K) photoluminescence of Cd_1?xZn_xTe:Cl semi-insulating crystals grown from melts with a variable impurity content (C _Cl ⁰ = 5 × 10¹⁷–1 × 10¹⁹ cm^?3) are investigated. Nonequilibrium processes leading to a decrease in carrier concentration are observed in all the samples at low temperatures (T = 330–385 K). These changes are reversible. The activation energy of these processes E _a is found to be 0.88 eV. As with semi-insulating CdTe:Cl, the observed phenomena can be explained by a change in the charge state of background copper atoms: Cu_Cd ? Cu_i. The introduction of Zn changes the ratio of the concentrations of shallow-level donors Cu_i and Cl_Te from their levels in the initial material.     

Carrier Transport Mechanism and Band Offsets at the Interface of ZnS/<Emphasis Type="Italic">n</Emphasis>-Si (111) Heterojunctions Fabricated by Vacuum Thermal Evaporation

The electrical properties and band offset of ZnS/n-Si(111) heterojunctions with and without annealing were analyzed. The result showed that the rectifying characteristics of ZnS/n-Si(111) heterojunctions became better and the leakage current increased after annealing. This phenomenon is mostly due to the volatilization of S atoms of ZnS films and leads to defect levels appearing at the interface of the ZnS/n-Si(111) hetrojunctions. The valence band offset (ΔE _V) of the ZnS/n-Si(111) heterojunctions can be calculated to be ?0.7 ± 0.15 eV by means of photoelectron spectroscopy, indicating that the band offsets of ZnS/n-Si(111) heterojunctions show a type-II band alignment.     

Study of photocapacitance in diodes fabricated from silicon doped with vanadium

The levels of vanadium in the band gap of n-and p-Si were determined using photocapacitance measurements. It is shown that vanadium introduces levels only in the upper half of the band gap of n-Si; these levels have ionization energies of about E _c ?0.21 eV, E _c ?0.32 eV, and E _c ?0.52 eV. By contrast, V levels are located both in the upper and lower halves of the p-Si band gap: E _c ?0.26 eV, E _v +0.52 eV, E _v +0.42 eV, and E _v +0.31 eV. It is ascertained that the photoionization cross sections of all vanadium levels are larger for electrons than for holes. It is shown that the concentration of electrically active vanadium centers in n-and p-Si depends on both the concentration of shallow-level impurities and the time of vanadium diffusion into Si.     

Special features of radiation-defect annealing in silicon <Emphasis Type="Italic">p-n</Emphasis> structures: The role of Fe impurity atoms

Deep-level transient spectroscopy is used to study the formation of complexes that consist of a radiation defect and a residual impurity atom in silicon. It is established that heat treatment of the diffused Si p⁺-n junctions irradiated with fast electrons lead to the activation of a residual Fe impurity and the formation of the FeVO (E_0.36 trap) and FeV₂ (H_0.18 trap) complexes. The formation of these traps is accompanied by the early (100–175°C) stage of annealing of the main vacancy-related radiation defects: the A centers (VO) and divacancies (V₂). The observed complexes are electrically active and introduce new electron (E_0.36: E _t ^e =E _c -0.365 eV, σ _n =6.8×10^?15 cm²) and hole (H_0.18: E _t ^h =E _v +0.184 eV, σ _p =3.0×10^?15 cm²) levels into the silicon band gap and have a high thermal stability. It is believed that the complex FeVO corresponds to the previously observed and unidentified defects that have an ionization energy of E _t ^e =E _c ?(0.34–0.37) eV and appear as a result of heat treatment of irradiated diffused Si p⁺-n junctions.     

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.     

Formation and annealing of radiation defects in tin-doped <Emphasis Type="Italic">p</Emphasis>-type germanium crystals

The effect of tin on the formation and annealing of radiation defects in p-type germanium crystals irradiated with 6-MeV electrons at a temperature of 80 K is studied. It is shown that acceptor complexes SnV with a hole ionization enthalpy of 0.16 eV are dominant in irradiated Ge:(Sn, Ga) crystals after their heating to a temperature of 300 K. These complexes disappeared as a result of the annealing of irradiated crystals in the temperature range 30–75°C. Annealing of irradiated crystals at temperatures in the range 110–150°C brings about the formation of deep-level centers with a donor level at E _v + 0.29 eV; this center is presumably related to a complex consisting of a tin atom and an interstitial gallium atom.     

Structural and Electrical Properties of Ag/<Emphasis Type="Italic">n</Emphasis>-TiO<Subscript>2</Subscript>/<Emphasis Type="Italic">p</Emphasis>-Si/Al Heterostructure Fabricated by Pulsed Laser Deposition Technique

We have investigated the structural and electrical characteristics of the Ag/n-TiO₂/p-Si/Al heterostructure. Thin films of pure TiO₂ were deposited on p-type silicon (100) by optimized pulsed laser ablation with a KrF-excimer laser in an oxygen-controlled environment. X-ray diffraction analysis showed the formation of crystalline TiO₂ film having a tetragonal texture with a strong (210) plane as the preferred direction. High purity aluminium and silver metals were deposited to obtain ohmic contacts on p-Si and n-TiO₂, respectively. The current–voltage (I–V) characteristics of the fabricated heterostructure were studied by using thermionic emission diffusion mechanism over the temperature range of 80–300 K. Parameters such as barrier height and ideality factor were derived from the measured I–V data of the heterostructure. The detailed analysis of I–V measurements revealed good rectifying behavior in the inhomogeneous Ag/n-TiO₂/p-Si(100)/Al heterostructure. The variations of barrier height and ideality factor with temperature and the non-linearity of the activation energy plot confirmed that barrier heights at the interface follow Gaussian distributions. The value of Richardson’s constant was found to be 6.73 × 10⁵ Am^?2 K^?2, which is of the order of the theoretical value 3.2 × 10⁵ Am^?2 K^?2. The capacitance–voltage (C–V) measurements of the heterostructure were investigated as a function of temperature. The frequency dependence (Mott–Schottky plot) of the C–V characteristics was also studied. These measurements indicate the occurrence of a built-in barrier and impurity concentration in TiO₂ film. The optical studies were also performed using a UV–Vis spectrophotometer. The optical band gap energy of TiO₂ films was found to be 3.60 eV.     

Electrical properties of ZnSiAs<Subscript>2</Subscript> irradiated with protons

The electrical properties of p-ZnSiAs₂ irradiated with protons (energy E = 5 MeV, dose D ≤ 2 × 10¹⁷ cm^?2) are studied. Experimental data and results of calculations are used to estimate the limiting position of the Fermi level in the band gap of the irradiated material (at the midgap E _g/2). The thermal stability of radiation defects in the temperature range from 20 to 610°C was analyzed.     

On the photoconductivity of TlInSe<Subscript>2</Subscript>

The current–voltage (I–V) and photocurrent–light intensity (I _pc –Φ) characteristics and the photoconductivity relaxation kinetics of TlInSe₂ single crystals are investigated. Anomalously long relaxation times (τ ≈ 10³ s) and some other specific features of the photoconductivity are observed, which are explained within the barrier theory of inhomogeneous semiconductors. The heights of the drift and recombination barriers are found to be, respectively, E _dr ≈ 0.1 eV and E _r ≈ 0.45 eV.     

Structurally complex two-hole and two-electron slow traps with bikinetic properties in <Emphasis Type="Italic">p</Emphasis>-ZnTe and <Emphasis Type="Italic">n</Emphasis>-ZnS crystals

Thermal-activation and photoactivation methods were used to ascertain the existence of two-hole traps in p-ZnTe crystals and two-electron traps in n-ZnS. It was found that these traps have a large number of energy states that are grouped in two series of levels: E_V+(0.46–0.66) eV and E_V+(0.06–0.26) eV in p-ZnTe and E_C?(0.6–0.65) eV and E_C?(0.14–0.18) eV in n-ZnS. Both the hole and the electron traps belong to the class of slow traps with bikinetic properties. These traps feature normal kinetic properties in the state with a single trapped charge carrier and feature anomalous kinetic properties in the state with two charge carriers. Multiple-parameter models allowing for a relation of traps in p-ZnTe and n-ZnS to the vacancy-impurity pairs distributed according to their interatomic distances and localized in the region of microinhomogeneities with collective electric fields that repel the majority charge carriers are suggested. The main special features of behavior of electron and hole traps are explained consistently using the above models.     

Dielectric Relaxation in Thin Layers of the Ge<Subscript>28.5</Subscript>Pb<Subscript>15</Subscript>S<Subscript>56.5</Subscript> Glassy System

The results of studying dielectric relaxation processes in the Ge_28.5Pb₁₅S_56.5 glassy system are presented. The existence of the non-Debye relaxation process caused by the distribution of relaxors over the relaxation time according to the Cole–Cole model is revealed. The energy and structural parameters are calculated: the activation energy E_p = 0.40 eV and the molecular dipole moment μ = 1.08 D. The detected features are explained within the model according to which the chalcogenide-glass structure is a set of dipoles formed by charged defects such as D⁺ and D^–.     

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.