Search

The kinetics of the formation of radiation-induced defects in silicon and silicon carbide as a function of the absorbed energy is analyzed. The dependence of the concentration of conduction electrons n-Si and n-SiC on the irradiation dose is studied experimentally under conditions of irradiation with electrons with an energy of 0.9 MeV and protons with an energy of 15 MeV. The advantages and disadvantages of using the integral flux (fluence) and absorbed energy as kinetic parameters are discussed. It is established in the performed studies that the visual representation of the kinetics of radiation-induced defect formation as a function of the fluence of irradiating particles is clearer for tabulating the requirements imposed to equipment stability under suitable conditions. To study the physical processes underlying the formation of radiation-induced defects in semiconductors, it is more convenient to use the dependences of the effects observed under radiation exposure as functions of the absorbed energy.

The processes of the compensation of n-type conductivity in germanium irradiated with 15-MeV protons are investigated. Irradiation results in a considerable reduction in the density of shallow donor states of Group-V atoms. The rate of removal of shallow donor states due to the interaction between impurity atoms and radiation-induced intrinsic point defects is ~215 cm–1. The majority of secondary defects produced under proton irradiation are electrically neutral in an n-type material. Radiation-induced acceptors are of little importance in this case. Numerical modeling is performed, and the distribution of the energy transferred to recoil atoms is obtained. Two energy intervals are considered in the analysis of distribution histograms. At low energies, individual Frenkel pairs with closely spaced components are produced. The energy of recoil atoms in the second energy region is sufficient to induce a displacement cascade. Nanoscopic regions with high densities of intrinsic point defects and their complexes with dopant atoms are formed in such cascades. A model of the generation of intrinsic defects in germanium under proton irradiation is discussed.

It has been shown that the interaction of 1 MeV protons at doses of (0.5–2) × 1014 cm–2 with transistor structures having a 2D AlGaN/GaN channel (AlGaN/GaN HEMTs) is accompanied not only by the generation of point defects, but also by the formation of local regions with a disordered nanomaterial. The degree of disorder of the nanomaterial was evaluated by multifractal analysis methods. An increase in the degree of disorder of the nanomaterial, manifested the most clearly at a proton dose of 2 × 1014 cm–2, leads to several-fold changes in the mobility and electron density in the 2D channel of HEMT structures. In this case, the transistors show a decrease in the source–drain current and an order-of-magnitude increase in the gate leakage current. In HEMT structures having an enhanced disorder of the nanomaterial prior to exposure to protons, proton irradiation results in suppression of the 2D conductivity in the channel and failure of the transistors, even at a dose of 1 × 1014 cm–2.

Processes of radiation defect formation and conductivity compensation in silicon and silicon carbide irradiated with 0.9 MeV electrons are considered in comparison with the electron irradiation at higher energies. The experimental values of the carrier removal rate at the electron energy of 0.9 MeV are nearly an order of magnitude smaller than the similar values of the parameter for higher energy electrons (6–9 MeV). At the same time, the formation cross-section of primary radiation defects (Frenkel pairs, FPs) is nearly energy-independent in this range. It is assumed that these differences are due to the influence exerted by the energy of primary knocked-on atoms (PKAs). As the PKA energy increases, the average distance between the genetically related FPs grows and, as a consequence, the fraction of FPs unrecombined under irradiation becomes larger. The FP recombination radius is estimated (∼1.1 nm), which makes it possible to ascertain the charge state of the recombining components. Second, the increase in the PKA energy enables formation of new, more complex secondary radiation defects. At electron energies exceeding 15 MeV, the average PKA energies are closer to the values obtained under irradiation with 1 MeV protons, compared with an electron irradiation at the same energy. As for the radiation-induced defect formation, the irradiation of silicon with MeV protons can be, in principle, regarded as a superposition of the irradiation with 1 MeV electrons and that with silicon ions having energy of ∼1 keV, with the “source” of silicon ions generating these ions uniformly across the sample thickness.

Electrical properties of defects formed in n-Si(FZ) following 8 and 15 MeV proton irradiation are investigated by Hall effect measurements over the wide temperature range of T ≈ 25 to 300 K. Close attention is paid to the damaging factor of proton irradiation, leaving aside passivation effects by hydrogen. The concept of defect production and annealing processes being accepted in the literature so far needs to be reconsidered. Contrary to expectations the dominant impurity-related defects produced by MeV protons turn out to be electrically neutral in n-type material. Surprisingly, radiation acceptors appear to play a minor role. Annealing studies of irradiated samples of such complex defects as a divacancy tied to a phosphorus atom and a vacancy tied to two phosphorus atoms. The latter defect features high thermal stability. Identification of the dominant neutral donors, however, remains unclear and will require further, more detailed, studies. The electric properties of the material after proton irradiation can be completely restored at T = 800°C.

The first experimental results demonstrating that the carrier mobility in the AlGaN/GaN 2D channel of transistor structures (AlGaN/GaN-HEMT) is correlated with the manner in which the nanomaterial is organized and also with the operation reliability of transistor parameters are presented. It is shown that improving the nature of organization of the nanomaterials in AlGaN/GaN-HEMT structures, evaluated by the multifractal parameter characterizing the extent to which a nanomaterial is disordered (local symmetry breaking) is accompanied by a significant, several-fold increase in the electron mobility in the 2D channel and in the reliability of parameters of transistors fabricated from these structures.

We applied positron annihilation lifetime spectroscopy to study the proton-irradiation-induced defects in germanium and its annealing behavior. The n-doped Ge ([As] = 9 × 1017 cm−3) samples were irradiated at room temperature with a proton energy of 15 MeV at a dose of 1015 cm−2. We distinguished a complex containing a vacancy and arsenic atoms. In addition, we observed shallow positron traps, which are ascribed to the impurities in a Ge lattice crystal. Isochronal annealing experiments were carried out in the temperature interval 300–820 K. Temperature-dependent positron lifetime measurements were performed after each annealing step. During isochronal annealing of the proton-irradiated Ge, a vacancy–As complex was found to dissociate to its constituents and the single monovacancies eventually anneal out. Two annealing stages were observed: the first, at ∼450 K, was attributed to the dissociation of complexes and the second annealing stage, at 650 K, was assigned to annealing of vacancies. Shallow positron traps anneal in the temperature range 540–660 K.

The present experiments using fast electron and gamma-irradiation are aimed at checking the model of defect formation in oxygen-lean n-Si(FZ) in a quantitative way. Electrical measurements are taken over a wide temperature range of 20 to 300 K. Analysis of equations of charge balance making use of the statistics of charge carriers in non-degenerate semiconductors demonstrates that group-V impurity atoms strongly interact with intrinsic point defects. As a result, the concentration of shallow donor states is markedly decreased. This loss of shallow donors, −δND, is accompanied with an increase in the concentration of radiation-produced deep acceptors, +δNArad, being equal in magnitude but opposite in sign. Such behavior correlates quantitatively with the formation model of donor-vacancy pairs put forward earlier by Watkins and Corbett, what has been proved on the basis of electrical data for the first time. The formation kinetics of these complexes is discussed. Defects of interstitial type in irradiated material appear to be electrically neutral in n-Si. However, their production in the course of electron- and gamma-irradiation is believed to be responsible for drastic changes in the mobility of charge carriers at cryogenic temperatures.

Effects of irradiation with 0.9 MeV electrons as well as 8 and 15 MeV protons on moderately doped n-Si grown by the floating zone (FZ) technique and n-SiC (4H) grown by chemical vapor deposition are studied in a comparative way. It has been established that the dominant radiation-produced defects with involvement of V group impurities differ dramatically in electron- and proton-irradiated n-Si (FZ), in spite of the opinion on their similarity widespread in literature. This dissimilarity in defect structures is attributed to a marked difference in distributions of primary radiation defects for the both kinds of irradiation. In contrast, DLTS spectra taken on electron- and proton-irradiated n-SiC (4H) appear to be similar. However, there are very much pronounced differences in the formation rates of radiation-produced defects. Despite a larger production rate of Frenkel pairs in SiC as compared to that in Si, the removal rates of charge carriers in n-SiC (4H) were found to be considerably smaller than those in n-Si (FZ) for the both electron and proton irradiation. Comparison between defect production rates in the both materials under electron and proton irradiation is drawn.

The dose dependences of the effect of deep semiconductor-conductivity compensation under bombardment with electrons is studied. It is discovered that the linear dependences are characteristic for SiC and GaAs, and the strictly nonlinear dependence is typical of Si. Calculations are carried out, and it is shown that the character of the dose dependence is determined by the compensation mechanism. A model explaining the difference between the characters of the dependences for different semiconductors is proposed.

Rates of carrier removal from the conduction band in n-type FZ-Si and 4H-SiC irradiated with 8- and 15-MeV protons at room temperature are discussed. Calculated rates of formation of primary radiation defects (Frenkel pairs) in these materials are presented and compared with the corresponding experimental values. Protons create defects in collision cascades involving recoil atoms formed in the crystal lattice itself. The results are compared with similar data previously obtained in irradiation of n-type FZ-Si and 4H-SiC with 900-keV electrons, in which case isolated so-called close Frenkel pairs are absolutely dominant among primary radiation defects. It has been found that the E-center model adequately describing the decrease in the electrical conductivity of n-FZ-Si upon electron irradiation is inapplicable to interpretation of experimental data for proton-irradiated materials. It is suggested that a pronounced annealing of “simple” radiation defects of the type of close Frenkel pairs occurs during irradiation at room temperature.

Electrically active defects induced in oxygen-rich Ge:Sb crystals by irradiation with MeV electrons at 80 or 300 K have been studied by means of capacitance transient techniques. Transformations of the defects upon post-irradiation isochronal anneals have also been investigated. It is argued that a radiation-induced electron trap with an energy level at about 110 meV below the conduction band edge (E110) can be associated with electron emission from an energy level of the Ge self-interstitial (IGe). The E110 trap is eliminated in the temperature range 150–200 K upon 15 min isochronal annealing. No other traps in the upper half of the gap emerge simultaneously with the disappearance of the E110 trap. It is argued that Ge self-interstitials become mobile at temperatures higher than 150 K and in oxygen-rich Ge interact with interstitial oxygen atoms (Oi). The resulting IGeOi complexes do not have energy levels in the upper half of the Ge gap. Diffusion and interaction of the IGeOi defects with interstitial oxygen atoms at T>50 °C result in the formation of IGeO2i complexes. In the most stable configuration the IGeO2i complex has orthorhombic (C2v) symmetry.

The emission of the high-momentum annihilation radiation from the subvalent ion core shells and electron density around a positron localized at a vacancy-group-V-impurity atom complexes produced in oxygen-lean Ge doped with P, As, Sb, and Bi by irradiation with 60Co gamma-rays at room temperature have been investigated with the help of the angular correlation of annihilation radiation (ACAR) before and after n→p conversion. The probability of positron annihilation in the subvalent shells of atoms incorporated in dominant radiation centers was found to be dependent on the ratio of the ion core radii ri(P5+, As5+)/ri(Ge4+) 1, respectively. In passing from P to As impurity atoms the activation energy ΔEe of electron emission to be detected by DLTS measurements is increased by ~(+0.017 eV) vs. the increase of the electron density parameter to be reconstructed by ACAR data, Δr′s=r′s(As)−r′s(P)≈0.029 a.u. On the contrary, in passing from Sb to Bi impurity atoms, ΔEe value is decreased by ~(−0.028 eV) whereas the electron density parameter rises by Δr′s=r′s(Bi)−r′s(Sb)≈0.04 a.u. After n→p conversion a marked decrease in both the electron density and the number of ion cores around the positron points to the fact that the radiation-produced complexes with group-V-impurity atoms (P, As, Sb, Bi) are of a multi-vacancy character. The deep acceptor states in the forbidden gap (Ev+0.1), (Ev+0.12), (Ev+0.16) eV to be attributed to the P-, As-, Sb-, and Bi-containing multi-vacancy centers, respectively, were found to contribute to lessening the electron density around the trapped positron. It is argued that a close similarity of the As5+ and Ge4+ ion cores results in a small (but marked) augmentation in the electron density around the positron in As-containing multi-vacancy centers after n→p conversion. A trend for inward relaxation of the ion cores is observed in all radiation-produced centers studied.

The production and annealing of oxygen and carbon related defects in electron-irradiated Ge-doped Czochralski silicon have been studied by means of IR spectroscopy. The results demonstrate that the role of Ge changes with increasing Ge content. At low Ge concentrations, much less than 1020 cm−3, Ge atoms act as temporary traps for vacancies preventing their annihilation with self-interstitials. At high Ge concentrations, Ge atoms form clusters which tend to attract vacancies and self-interstitials, enhancing their mutual annihilation. As a result, for low Ge concentrations the production of oxygen-related defects (VO) and carbon-related defects (CiOi, CiOi(SiI), CiCs) tend to increase as a function of Ge content, while for high Ge concentrations tend to decrease. The annealing of the oxygen-related defects VOn (1≤n≤6) is also affected by the Ge presence. The ratio of the VO defects that convert to VO2 is reduced in Ge doped material. However, this ratio increases for the conversions VOn→VOn+1 (3≤n≤5), respectively. The annealing temperature of VO defect and the growth temperature of VO2 defect decrease versus Ge content. On the other hand, the thermal stability of the carbon-related defects was found to be insensitive to the presence of Ge. It was also found that the carbon precipitation process shows some marked differences in irradiated Ge-doped Si, in comparison with the undoped material.

The positron probing of the donor-vacancy (DV) complexes created in the single crystals of n-Ge〈D〉 (D=P, As, Sb, or Bi) by γ -irradiation Co-60 (Tirr.≈315 K) has been carried out by measuring the angular correlation of the annihilation radiation (ACAR). The maximum overlapping of the positron and electron wave functions in the subvalent shells of the ion cores has been determined for [1 1 1] crystallographic direction by normal approximation method. It has been found that this maximum is shifted from the nuclei of DV complexes in passing from the ion cores of atoms of a relatively small “size”, P and As, to more volumetric ion cores, Sb and Bi, respectively. The shift itself is accompanied by the increase of the probability of the high-momentum annihilation process of the trapped positron during its lifetime. This increase correlates well with the augmentation of the entropy of ionization revealed by DLTS (Markevich et al. Phys. Rev. B70 (2004) 235213) for group-V-impurity atom pairs in germanium. Kolmogorov-Chapmen formalism has been used for studying the probability of the high-momentum annihilation of positron trapped by DV complexes. The results obtained suggest that the growth of the configurational entropy in passing from the ion cores of relatively small “size” to more volumetric ones is accompanied by the relaxation of the ion cores inward towards the free volume related to the vacancy in DV complex.

Effects of proton irradiation on the optical and electrical properties of n-InN with charge carrier concentrations of 2 - 5 x 10 18 cm -3 have been investigated. Strong changes in photoluminescence spectra and electrical parameters of irradiated n-InN are discussed. Proton irradiation of n-InN results in the appearance of shallow donors in large concentrations. Comparison with the effects observed on heavily degenerate n-InN after proton irradiation leads to the conclusion that these irradiation-produced donors are native defects, most likely vacancies on the nitrogen sublattice.

Production processes of electrically active defects in degenerate silicon subjected to 2.5 MeV electron irradiation at T = 4.2 K and T = 300 K have been studied. The production rates of primary and secondary defects in irradiated samples are analyzed on the basis of the known properties of radiation-produced defects in Si. It has been demonstrated that a striking difference in the production rates of electrically active defects in n- and p-Si under irradiation at cryogenic temperatures may be related to the different fate of Frenkel pairs in both materials. The production rate of primary defects in degenerate Si was found to be between 1.5 cm−1 and 2 cm−1.

For the first time the positron probing of the vacancy—V-group-atom impurity complexes, which were created by γ-irradiating 60Co (Tirr.≈280 K) in the oxygen-lean n-Ge〈V〉 (V=As, Sb, or Bi), has been conducted systematically both before and after n-p-conversion of material. The one-dimensional angular correlation of the annihilation radiation (ACAR) has been registered for crystallographic directions [1 1 1], [1 1 0], and [1 0 0]. The concentration of defects in the same samples was determined from the temperature dependencies of the carrier density and mobility obtained over the range of 4.2–300 K. It was found that (i) the trapping cross section of positrons by the radiation complexes is over the range of (0.7–4.3)×10−15 cm2, and (ii) the size of V-group-atom situated in nearest environment of the positron plays crucial role in generating elementally specific emission of the annihilation γ-quanta. The positron-sensitive vacancy—V-group-atom impurity complexes, or E centres, are formed under γ-irradiation at room temperature in oxygen-lean n-Ge〈V〉 (V=As, Sb, or Bi); this process is accompanied by removing free electrons and at higher doses of irradiation the n-p-conversion occurs. Deeply converted material of p-type contains acceptor centres whose energy levels depending on V-group-atom size are over the range of Ev+(0.1–0.16) eV. The positron annihilation data are interpreted in terms of successive trapping of vacancies by the E centres to be formed, in particular, before n-p-conversion of γ-irradiated material.

Electrically active defects induced by irradiation with MeV electrons in oxygen-rich n-type Ge crystals have been studied by means of capacitance transient techniques. Transformation of the defects upon post-irradiation isochronal and isothermal anneals has also been investigated. It is argued that radiation-induced defects with energy levels at 62 (E62) and 80 meV (E80) below the conduction band edge are associated with complexes of Ge self-interstitials with oxygen-related defects. These complexes are formed upon annealing of electron-irradiated samples at T>50 °C and anneal out at temperatures higher than 140 °C. The activation energy of formation of the dominant E62 defect has been found to be 0.80 eV.

Using photoluminescence and transmission measurements, we have studied the optical properties of indium nitride powder and thin films grown by molecular beam epitaxy. The bandgap for InN powder with electron concentration ∼ 4·1019 cm−3 was 0.94 eV, and for InN films with electron concentrations ∼1018 cm−3 it was 0.7 eV. We have established that when the electron concentration is increased to 8·1019 cm−3, the bandgap of InN increases to 1.0 eV. The change in the bandgap as a function of the concentration is due to the appearance of the Burstein-Moss effect.

Isochronal anneals were performed in Cz-Si samples of high and low carbon concentrations, from room temperature up to 1200 °C. We report infrared studies on the thermal evolution of various bands of oxygen precipitates formed in the course of the annealing process. The effect of carbon on their spectral behavior is examined. It was observed that in the carbon-rich material the oxygen impurity appears to anneal out at a lower temperature than in the carbon-lean material, in agreement with earlier reports that carbon enhances the oxygen precipitation process in Si. In relation with that, two bands at 1060 and 1080 cm–1 attributed to spheroidal precipitates and another band at 1099 cm–1 related to the dissolution of platelet precipitates and the formation of microprecipitates make appearance in the spectra of carbon-rich Si at slightly lower temperatures and display higher intensities. This indicates that the enhancement of oxygen precipitation process is due to the effective formation of spheroidal precipitates having the lowest interfacial energy. The role of carbon in the enhanced precipitation process is discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Schottky barriers formed by depositing Au on n-type Ge have been used to study the antimony-vacancy complex (E center). Both hole and electron transitions have been observed because the formation of an inversion layer at the semiconductor surface enables minority carriers to be injected when the Schottky barrier is forward biased. It is argued that the E center in Ge has three charge states: double negative, single negative, and neutral. The free energy of electron ionization for the double acceptor level of the complex has been found to be ΔG(=/−)=0.294−4.2 kT (eV), where k is Boltzmann’s constant. Consequently, the position of the double acceptor level of the E center {E(=/−)=Ec−ΔG(=/−)} is temperature dependent. In moderately Sb-doped (NSb=1013–1015 cm−3) Ge crystals at equilibrium conditions half-occupancy of the double acceptor state of the Sb-V complex occurs when the Fermi level is at about Ec−0.20 eV. The single acceptor level of the E center is in the lower part of the band gap. The activation en...

We present results of a detailed study of X-ray, photoluminescence, and Raman measurements of hexagonal InN, In-rich In x Ga 1-x N (0.36 < x < 1) alloys, and InN samples annealed in oxygen.

The effect of enhanced hydrostatic pressure following heat treatment on the evolution of point defects in neutron-irradiated Czochralski-grown silicon is investigated using infrared spectroscopy. The behavior of oxygen-related defects, particularly of the VO and the VO2 centers, is mainly studied using samples subjected to heat treatment under hydrostatic pressure. It is observed that (1) pressure accelerates the annealing process of the VO defects and enhances the growth of the VO2 complexes and (2) the VO2 concentration is larger than expected from the corresponding decay of the VO defects. The faster decay of the VO defects is attributed to a pressure-induced decrease of their migration energy. The larger VO2 concentration is also discussed. One possible explanation is that pressure stimulates an additional mechanism for the formation of the VO2 defects, which involves the reaction of oxygen dimers with vacancies. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Czochralski-grown silicon samples subjected to high temperature–high pressure (HTHP) treatments in the range of 900 °C were irradiated with fast neutrons. Transmission electron microscopy measurements revealed the presence of oxygen precipitates (SiOx) and dislocation loops. The purpose of this work is to investigate the effect of these defects on the annealing behavior of neutron-irradiated induced oxygen-related defects, mainly the VO and the VO2 centers. To this end, infrared spectroscopy measurements were employed to monitor the conversion of the VO center (828 cm−1) to the VO2 center (890 cm−1 band) during isochronal anneals. In the untreated samples this conversion occurs around 300 °C. In our studies, we found that the annealing temperature (Tann) of the VO centers is lower than 300 °C. The value of Tann depends on the particular HTHP pretreatment. Actually, as a result of the precipitation process silicon self-interstitials (SiIs) are emitted and a number of them is bound at the Si/SiOx interface....

The infrared absorption technique was used for the studies of oxygen aggregates and related defects in 5 MeV neutron-irradiated Czochralski-grown silicon after heat treatment (HT) at 450 and 650 8C under hydrostatic pressures (HP) of 1 and 1.1 GPa, respectively. The results obtained showed that the formation processes of classical thermal double donors (TDDs) are reduced in neutron-irradiated Si subjected to HP/HT treatment. This result can be explained in terms of higher formation rates of V/O defects, the so-called A-centres. The enhanced oxygen precipitation and shallow thermal donor formation are observed after HP/ HT treatment at T/650 8C. # 2003 Elsevier B.V. All rights reserved.

The IR absorption and photoconductivity spectra of a double donor (TDD) family with ionization energies less than 70 meV in silicon were investigated using Fourier transform spectroscopy with a resolution down to 0.25 cm -1 . The values of line frequencies, widths, splitting and absorption cross sections for transitions from the ground to p-states (including high-excited states) were obtained. Determination of absorption cross sections was made using Hall data and concerted changes of boron and TDDi concentrations caused by neutralization of impurities under band gap illumination.

A survey of most recent studies of optical absorption, photoluminescence, photoluminescence excitation, and photomodulated reflectance spectra of single-crystalline hexagonal InN layers is presented. The samples studied were undoped n-type InN with electron concentrations between 6 × 10 18 and 4 × 10 19 cm -3 . It has been found that hexagonal InN is a narrow-gap semiconductor with a band gap of about 0.7 eV, which is much lower than the band gap cited in the literature. We also describe optical investigations of In-rich In x Ga 1-x N alloy layers (0.36 < x < 1) which have shown that the bowing parameter of b ∼ 2.5 eV allows one to reconcile our results and the literature data for the band gap of In x Ga 1-x N alloys over the entire composition region. Special attention is paid to the effects of post-growth treatment of InN crystals. It is shown that annealing in vacuum leads to a decrease in electron concentration and considerable homogenization of the optical characteristics of InN samples. At the same time, annealing in an oxygen atmosphere leads to formation of optically transparent alloys of InN-In 2 O 3 type, the band gap of which reaches approximately 2 eV at an oxygen concentration of about 20%. It is evident from photoluminescence spectra that the samples saturated partially by oxygen still contain fragments of InN of mesoscopic size.

The first data on surface gettering of background impurities and defects from the bulk of single-crystal undoped GaAs(111) wafers are reported. The wafers were 1.6 mm thick, with an initial electron density of (1–3)×1015 cm−3 and a mobility of 1500–2000 cm2/(V s) at room temperature. The wafers were cut from single crystals grown by the Czochralski method from a nonstoichiometric As-enriched Ga-As melt. Gettering was carried out during thermal treatment of the wafers in hydrogen at 400–850°C, with the preliminary deposited layer of Y or SiO2 1000 A thick. As a result of gettering, the charge carrier density decreased to 108–1010 cm−3, while the mobility increased to 7000 cm2/(V s).

The Hall effect measurements were conducted on Czochralski-grown silicon after implantation of erbium and two-step annealing at 700 °C and 900 °C. After the first step the formation of oxygen-related shallow donors was observed at E c in the range 20–40 meV and erbium-related donor centers at ≈E c -70 meV and ≈E c -120 meV. Along with the same oxygen-related shallow thermal donors and donor centers at ≈E c -70 meV, other donor centers at ≈E c -150 meV are formed following the 900°C anneal, instead of those at ≈E c -120 meV. The new donor states are of particular interest because of their possible involvement in the photoluminescence process. The obtained results for erbium-implanted silicon are compared with some fragmentary DLTS data found in the current literature on the donors with ionization energies less than 0.2 eV.

The effect of γ-ray radiation (60Co) on the photosensitivity of ZnO/CuIn3Se5 heterojunctions is studied. It is established that the spectral dependence of the photoconversion efficiency is retained if the heterojunctions are irradiated with γ-ray fluxes no higher than 2 × 1019 photon/cm2. Dependences of the open-circuit photovoltage and the short-circuit current on the γ-photon flux are studied. It is shown that the photoelectric parameters of heterojunctions remain unchanged under irradiation with the fluxes Φ 1017 photon/cm2, the photocurrent decreases monotonically, while the photovoltage exhibits a maximum, after which the photovoltage returns to the initial value. The potential for using the ZnO/CuIn3Se5 heterojunctions under the conditions of a high background radiation is established.

A gauge invariant approach to the Raman scattering from L––LO–L+ modes in heavily doped n-type semiconductors is developed. Sum rules expressing the charge conservation of electrons and ions are established for the allowed scattering mechanism (deformation potential and interband Frohlich interactions), forbidden mechanism (intraband Frohlich + Coulomb interactions), and the mechanism of charge density fluctuations. Impurity induced Raman processes for all three mechanisms are considered. Our predictions agree well with new experimental data on GaAs, GaN, and InN crystals. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Photoluminescence (PL) of n-InN grown by molecular beam epitaxy with Hall concentrations from 3.6 to 7.3 × 1017 cm–3 demonstrates dependences on carrier concentration, temperature, and excitation density which give evidences of a fast energy relaxation rate of photoholes and their equilibrium distribution over localized states. The structure of the PL spectra observed at 4.2 and 77 K in the energy interval from 0.50 to 0.67 eV indicates that a considerable part of holes is trapped by deep and shallow acceptors before the interband recombi- nation with degenerate electrons occurs. At room temperature, the band-to-band recombination of free holes and electrons dominates in PL. Experimental results on PL and absorption are described by model calculations under the assumptions of a band gap equal to 0.665–0.670 eV at zero temperature and zero carrier concentration and a non-parabolic conduction band with the effective mass at the G-point equal to 0.07 of the free electron mass. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Thermally induced defects in oxygen-rich silicon are the thermal donors (TDDS) and the so-called NL10 defects. These defects are formed by annealing at temperatures around 450 degrees C. Whereas the TDDS have a unique nature, some NL10 defects probably have different structures in differently doped silicon samples. NL10 defects were studied in P-doped silicon with electron paramagnetic resonance (EPR) and Hall effect measurements yielding the result that NL10 is a donor in this n-type silicon with a level deeper than 65 meV below the conduction band minimum. P is, however, not part of the defect. Electron nuclear double resonance (ENDOR) experiments have been performed on NL10 defects in B- and C-doped Si, while they were not possible in P-doped Si because of a short electron spin-lattice relaxation time. No ENDOR lines, except the 'distant' ENDOR lines of 11B,13C and 29Si respectively, were detected. This is in contrast to what was found previously in Al-doped Si. To explain this it is proposed that neither B nor C may be part of the NL10 defect in B- and C-doped Si respectively. In 17O-diffused B-doped Si a weak and rather broad ENDOR line was found which is not found in 16O-containing Si and which is attributed to 17O. In this case oxygen has much smaller quadrupole interactions than those found previously for NL10 centres in Al-doped Si and for TDDS. The identical EPR spectra of NL10 centres do not reveal structural differences in differently doped Si, for which our investigations have given some evidence.

The effect of γ irradiation on the photoluminescence decay dynamics in porous silicon is investigated. Growth of the photoluminescence intensity and decrease of the decay time in irradiated porous silicon are explained by a lowering of the barriers to recombination of spatially separated electrons and holes via tunneling. The γ irradiation of porous silicon leads to a greater dispersion of the decay time.

The results of an investigation of the donor centers in Czochralski-grown silicon ion-implanted with rare-earth impurities of Dy, Ho, Er, and Yb are presented. The formation of three groups of dominant donors with ionization energies less than 0.2 eV in silicon after annealing at 700 and 900 °C is discussed. The shallow donors at ≈Ec−40 meV are interpreted as thermal donors containing oxygen and intrinsic defects. The two other groups of donor states are identified as centers containing rare-earth ions.

Formation of new donors in Czochralski silicon (Cz‐Si) at temperatures T≥600 °C was studied. The contribution of deep donors was separated from those of other donor families with shallower states and in this way the formation kinetics of deep thermal donors was established. The results obtained make it possible to attribute these donor states at ≊EC−0.1 eV to ≊EC−0.25 eV to ribbonlike defects. Variations in the cross section of A‐center formation under gamma irradiation of heat‐treated Cz‐Si were found to correlate with formation of deep thermal donors.

Isovalent doping is an important process for the control of point defects in Si. Here, by means of infrared spectroscopy, we investigated the properties of the two main radiation-induced defects in Czochralski-Si (Cz-Si) the oxygen-vacancy (VO) and the carbon-oxygen (CiOi) centres. In particular, we investigated the effect of isovalent doping on the production, the thermal evolution, and the thermal stability of the VO and the CiOi defects. Additionally, we studied the reactions that participate upon annealing and the defects formed as a result of these reactions. Upon annealing VO is converted to VO2 defect although part of the CiOi is converted to CsO2i complexes. Thus, we studied the conversion ratios [VO2]/[VO] and [CsO2i]/[CiOi] with respect to the isovalent dopant. Additionally, the role of carbon in the above processes was discussed. A delay between the temperature characterizing the onset of the VO decay and the temperature characterizing the VO2 growth as well the further growth of VO2 after the complete disappearance of VO indicate that the VO to VO2 conversion is a complex phenomenon with many reaction processes involved. Differences exhibited between the effects of the various dopants on the properties of the two defects were highlighted. The results are discussed in view of density functional theory calculations involving the interaction of isovalent dopants with intrinsic defects, the oxygen and carbon impurities in Si.

It is demonstrated that the method of microwave photoconductivity developed previously for the study of ultrapure Si can be successfully employed in the qualitative diagnostics of pure high-resistivity GaAs. Data on the microwave photoconductivity of GaAs are in good agreement with the results of measurements of the Hall effect, C-V characteristics, and low-temperature photoluminescence.

This paper is devoted to the annealing studies of defects produced in carbon-rich Ge-doped Czochralski-grown Si (Cz-Si) by 2 MeV electron irradiation. The annealing temperature of vacancy-oxygen (VO) complexes, carbon interstitial-oxygen interstitial (CiOi), and carbon interstitial-carbon substitutional (CiCs) pairs as well as the formation temperature of vacancy-two oxygen (VO2) complexes are monitored as a function of Ge concentration. It has been established that the annealing of CiOi and CiCs defects remains practically unaffected by the Ge presence, whereas the annealing temperature of VO defects and the formation temperature of VO2 complexes are substantially lowered at Ge concentrations larger than 1×1019 cm−3. The hydrostatic component of elastic strains introduced by Ge atoms in the Si crystal lattice was calculated. It appears to be very small, at least insufficient to exert a pronounced effect upon the annealing behavior of radiation-produced defects. This conclusion is in line with what is obs...

The annealing behavior of the oxygen and carbon impurities in Czochralski grown silicon (Cz-Si) was investigated in electron- and neutron-irradiated materials. The irradiated samples were subjected to isochronal anneals of up to ∼1000 °C, and the evolution of oxygen and carbon concentrations was monitored by means of infrared spectroscopy from the amplitudes of the 1106 and 605 cm−1 bands of the two impurities correspondingly. It was found that the electron irradiation does not affect the temperature of annealing of oxygen, although in the neutron-irradiated samples the oxygen band begins to decay in the spectra at a lower temperature than that in the nonirradiated samples. This behavior could be determined by supersaturation of vacancies mainly liberated from disordered regions in the latter material. This assists the oxygen aggregation process. Regarding carbon evolution, it was found that in the irradiated samples the annealing out of the 605 cm−1 band occurs at a lower temperature than that of the non...

Formation processes of vacancy-oxygen (VO) and carbon interstitial-oxygen interstitial (CiOi) complexes in electron-irradiated Czochralski-grown Si crystals (Cz–Si), also doped with Ge, are investigated. IR spectroscopy measurements are employed to monitor the production of these defects. In Cz–Si with carbon concentrations [Cs] up to 1 × 1017 cm−3 and Ge concentrations [Ge] up to 1 × 1020 cm−3 the production rate of VO defects as well as the rate of oxygen loss show a slight growth of about 10% with the increasing Ge concentration. At high concentrations of carbon [Cs] around 2 × 1017 cm−3 the production rate of VO defects is getting larger by ~40% in Cz–Si:Ge at Ge concentrations around 1 × 1019 cm−3 and then at [Ge] ≈ 2 × 1020 cm−3 this enlargement drops to ~13%, thus approaching the values characteristic of lesser concentrations of carbon. A similar behavior against Ge concentration displays the production rate of CiOi complexes. The same trend is also observed for the rate of carbon loss, whereas the trend for the rate of oxygen loss is opposite. The behavior of Ge atoms is different at low and high concentrations of this isoelectronic impurity in Cz–Si. At low concentrations most isolated Ge atoms serve as temporary traps for vacancies preventing them from indirect annihilation with self-interstitials. At high concentrations Ge atoms are prone to form clusters. The latter ones are traps for vacancies and self-interstitials due to the strain fields, increasing the importance of indirect annihilation of intrinsic point defects. Such a model allows one to give a plausible explanation for the obtained results. A new band at 994 cm−1 seen only in irradiated Ge-doped Cz–Si is also studied. Interestingly, its annealing behavior was found to be very similar to that of VO complexes.