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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.

Hall effect and conductivity measurements are taken on Si1 − x Ge x of n- and p-type at x ≤ 0.05. Much attention is given to electrical measurements over a temperature interval of 25 to 40 K where the mobility of charged carriers is strongly affected by alloy scattering. The partial mobility of electrons and holes due to this scattering mechanism is estimated for n-Si1 − x Ge x and p-Si1 − x Ge x at small x. Together with this, an effect of the presence of Ge atoms upon the ionization energy of phosphorus and boron impurities is investigated. Some points related to an inhomogeneous distribution of Ge atoms in Si1 − x Ge x are discussed.

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.

The free volume of the thermally stable vacancy center in n-FZ-Si:P has been probed by positrons. The defects were produced with 15 MeV protons, and then the irradiated material was subjected to the isochronal annealing. The positron lifetime has been determined over the temperature range ~ 30 K – 300 K; the samples-satellites have been characterized by Hall effect measurements. The microstructure of the center involves, at least, one atom of phosphorus and it manifests itself as a deep donor. The center is singly negatively charged and the cascade phonon-assisted trapping of positron proceeds over the length characteristic of the point defect, l0~3.62 a. u. Obeying ~ T–3law, the positron trapping cross section ranges 3∙10–12cm2(66K) to 2.5∙10–14cm2(266 K). The positron lifetimes ranging from ~240 ps to ~280 ps suggest that the atomic relaxation is directed inward towards the free volume of the deep donor involving, at least, two vacancies.

The recovery of shallow donor states of the atoms of phosphorus in n-FZ-Si:P material irradiated at the room temperature with 15 MeV protons was studied in the course of isochronal annealing. This process was investigated by the positron annihilation lifetime (PAL) spectroscopy and by low-temperature electrical measurements. The positron traps of a vacancy type manifesting themselves as deep donors have been revealed. These defects begin to anneal at ~ 593 K– 613 K; roughly estimated activation energy of the process is Ea ≈ 0.59 eV under the first order of reaction. The results suggest the involvement, at least, of one vacancy and the impurity atom of phosphorus in the microstructure of the deep donor.

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.

This paper reports experimental results on the production and annealing of oxygen-vacancy related (VOn, 1iOi, CiOiI, and CiCs) defects in Ge-doped Czochralski-grown silicon (Cz-Si) materials containing carbon. The samples were irradiated by 2 MeV fast electrons and the behavior of radiation-produced defects is studied by means of infrared (IR) spectroscopy, monitoring the relevant bands in spectra. Regarding the VOnfamily, it was found that the presence of Ge affects the annealing temperature of VO defects as well as their fraction that is converted to VO2defects. Both effects are discussed in relation with an impact of Ge on the concentration of self-interstitials that take part in the annealing of VO defects via two reaction paths VO + I → Oiand VO + Oi→ VO2. Furthermore, two bands at 1037 and 1051 cm-1are attributed to the VO5defect, although three other bands at 762, 967 and 1005 cm-1are believed to be associated with VnOmclusters containing carbon, most likely having a VOnCsstructure. Regarding carbon-related complexes, it has been established that the annealing of the 862 cm-1band belonging to the CiOidefect is accompanied by the emergence of the 1048 cm-1band previously assigned to the CsO2icenter. The evolution of the CiCsand the CiOiI bands is monitored and the identification of bands at 947, 967 and 1020 cm-1making their appearance in IR spectra over the temperature range where CiCsand CiOiI defects are annealed out is discussed.

Si1-xGex alloys with small atomic fraction of Ge, x≤ 0.05 are investigated. The Hall mobility of electrons in n-type materials was measured at cryogenic temperatures, T≤ 100 K. Taking into account the partial mobility due to charge carrier scattering by ionized centers and phonons it is possible to estimate the partial mobility associated with alloy scattering. It appears that this contribution to the electron mobility in n-Si1-xGex at low temperatures is important even at x≈0.01. The obtained results can be useful for understanding the nature of SiGe alloys and their transport properties.

The changes of the positron lifetime and loss/recovery of shallow donor states in n-FZ-Si:P material irradiated at the room temperature with 15 MeV protons have been investigated in the course of isochronal annealing. Thermally stable point radiation defects which begin to anneal at ~ 300 C° – 340 C° have been revealed; they manifest themselves as deep donors. It is argued that these defects involve, at least, more than one vacancy and the impurity atom (s) of phosphorus.

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.

We report studies of defects in electron-irradiated Czochralski-grown silicon (Cz-Si) subjected to thermal treatments at 1000oC and 1130oC with or without the application of high hydrostatic pressure of ~ 11 Kbars, prior to irradiation. The work is primarily focused on the impact of the pre-treatments on the production rate of the VO defect and its conversion to the VO2 defect. To this end, IR spectroscopy measurements were carried out and the amplitudes of the VO band (830 cm-1) and the VO2 band (888 cm-1) were monitored in the course of an isochronal anneal sequence up to ~ 550oC. Thermal treatments at 1000oC result in a reduction of the production rate of the VO defect. This rate however increases when pressure is applied during the treatment. The opposite behavior is observed for thermal treatments at 1130oC. The production rate of the VO increases slightly in heat treated samples but decreases substantially when high pressure is applied. Similar trends show the conversion of the VO to the VO2 defect for the corresponding treatments. The results are discussed taking into account the oxygen precipitates formed at the various treatments and their impact on the amount of primary defects available during irradiation which affects the production of the vacancy-oxygen defects.

We present infrared (IR) spectroscopy measurements on carbon-rich, germanium-doped Czochralski-grown (Cz-Si) subjected to irradiation with 2 MeV electrons. The study is focused on the effect of germanium doping on the production of carbon-related defects CiCs, CiOi and CiOi(SiI). For carbon concentrations [Cs] up to 11017 cm-3 the production of the defects increases with the increase of Ge content, for [Ge] up to 11020 cm-3. However, for carbon concentrations around 21017 cm-3 the production of these defects shows a decrease for samples with [Ge]=21020 cm-3 in comparison with those of [Ge]=21019 cm-3. The results are discussed taking into account the effect of germanium on the annihilation of vacancies and self-interstitials in the course of irradiations. In the first case, due to the temporary trapping of vacancies by Ge atoms in the course of irradiation, more self-interstitials are available for the production of carbon interstitials (Cs+ SiI Ci), leading finally to an increase of the carbon-related defects. In the second case, and for [Ge] of the order of ~1020 cm-3 or higher, Ge atoms tend to form large clusters. These clusters attract primary defects facilitating their annihilation on them. As a result, the availability of self-interstitials decreases, which finally leads to a decrease of the carbon-related defects.

The electron momentum distribution and microstructure of centers incorporating a vacancy (vacancies) and a group-V-impurity atom (P, As, Sb, or Bi) in oxygen-lean n-Ge crystals have been investigated by means of the angular correlation of the annihilation radiation (ACAR). The vacancy-group-V-impurity atom complexes have been induced by irradiation with 60Co γ – rays at Tirr. ≈ 280K. A split between the intensities of the high-momentum emission of the annihilation radiation measured before and after n-p-conversion has been revealed for the complexes containing smaller ion cores (P, As) and the larger ones (Sb, Bi), respectively. After n-p-conversion the electron density decreases slightly (but markedly) around the positron localized at the vacancy complexes incorporating P, Sb, and Bi impurity atom. This decrease is accompanied by a lessening of intensity of the high-momentum emission of the annihilation radiation thus bringing in a direct evidence of a multi-vacancy structure of the vacancy-group-V-impurity atom complexes after n-p-conversion; the electron density was found to be affected by the localized deep acceptor states related to these centers. The relaxation inward open volume is a common feature which is pronounced for As-containing complexes. Subvalent band states are suggested to contribute the high-momentum annihilation most markedly. The electron momentum density around the positron is due to rather by the elemental specificity of the surrounding atoms than by changes of the electron-positron many-body interaction in the vacancy-group-V-impurity atom complexes.

In the present work infrared (IR) spectroscopy measurements are taken on Ge-doped silicon samples irradiated by 2 MeV electrons to study the thermal evolution of VO defects and VO2 complexes upon annealing. The annealing behavior of these radiation defects was found to be complicated in the presence of Ge. The main reaction VO + Oi → VO2 leading to annealing of VO defects and formation of VO2 complexes turned out to be sensitive to concentrations of Ge impurity atoms in Czochralski grown silicon. These processes are discussed in some detail. Moreover, the rates of annealing reactions associated with self-interstitials can also be enhanced in silicon materials doped with Ge. The effects observed are most likely related to elastic strains due to Ge impurity atoms in the silicon lattice.

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.

Comparative study of the effect of successive (up to fluences of 3 × 1016 cm−2) irradiation with 900 keV electrons of samples made of FZ-Si and 4H-SiC (CVD) has been performed for the first time. Measurements on initial and irradiated samples were made using the van der Pauw method for silicon and the capacitance-voltage technique at a frequency of 1 kHz for silicon carbide. In addition, the spectrum of the defect levels introduced was monitored by the DLTS method for SiC. The carrier removal and defect introduction rates were determined for the two materials. It was found that the rates of defect introduction into FZ-Si and 4 H-SiC (CVD) are close to eachy other (∼0.1 cm−1), which is largely due to the almost identical threshold energies of defect generation.

High-momentum component (HMC) of the electron–positron annihilation has been detected by the angular correlation of annihilation radiation (ACAR) technique in order to obtain elementally specific information about the ion cores of the donor–vacancy complexes (DV) formed by irradiation with 60Co γ-rays at Tirr.≈280 K in oxygen-lean n-Ge doped with group-V donors (D=As, Sb, and Bi). The probability of annihilation of positrons with the core electrons of DV complexes reconstructed from ACAR spectra increases in passing from AsV to SbV and BiV complexes. This increase correlates with the shift of the D atom from its regular position towards the vacancy site predicted by the results of spin-density functional modeling study. The data obtained suggest inward relaxation of the ion cores of DV complexes (including the one directed inward towards the vacancy).

Radiation-produced defects in doped and nominally undoped n-GaN with charge carrier concentrations in a range of 4 × 10 16 cm -3 to about 2 × 10 18 cm -3 are investigated. Layers of n-GaN are irradiated with fast electrons at 0.9 MeV, 60 Co gamma rays and protons at 150 keV. The production rates of radiation defects in n-GaN are estimated and compared with literature data. Annealing processes of radiation defects in n-GaN in the temperature range 100-700 °C are also discussed. The annealing behavior appears to be complicated. Two temperature intervals, from T= 100 to 400°C and from T = 500 to 700°C, are characteristic for modification and annealing processes of radiation-produced defects in n-GaN.

Results of DLTS and high-resolution Laplace DLTS measurements of electrically active defects induced in phosphorus-doped dilute Ge-rich SiGe (0⩽[Si]⩽6 at%) samples by irradiations with 60 Co gamma-rays, fast neutrons and 1–3 MeV Si ions and by ensuing annealing are presented in the work. It has been found that the DLTS spectra of these germanium rich SiGe samples irradiated with gamma-rays are qualitatively similar to the spectra of similarly irradiated Ge samples, which do not contain Si. The DLTS spectra of the gamma-irradiated samples are dominated by the E-center (vacancy–phosphorus pair). This indicates that silicon impurity atoms are not effective traps for vacancies in Ge at room temperature. Further, we have found no evidence for possible interactions of Ge self-interstitial atoms with Si atoms upon room temperature electron irradiation of SiGe samples. The presence of Si impurity atoms does not influence significantly the annealing behavior of the E center in Ge-rich SiGe. Thirty-minute heat treatments of the gamma-irradiated samples at 300 °C have resulted in complete removal of radiation-induced damage. DLTS spectra of the SiGe samples after low dose neutron irradiation resemble those observed after gamma irradiations, however, in the neutron-irradiated samples a few more minor DLTS peaks have been observed. The neutron-radiation-induced defects can be removed by anneals at 300 °C. The situation in ion-implanted material is more complex. Point defects, which dominate the DLTS spectra of electron-irradiated SiGe samples, are not the main electrically active traps in the ion-implanted samples. The Laplace DLTS spectra of the implanted samples show evidence of broader features characteristic of defect clusters. The implantation-induced damage is much harder to remove by heat treatments compared to the radiation-induced one. Significant concentration of electrically active traps remain in SiGe samples implanted with high doses of ions even after anneals at 500 °C.

The thermal evolution of multioxygen-vacancy (VO n ) centers produced in electron-irradiated Czochralski-grown Ge-doped Si was studied by means of IR spectroscopy. Two groups of samples with low [Ge] ≤ × 10 17 cm -3 and high [Ge] = 2 × 10 20 cm -3 were used. We found that the annealing temperature of vacancy-oxygen complexes (A-centers) produced in the course of irradiation at room temperature is substantially decreased in the samples with high [Ge]. This effect is explained taking into account an influence of the elastic stresses due to Ge atoms in the Si lattice on the migration barrier of A-centers as well as the rate of oxygen-related reactions, i.e. VO + O i → VO 2 , VO + Si I → O i , etc. We also found that the ratio of A-centers converted to VO 2 defects is smaller in the material with high [Ge]. The same is also true for the conversion reaction VO 2 + O i → VO 3 . Contrary, the next reaction VO 3 +O i →VO 4 shows a markedly enhanced rate if the Ge content is high. This observation can be explained considering the effects of Ge-induced stresses in the Si lattice on the successive trapping of oxygen atoms by A-centers and other VO n complexes as well as on the enhanced diffusivity of oxygen.

Angular correlation of annihilation radiation technique (ACAR) has been used for studying a microstructure of the vacancy-group-V-impurity complexes (DV) formed by irradiation with 60Co γ – rays at Tirr. ≈ 280K in oxygen-lean n-Ge doped with group-V-impurity atoms As, Sb, and Bi. The probability of annihilation of positrons with the core electrons of DV complexes to be reconstructed from ACAR spectra has been analyzed on the basis of Chapman-Kolmogorov formalism; the Coulomb repulsion is proved to regulate the penetration of a positron into Ge4+ and D5+ ion cores. In passing from AsV to SbV and BiV complexes the ion cores D5+ are found to contribute more effectively to the probability of the positron annihilation in the core region. These data correlate well with the augmentation of the entropy of ionization (4S ~ 2,9 ÷ 4,2K) observed by means of capacitance transient techniques with the use of Au-Ge Schottky barriers in the same row of a similar vacancy-impurity complexes. The results obtained by ACAR spectroscopy suggest the full-vacancy configuration of DV pair with relaxation of atoms inward towards the vacancy.

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.

Defect reactions occurring in Ge:Bi, O crystals upon electron and gamma irradiations at room temperature and the following isochronal annealing in the temperature range 80–350 °C have been studied by means of deep level spectroscopy (DLTS) and high-resolution Laplace DLTS. It is shown that bismuth and oxygen impurity atoms are the most effective traps for mobile vacancies created by irradiation in the crystals. Both the vacancy–oxygen (VO or A center) and vacancy–bismuth (Bi–V or E center) defects in Ge have three charge states and introduce two energy levels into the gap. The ratio of concentrations of the VO and Bi–V centers in as-irradiated samples depends on the relative concentrations of interstitial oxygen (Oi) and substitutional bismuth (Bis) atoms. Annealing studies demonstrate that in the temperature range 120–150 °C the concentration of the Bi–V center increases. This has been associated with the dissociation of VO that occurs in the range 100–150 °C. In consequence the proposed mechanism is the release of vacancies from the A center which are subsequently trapped by the Bi impurity atoms to form the Bi–V E center. It is suggested that the enhanced disappearance of the Bi–V centers in electron-irradiated oxygen-rich Ge samples is associated with the interaction of the E centers with mobile Ge self-interstitials released from oxygen-related traps at T ⩾ 1 4 0 ° C .

Electronic processes associated with changes in the charge states of the vacancy–oxygen center (VO or A center) and vacancy–group-V-impurity atom (P, As, Sb or Bi) pairs (E centers) in irradiated germanium crystals have been studied using deep level transient spectroscopy (DLTS), high-resolution Laplace DLTS and Hall effect measurements. It is found that the electron emission and capture processes related to transitions between the doubly and the singly negatively charged states of the A center and the E centers in Ge are phonon-assisted, i.e., they are accompanied by significant vibrations and re-arrangements of atoms in the vicinity of the defects. Manifestations of the phonon involvements are: (i) temperature-dependent electron capture cross-sections which are well described in the frame of the multi-phonon-assisted capture model; (ii) large changes in entropy related to the ionization of the defects and, associated with these, temperature-dependent positions of energy levels; and (iii) electron emission via phonon-assisted tunneling upon the application of electric field. These effects have been considered in detail for the vacancy–oxygen and the vacancy–donor complexes. On the basis of a combined analysis of the electronic processes a configuration-coordinate diagram of the acceptor states of the A and E centers is plotted. It is found that changes in the entropy of ionization and the energy for electron emission for these traps follow the empirical Meyer–Neldel rule. A model based on multi-phonon-assisted carrier emission from defects is adapted for the explanation of the origin of this rule for the case of electronic processes in Ge.

Radiation-produced defects in heavily doped n-Si with charge carriers concentrations n ⩾ 3 × 10 18 cm - 3 are investigated. The results obtained in these radiation experiments provided evidence that most Frenkel pairs produced after 2.5 MeV electron irradiation at T = 4.2 K are present in irradiated materials but they are not seen in electrical measurements. At room temperature a majority of Frenkel pairs produced are separated into the constituent defects forming impurity-related complexes. Two prominent stages of defect annealing are observed at temperatures above T = 300 K . Complete recovery of the concentration and mobility of charge carriers in irradiated materials takes place around T = 800 K .

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.

Effects of compressive stress on oxygen agglomeration processes in Czochralski grown silicon heat treated at T= 450OC, used as a reference temperature, and T= 600OC to 800OC are investigated in some detail. Compressive stresses of about P= 1 GPa lead to enhanced formation of Thermal Double Donors in materials annealed over a temperature range of T= 450OC – 600OC. It has been shown that the formation of thermal donors at T= 450OC under normal conditions and compressive stress is accompanied with loss of substitutional boron. In contrast, the concentration of the shallow acceptor states of substitutional boron in silicon annealed under stress at T≥ 600OC remains constant. An enhancement effect of thermal donor formation is gradually weakened at T≥ 700OC. The oxygen diffusivity sensitive to mechanical stress is believed to be responsible for the observed effects in heat-treated silicon.

A probing of the atomic environment of positron in Cz-Si single crystal heat-treated at T=600C and T=450C has been performed by one-dimensional angular correlation of annihilation radiation (ACAR). It has been established that positrons get trapped by the oxygen-related complexes. The penetration of positrons into the core region of surrounding atoms results in emission of the elementally specific high-momentum annihilation radiation. The processes of expelling of positron from ion cores and its penetration into the core region are regulated by the potential barrier (to be considered as the Coulomb’s one as a first approximation). The characteristic electron-positron ion radius and the probabilities of correlated events of the highmomentum annihilation are due to the chemical nature of the ion cores of atoms involved in the composition of the oxygen-related complexes. The interpretation of the results is based on the notion of the positron localization in the field of negative effective charge resulted from comparatively high electron affinity of the oxygen impurity atom. The presence of a free volume (perhaps, a vacancy) as well as the carbon atom in the microstructure of the oxygen-related positron-sensitive thermal defects is briefly discussed.

Deep states produced during γ irradiation of germanium have been compared with the defects produced by 1 and 3MeV silicon ion implantation. The deep states have been studied using DLTS and Laplace DLTS techniques. Isochronal annealing has been used to investigate the defect evolution and stability over the range 100 to 500°C. It is found that while irradiation damage can be removed with a very low thermal budget, the implantation damage is more complex and much more difficult to remove. By comparing low (1010cm-2) and high (1012cm-2) implantation doses it appears that both the complexity and stability of defects increases with increasing dose. Similar experiments have been performed on Ge rich Si1-xGex (x=0.992). The focus of this work has been on vacancy related defects. It is believed that the diffusion of both acceptors and donors is vacancy mediated in Ge and so vacancy clusters rather than interstitial clusters are expected to be the technologically significant defect in enhanced diffusion. The significance in terms of junction leakage and generation currents are discussed in the paper in the context of the observed defect reactions.

Cz-grown, carbon-doped silicon samples were irradiated by fast neutrons. We investigated the annealing behaviour of oxygen-related defects, by infrared spectroscopy. We studied the reaction channels leading to the formation of various VmOn defects and in particular the VOn defects formed by the accumulation of oxygen atoms and vacancies in the initially produced by the irradiation VO defects, as the annealing temperature ramps upwards. We mainly focused on bands appearing in the spectra above 450 oC. A band at 1005 cm-1 is found to be the convolution of two bands at 1004 and 1009 cm-1. The latter band has the same thermal stability with the 983 cm-1 of the VO4 defect and therefore is also attributed to this defect. The former band has the same thermal stability with three other bands at 965, 1034 and 1048 cm-1. These four bands may be attributed to VOn (n=5,6) defects, although other VmOn complexes are also potential candidates. Furthermore, we found that pre-treatments of the samples at 1000 oC, with or without the application of high hydrostatic pressure lead to an increase in the concentration of the VO2, VO3 and generally VOn defects in comparison with that of the untreated samples.

Thermal treatments of Czochralski-grown Si at T = 450, 600 and 650°C, under high hydrostatic pressure of P 11 kbar, introduce thermal donors and various structural defects, as for example oxygen precipitates. Neutron irradiation of such samples results first in the formation of oxygen-vacancy complexes, mostly VO defects. Upon annealing, the VO defects evolve in larger clusters via the accumulation of oxygen atoms and vacancies in the initial VO core, leading to the formation of V m O n defects. We focus on the study of the effect of pre-treatments on the production and evolution of the various V m O n defects upon isochronal annealing. The observed changes and variations in the IR spectra and the evolution curves in comparison with the corresponding ones of an initially untreated sample are discussed and some explanations are offered. The most important finding of this work is that the concentrations of the VO 2 and the VO 3 defects are reduced in the sample pre-treated at 450 °C, an indication of interaction between thermal donors and radiation-induced defects.

A comparison study of radiation damage in n-type silicon grown by the floating zone technique and n-type silicon carbide grown by the sublimation epitaxy technique was carried out for the first time under the same irradiation conditions. This comparison is drawn for an energy region of fast electrons at ≈ 1 MeV where Frenkel pairs as primary defects, i e the self-interstials bound to their parent vacant sites at a distance of a few lattice spacings, are produced most effectively. The removal rates of charge carriers in n-Si and n-SiC (4H and 6H) were found to be about 0.23 cm-1 and 0.015 cm-1, respectively. The possible reasons of the observed difference are briefly discussed.

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)

The IR spectra of all three Si isotopes in the form of bulk single crystals (28Si with an enrichment of more than 99.9%, and 29Si and 30Si with an enrichment of more than 90%) have been studied at T = 300, 17, and 5 K in the spectral range 550–1200 cm−1. The IR active local vibrational modes (LVM) of Si-12C centered at 605 cm−1 and Si-16O-Si quasi-molecules in the region of 1136 cm−1 for all the Si isotopes, in comparison with Si possessing a natural isotopic composition, as well as their isotopic shift at 300 and 17 K, have been determined. The dependence of the shape of the antisymmetric stretching vibration band for 28Si-16O-28Si in the spectrum of 28Si on spectral resolution has been studied. The possibility of generalizing the IR spectroscopy method for the determination of carbon and oxygen impurities in Si possessing a natural isotopic composition to monoisotopic Si have been discussed.

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...

The measurements of one-dimensional angular correlation of the annihilation radiation (1D-ACAR) have been carried out for BN, AlN, and GaN as well as for some related materials that have been used as the reference samples for the analysis of results. The electron–positron ion radii reconstructed by 1D-ACAR for the cation and anion sublattices of the nitrides as well as the estimated average electron density around the positron suggest that: (a) the positron annihilates in the vacancy complexes N Ga V N in GaN and N Al V N in AlN, and (b) the cation nearest neighbours are, probably, shifted inward to the V N vacancy where the electron density is sufficiently lower in comparison with that estimated for the bulk.

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.