A. M. Ivanov

ANALYSIS OF DIVACANCY RELATED TRAPS INDUCED BY PROTON, NEUTRON AND GAMMA RADIATION IN HIGH RESISTIVITY SILICON DETECTORS

Abstract Defects with deep levels induced in high-resistivity silicon detectors by low and high radiation fluence of protons and neutrons are studied using capacitance and current DLTS. Numerical simulation of I-DLTS and C-DLTS spectra based on the model of charge carrier emission and redistribution of electric field in the detector enabled one to perform the detailed investigation of DLTS spectra. It has been shown that the main DLTS peak in the range of 200 to 260 K may be considered as a result of the interference of deep levels near the midgap – negatively charged divacancy VV− and the Ci–Oi complex. The model describing the broadening of the VV− component of the spectrum, which arises from the divacancy localization inside a cluster, is discussed. The results are compared with those obtained for gamma irradiation, for which the dominant contribution in DLTS spectra arises just from the Ci–Oi complex.

Relaxation of radiation damage in silicon planar detectors

The behavior of radiation‐induced carbon‐related defects in high‐resistivity silicon detectors has been investigated. The defects were introduced by α‐particle irradiation and investigated by deep‐level transient spectroscopy. An unusual defect behavior consists in low‐temperature annealing, including self‐annealing at room temperature, of the interstitial carbon Ci with a simultaneous increase of the Ci‐Oi‐complex concentration. The kinetic parameters of the process have been determined from the increase of the Ci‐center concentration versus time. Two annealing velocities have been observed, which arise from different heat treatments during the detector fabrication process.

Radiation hardness of wide-gap semiconductors (using the example of silicon carbide)

Results obtained in studying the effect of ionizing radiation on epitaxial layers and devices based on silicon carbide (SiC) are considered. It is shown that, in investigations of wide-gap semiconductors (WGS), account should be taken of how the rate of removal of mobile charge carriers—the standard parameter in determining the radiation hardness of a material—depends on temperature. The use of data obtained only at room temperature may lead to an incorrect assessment of the radiation hardness of WGS. A conclusion is made that the WGS properties combine, on the one hand, high radiation hardness of high-temperature devices based on these semiconductors and, on the other, the possibility of effective radiation-induced doping (e.g., for obtaining semi-insulating local regions in a material at room temperature).

Similarities and distinctions of defect production by fast electron and proton irradiation: moderately doped silicon and silicon carbide of n-type

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.

Elevated temperature annealing of the neutron induced reverse current and corresponding defect levels in low and high resistivity silicon detectors

A new aspect of degradation phenomena of neutron irradiated silicon detectors has been revealed which consists in the significant influence of carbon related defect transformation on the detector reverse current (I/sub rev/). The annealing of the reverse current at elevated temperatures and the corresponding changes of the deep level transient spectroscopy (DLTS) spectra of defects for fast neutron irradiated silicon detectors, fabricated on high (4-6) k/spl Omega/-cm, moderate (0.5-1.0 k/spl Omega/-cm) and low ( >

Diffusional creep as a stress relaxation mechanism in electromigration

The classical Blech description of the electromigration—stress interplay in interconnects treats the maximum electromigration compressive stress as a material constant (the yield stress). Systematic drift velocity and hillock topography observations in bare Al, anodized Al, and Cu conductors show this description to be valid only for relatively low current densities j. With increasing j, the actual stress surpasses this threshold stress and increases progressively, i.e., the stress is shown to adjust to j. The explanation of this adjustment evolves naturally from the attribution of the stress relief mechanism to creep (time-dependent plastic flow). A diffusional creep mode is the one most likely to explain the data. Coble creep is ruled out as the diffusional creep mechanism, while Nabarro-Herring creep may be a good candidate. The thresholds for electromigration and for the egress of excess atoms diffusing to the hillock surface are addressed in terms of linear tensions of dislocations and surface ledges.

Detection of strongly and weakly ionizing radiation by triode structure based on SiC films

Device structures based on thick and thin SiC epitaxialfilms have been studied as detectors of alpha particles and weak ionizationradiation (x ray and UV quanta), respectively. In the first case relatively no transistor effect is observed and the signal is formed similarly to that in a diode structure. The possibility of alpha particle spectrometry in spite of slow carrier transport via diffusion has been demonstrated. In the second case, the signal value of the transistor-like detector on applied voltage is investigated. Different modes are used: single alpha-particle detection and induced-current recording from fluxes of x ray and optical (UV) quanta. A superlinear rise in the resulting signal is observed with increasing voltage. The signal is amplified by a factor of several tens with respect to the value chosen for normalization. A description in terms of the phototriode model gives acceptable values for the main parameters: base width, diffusion length of electrons, and space charge of ionized impurities.

Effect of electron irradiation on carrier removal rate in silicon and silicon carbide with 4H modification

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 Energy Resolution Detectors Based on 4H-SiC

The spectrometric characteristics of the detectors based on 4H-SiC using 4.8-7.7 MeV a-particles were determined. The Cr Schottky barriers with areas of 1×10-2 cm2 were performed^by vacuum thermal evaporation on 4H-SiC epitaxial layers grown by chemical vapor deposition (CVD) with thickness 26 and 50 µm. The concentrations of the uncompensated donors into CVD epitaxial layers were (6-10) ×1014 cm-3, that allowed to develop a detector depletion region up to 30 µm using reverse bias of 400 V. The energy resolution less than 20 keV (0.34%) for lines of 5.0- 5.5 MeV was achieved that is twice as large of the resolution of high-precision Si-based detectors prepared on specialized technology. The maximum signal amplitude of 4H-SiC - detectors corresponding to the average electron-hole pair generation energy was found to be 7.70 eV.

Performance of p-n 4H-SiC film nuclear radiation detectors for operation at elevated temperatures (375 °C)

The spectrometric characteristics of nuclear radiation detectors based on 4H-SiC films with iondoped p+-n junctions have been studied for the first time in a temperature range from 25 to 375°C. The experiments with 5.8-MeV α particles were performed in a high-temperature chamber of special design. Factors related to the structural characteristics of both the initial silicon carbide and the ion-doped p+-n junctions are established, which limit from above the temperature interval of detector operation in a spectrometric regime. An increase in the efficiency of the diffusion-drift charge transport with increasing temperature has been observed, which is explained by an increase in the diffusion length of minority carriers.