Annealing of γ-ray irradiated lithium compensated p-type silicon

Abstract

Annealing behavior of electrical properties and photoluminescence spectra both at 77 °K in electron-irradiated melt-grown n-GaAs were investigated. Defects electrically active in the Hall mobility and carrier removal anneal through two stages centered at 250° and 460 °K. From the temperature dependence of carrier concentration the existence of a defect level located near 0.15 eV below the conduction band is supposed. Several emission bands are resolved at 1.51, 1.47, 1.415, 1.305 and ～1.2 eV in photoluminescence experiments. Electron irradiation (1.5–2.0 MeV) causes a remarkable decrease in emission intensity of 1.51 and ～1.2 eV bands. Recovery of emission intensity occurs remarkably when samples are annealed to 520 °K which would correspond to the 460 °K annealing stage for carrier concentration and Hall mobility. The 250 °K annealing stage is not observed in photoluminescence experiments. The 1.415 eV peak appears clearly after irradiation and grows remarkably with the 520 °K annealing, especially in Si-doped samples, resulting in large reverse annealing. This band is tentatively speculated to be a complex of Si on As site with As vacancy. Moreover, in samples doped with Te a new emission band at 1.305 eV (9500 Å) is observed after 470°–620 °K annealing.     

Measurement of stored energy of KCl after 4·6°K reactor irradiation

Five KCl single crystals were irradiated at 4·6°K in the core of the Munich Nuclear Reactor for periods of 100 sec, 10 min, 1 hr or 10 hr, respectively. After irradiation the stored energy of the samples was measured in a differential-heat-flow calorimeter at two different heating rates: 0·29 and 1·1°K/min. At 0·29°K/min peaks of stored energy release were resolved at 21°K, near 27·5°K, at 32·5°K, at 42·5°K and near 50°K. An attempt was made to evaluate the corresponding activation energies using two different methods (see Table 1 in the text). The annealing stages at 21 and 32·5°K correspond to first order kinetics. The annealing stages at 42·5 and near 50°K are not of first order. A similar experiment was performed on KBr single crystals and is reported in the preceding paper. The results are compared with annealing studies on low temperature X-irradiated KCl and KBr crystals. From both our experiments it follows that also during reactor irradiation at 4·6°K ionization mechanisms of defect production should be responsible for the four observed low temperature recovery peaks; only defect recovery at higher temperatures may be at least partially explained by recombination of collision produced defects, i.e. the typical neutron irradiation effect as it takes place in metals.     

High-dose reactor irradiation of iron at 4.6 K: Dose and recovery curves of electrical resistivity

The increase of residual resistivity ?_o of iron during reactor irradiation at 4.6 K has been studied up to a fast neutron dose as high as 1.07 × 10¹⁹ n/cm². The outstanding result is a negative curvature of the differentiated dose curve which probably has to do with the ferromagnetic nature of Fe. Isochronal annealing showed pronounced stages I and II but only little recovery between 300 and 400 K (formerly called stage III).     

Measurement of stored energy of KBr after 4·6°K reactor irradiation

Four KBr single crystals were irradiated at 4·6°K in the core of the Munich Nuclear Reactor for periods of 100 sec, 10 min or 1 hr, respectively. After irradiation the stored energy of the samples was measured in a differential-heat-flow calorimeter at heating rates of 0·29°K/min and 1·1°K/min. At 0·29°K/min peaks of stored energy release were resolved near 11 and 20°K and at 25, 38 and 45°K. An attempt was made to evaluate the corresponding activation energies using two different methods (see Table 1 in the text). The 25°K annealing stage is due to a first order recombination reaction. The anneling states near 20, at 38 and at 45°K do not correspond to first order reactions. Our results are compared with annealing studies on low temperature X-irradiated KBr crystals. A similar experiment was performed on KCl single crystals and is reported, together with a more detailed comparison and discussion of both experiments, in a later paper[14].     

The bulk effect of point defects on young's modulus in electron irradiated copper

Abstract

Pairs of copper samples—one for electrical resistivity, the other for Young's modulus measurements - were irradiated simultaneously at 120°K with 3 MeV electrons up to an integrated dose of 2 × 10²⁰ el/cm². The effect of dislocation pinning and the bulk effect of point defects on Young's modulus E could clearly be separated. The following relation between the bulk effect ΔE/E and the resistivity increase Δρ[Ωcm] was found: ΔE/E = ?25 × 10⁴ × Δρ. Besides strong annealing in stages II and III (180–300°K) and some annealing between 300–500°K, stage V annealing (500–600°K) also was found. In stage III the resistivity annealed more than Young's modulus. whereas the converse occurred in stage V. These measurements are discussed in connection with the electron microsopical observation of point defect clusters after electron irradiation at 120°K and heating to room temperature.

Probenpaare, bestehend aus einer Widerstandsprobe und einer Probe zur Messung des Elastizitätsmoduls, wurden gleichzeitig bei 120°K mit 3 MeV-Elektronen bis zu einer Dosis von 2 × 10²⁰ el/cm² bestrahlt. Die direkte Reein-flussung des E-Moduls durch die im Gitter verteilten Punktdefekte (Volumeneffekt) konnte getrennt von der Beeinflussung durch Versetzungsverankerung gemessen werden. Es ergab sich dabei folgende Beziehung zwischen relativer Modulanderung ΔE/E und strahlungsinduziertem Widerstand Δρ[Ωcm]: ΔE/E = ?25 × 10⁴ × Δρ. Neben starker Erholung in den Stufen II und III (180–300 °K) und schwacher Erholung zwischen 300–500°K wurde auβerdem Stufe V (500–600°K) beobachtet. In Stufe III erholte sich der Widerstand starker als der E-Modul, wahrend in Stufe V das umgekehrte der Fall war. Die Messungen werden diskutiert in Zusammenhang mit der elektronenmikroskopischen Beobachtung von Punktdefektclustern nach Elektronenbestrahlung bei 120°K und anschlieβender Erwärmung auf Raumtemperatur.     

Low temperature photoconductivity in electron - irradiated p-type Si

The photoconductivity spectra of p-type silicon irradiated at ～15 °K with 1.2 MeV electrons were studied in the wavelength range from 1.2 to 5.5 μ at temperatures from 23 to 80 °K. The 3.9 μ photoconductivity band appears immediately after irradiation in all crystals already at low temperatures, giving further evidence that it is due to the divacancy formed directly during irradiation by electrons. Three main annealing stages of the photoconductivity have been observed; (a) below 160 °K, (b) 160–250 °K, and (c) 280–360 °K. A radiation-induced deep level at E_v , +(0.12±0.02 eV disappears upon annealing at stage b. The annealing behavior of the spectra depends strongly on the measuring temperature. The dependence of the spectra on chopper speed was also investigated.     

Ultrasonic detection of the pinning of dislocations by point defects in lead-I determination of migration energies

The ultrasonic attenuation of a γ-irradiated, deformed, single-crystal of lead has been measured between 77 and 270 K. Constant heating rate and isothermal anneals after low temperature irradiation yielded two dislocation pinning stages centered at 140 and 200 K and two dislocation depinning stages centered about 170 and 250 K. For an unirradiated sample one pinning stage centered at 170 and one depinning stage centered at 250 K were observed. Activation energies were calculated from isothermal anneals using an eigenfunction expansion model to be 0·16±0·04 and 0·36±0·05 eV for the pinning stages in the irradiated crystal and 0·28±0·05 eV for the pinning stage in the unirradiated crystal. The activation energy calculated from the same isothermal anneals using a Cottrell-Bilby analysis was 0·23±0·03 eV for the low temperature pinning stage in the irradiated crystal. The other activation energies were not changed. The discrepancy is discussed in Part II.     

Phase diagram of Bi up to 140 kbars

The phase diagram of Bi has been studied by resistometric techniques in the temperature range of 30 to 300°K up to pressures of 140 kbars. Using the original Bridgman phase notation, the phase transitions I–II, II–III, I–III, III–IV and V–VI were observed. Two new phases, designated VIII and IX were observed in this region. The triple points occurring between I–II–III near 29.5 kbars and 160°K, between IV–V–VIII near 55 kbars and 240°K, between V–VI–VIII near 72 kbars and 255°K and between VI–VIII–IX near 135 kbars and 250°K. Earlier measurements were adjusted to the 1970 Drickamer pressure scale and compared to the present results. A phase diagram is proposed for pressures to 140 kbars. Calculations of the volume changes and latent heats of transformation are made near the triple points I–II–III, IV–V–VIII and V–VI–VIII using the measured volume changes of Bridgman for the I–II, IV–V and V–VI transitions. The latent heat associated with the III–IV transition was calculated using the volume data of Bridgman to be less than ? 2 cal/mol.     

Low energy boron and phosphorus implants in silicon (a) electrical sheet measurements

Silicon wafers were implanted in 〈111〉-direction with boron and phosphorus ions of 7 keV at room temperature. Doses between 10¹² and 10¹⁸ ions/cm² were applied. After successive annealing steps the electrical properties of the implanted layers have been determined by Hall effect and sheet resistivity measurements. The annealing characteristics of the implants depend on ion dose and species. Three annealing stages can be distinguished: (I) the temperature range below 500°C, (II) 500—700°C, (III) 700—900°C.

After annealing at 90°C the apparent electrical yield is proportional to dose for all implants and amounts to approx. 80 per cent for boron and 40 per cent for phosphorus.

Sheet resistivity vs. dose curves were derived for the annealing temperature of 400°C and used for the fabrication of position sensitive detectors. The position characteristics were found to be linear within ～1 per cent for resistive layers as long as 20 cm.     

The annealing of damage in ion implanted gallium arsenide

Photoluminescence measurements at 77°K and Rutherford scattering of 450 keV protons were used to study radiation damage and annealing in ion implanted GaAs. The characteristic band edge luminescence (8225 Å) in GaAs is completely quenched by ion implantation. Photoluminescence measurements on samples which were isochronally annealed show a single annealing stage at 600°C. A luminescence peak at 9140 Å is introduced into the spectra of all implanted and annealed samples. This peak is attributed to an acceptor level created by As vacancies. The intensity of the peak is greatly reduced by protecting the surface of implanted layers with SiO₂ during annealing. Rutherford scattering measurements on isochronally annealed samples reveal two annealing stages. A 300°C annealing stage is observed on samples which have an initial aligned yield less than random while a 650°C stage is observed on samples which have an initial aligned yield equal to random.     

Role of nickel and manganese in recovery of resistivity in iron-based alloys after low-temperature proton irradiation

This study investigates the recovery of electric resistivity in pure iron, Fe–0.6Ni and Fe–1.5Mn as related to isochronal annealing following 1 MeV proton irradiation at lower temperature than 70 K, focusing on the relationship between solute atoms and irradiation defects. Both nickel and manganese prevent stage I_D recovery, which corresponds to correlated recombination. Stage II recovery is also changed by the addition of a solute, which corresponds to the migration of small interstitial clusters. In both pure iron and Fe–0.6Ni, no evident difference was observed in the stage III region, which corresponds to the migration of vacancies. In contrast, two substages appeared in the Fe–1.5Mn at a higher temperature than stage III_B appeared in pure iron. These substages are considered to represent the release of irradiation-induced defects, which was trapped by manganese.     

Neutron irradiation-induced enhancement of electronic carrier transport in ZnO

Irradiation of ZnO single crystals by thermal neutrons with a dose up to 7×10¹⁷ cm^?2 and subsequent annealing at 400 °C for 1 h leads to a significant increase in majority carrier mobility and concentration in this material, with the corresponding decrease of its sheet resistance. Additionally, cathodoluminescence spectra taken before and after neutron irradiation are consistent with the growing carrier lifetime. The observed effects are attributed to irradiation-induced formation of electrically active species of interstitial Zn and improvement of lattice crystallinity due to annealing.     

Thermal Neutron damage in cadmium

The isochronal annealing of the damage produced by thermal neutron irradiation of cadmium at 3.6 °K has been studied for several initial doses which vary by a factor of 1000. The recovery results show a strong dependence upon initial dose. This effect, which is not seen to this extent in the fcc metals, cannot be accounted for by an irradiation annealing mechanism. In contrast to the observation of two processes involving long range defect migration for several fcc metals only one process, at high temperatures, is discernable from isochronal annealing of Cd. The presence of another process at low temperatures is clearly established by other means. Irradiation annealing effects observed during the production of damage at high defect concentrations indicate that the spontaneous annihilation volume between the defects of a new capture event and the defects from an earlier event is 80 atomic volumes. Other results suggest that damage production and recovery mechanisms may be associated with the anisotropic nature of the cadmium hexagonal lattice.     

Illumination induced annealing in electron-irradiated p-type silicon

Illumination with white light during isochronal annealing in p-type Si irradiated with 2 MeV electrons at 77 K introduces stages of recovery at around 85 and 140 K. These stages recover about 90% of carriers removed by the irradiation.     

Measurement of internal friction and shear modulus of aluminium-magnesium alloy after neutron irradiation at 78 K

The internal friction and shear modulus of polycrystalline Al + 3 at.% Mg was studied as a function of temperature after fast neutron irradiation, at liquid nitrogen temperature (78 K). The initial increase of shear modulus after irradiation is mainly due to the dislocation pinning of the irradiation induced defects. The further increase of shear modulus during annealing is caused by the bulk-effect. The recovery of shear modulus up to room temperature is similar to that of the residual electrical resistivity after a low temperature neutron irradiation. However, we may point out that in contrast to stage II, in stage III we observe a recovery of shear modulus that is distinctly more pronounced than that of electrical resistivity. The temperature dependence of internal friction, before irradiation, shows a peak at 230 K. After neutron irradiation we observe no peak in the temperature region, from 90 K to 300 K.     

Impurity dependence of the low temperature annealing in n-type germanium

Lightly doped n-type Ge, irradiated at liquid He temperatures with 1 MeV electrons, exhibits a large thermal recovery stage at 50–70°K. We have found that the rate at which this stage anneals depends on the type of group V impurity used to dope the sample. We Propose that impurity complexes are involved in this annealing stage. We have also observed the same impurity dependence when this annealing stage is destroyed by radiation annealing at liquid He temperatures. This suggests that one of the defects produced during irradiation is free to migrate at very low temperatures.     

Die Verfestigungserholung von plastisch verformten Steinsalzeinkristallen

Cylindrical rock salt single crystals have been plastically deformed by compression in the [001]-direction at room temperature to shear stresser τ _E of 200 N/cm² and 350 N/cm², respectively. Isochronal annealing experiments reveal, that workhardening recovers at >300° C. The characteristic annealing temperature was found between 400° C and 450° C. At 600° C the residual workhardening still amounts to 15–20%. The isochronal reduction of screw dislocation density between 400 and 600° C shows qualitatively the same behaviour as recovery of workhardening. From the isothermal annealing curves of the samples deformed to 200 N/cm² the activation energy for recovery of workhardening was found to be about 1 eV. Assuming that the kinetics of recovery can be explained by processes distributed in activation energy, an approximate spectrum of activation energies (with a maximum arising at ～1 eV) has been evaluated. The results show that recovery of workhardening after low deformation (stage I of the stress strain curve) is mainly due to the dislocations.     

Absorption measurements in neutron irradiated silicon

Silicon samples have been neutron irradiated at 76 °K with fluences sufficient to allow measurement of the 1.7 μ divacancy band at 76 °K. The growth of the divacancy concentration and the recovery of the edge absorption were studied as a function of annealing temperature between 76 °K and 550 °K. Immediately after irradiation the divacancy concentration is about 25 per cent of its maximum value which is attained at 330 °K, the temperature at which the divacancies begin to anneal out. Increases in the 1.7 μ band intensity and recovery of the edge absorption can also be achieved at 76 °K by illuminating the sample with intense sub-bandgap light or white light. The experimental results suggest a neutron-induced cluster model in which the cluster is a vacancy-rich region whose annealing characteristics are controlled by the liberation and motion of vacancies. The injection effects can be explained by analogy to the charge state dependent mobility of the Si vacancy.     

Defect study on electron irradiated GaAs by means of positron annihilation

Measurements of the positron lifetime and Doppler-broadened annihilation-radiation have been performed in electron-irradiated GaAs. The positron lifetime at the irradiation induced defects was 0.250 ns at 300 K. The defect clustering stage was found to occur at around 520–620 K, and the coarsening and annealing stage is believed to be above 620 K. Similar annealing stages were also observed in GaAs lightly doped with Si (0.2×10¹⁸ cm^–3). Both the lifetime and the S-parameter in the irradiated GaAs were found to decrease with temperature from 300 K to 100 K, suggesting the coexistence of shallow traps in electron irradiated GaAs.     

Effect of partial recovery of zinc surface at room temperature after basal plane indentation

The effect of partial recovery of zinc surface at room temperature after basal plane indentation was detected and studied with a scanning tunneling microscope. It was found that indentation depth recovery depending on time occurs in one stage and recovery of lateral sizes in two stages with different activation energies, which are less than that of bulk zinc self-diffusion. Possible mechanisms of surface self-diffusion of zinc atoms leading to surface crystal growth were discussed. It was shown that the dynamics of effects observed on the sample surface in the indentation area after 15-min annealing at 100°C is associated with emergence of thermally generated vacancies from the sample bulk.