Formation of E4-Centers (E c – 0.76 eV) in Gallium Arsenide

The paper deals with the effects of the bombarding-electron energy on the velocity of E4 center (E _c – 0.76 eV) formation and the temperature dependences of the efficiency of the latter in a neutral volume and the space-charge region of n–type gallium arsenide. The specimens were Schottky diodes manufactured by depositing titanium onto epitaxial layers of n-GaAs with n = (2–4)·10¹⁵ cm³. The defect concentration was obtained by the DLTS spectroscopy method. It is shown that the number of E4 centers in the total amount of irradiation-induced defects sharply increases with increasing the bombarding-electron energy from 1.3 to 2.2 MeV. It is found out that the velocity of introducing E4 centers into the space-charge region does not depend on irradiation temperature and is by far higher than that in a neutral volume. In the latter, however, this velocity is non-linearly increasing with the irradiation temperature. It is assumed that an E4 center is a complex consisting of two unit defects generated in the adjacent sites of the Ga and As sublattices through a single collision. It is noted that its final configuration is formed as a result of interaction of these defects, which depends on the dynamics of transformation of their primary charge states.     

Defects in pulsed laser and thermal processed ion implanted silicon

The evolution of the nature and concentration of the defects produced by 100 or 300 keV As ions at fluences 1 to 4×10^–12 cm^–2 inn-type, Fz Silicon doped with 10¹⁵ to 10¹⁶ cm^–3 has been studied as function of thermal treatments (in the range 500°–900 °C) and of the energy density (in the range 0.3–0.6 J cm^–2) of a light pulse from a ruby laser (15 ns, 0.69 m). Deep-level transient spectroscopy (DLTS) combined with capacitance — voltage (C-V) measurements were used to get the characteristics (energy level, crosssection for the capture of majority carriers) of the defects and theirs profiles. The difficulties encountered in the analysis of the results, due to the large compensation of free carriers in the implanted region and to the abrupt defect and free carrier profiles, are discussed in detail and the corrections to apply on the C-V characteristics and the DLTS spectra are described. The defects resulting from the two types of treatments are found to be essentially the same. Only, for laser energies higher than 0.5 J cm^–2, the laser treatment appears to introduced new defects (atE0.32 eV) which should result from a quenching process. The fact that a laser energy smaller than the threshold energy for melting and recrystallization is able to anneal, at least partially, the defects produced by the implantation, demonstrates that the annealing process induced by the laser pulse is not a purely thermal process but is enhanced by a mechanism involving ionization.     

A Bistable Defect in InP

Point defects in n-indium phosphide were studied by deep-level transient spectroscopy (DLTS). A radiation-induced bistable defect is found to form under irradiation of a space-charge region of n-InP Shottky-barrier diodes. The transformations of the defect configuration stimulated by heating, illumination, and current flow are studied.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 80–84, April, 2005.     

Restructuring of defects in silicon by action of subthreshold-energy electrons

The influence of irradiation of silicon p⁺-n diodes by 15 to 30 keV electrons on the deep level transient spectroscopy (DLTS) spectra of the diodes was studied. It was discovered that irradiation leads to the transformation of the DLTS spectra in crystals containing defect clusters. A comparison of the depth of the p-n junction in the crystal with the penetration depth of the electrons indicates that the detected rearrangement of defects is due to secondary electrons diffusing into the p-n junction. A recombination-stimulated mechanism of defect rearrangement is proposed. In crystals containing only point defects, transformation of the DLTS spectra is not observed.Deceased.Translated from Izvestia Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 32–37, June, 1990.     

Positron annihilation and Hall effect in electron irradiatedn-InP crystals

Positron annihilation and Hall effect inn-InP crystals as a function of electron irradiation up to 1 · 10¹⁹ cm^–2 and post-irradiated isochronal annealing up to 550 °C have been studied. It is concluded that in irradiatedn-InP samples positrons interact with negatively charged acceptor-type defect with level atE _c –0.33 eV, probablyV _In (primary defect). In post-irradiated isochronal annealed (up to 330 °C) samples ofn-InP positron trapping occurs preferably in secondary defects-vacancy clusters, which are formed in the temperature range (150–300 °C). Inn-InP crystals containing radiation induced defects the trapping rate was found to decrease with temperature in the range (300–77) K.     

Nuclear orientation study of the decay of204BiFe

The decay of²⁰⁴Bi nuclei (I =6⁺, T_1/2=11·22 h) oriented in an iron host was investigated on the JINR low-temperature nuclear orientation facility SPIN. The orientation parameterB ₂=1·17 (6) was obtained from the analysis of six prominent E1 gamma-transitions. From the measured normalized intensities of the gamma-rays observed some 70 values of multipole mixing ratios for the gamma-transitions in²⁰⁴Pb nucleus were determined for the first time. The spins 6, 6, 5 and 4 could be uniquely assigned to the²⁰⁴Pb negative parity levels at 3891·5 keV, 3768·4 keV, 3301·5 keV and 2338·2 keV, respectively. The spin-parity assignments of the levels at 4183·8 keV, 4094·2 keV, 3782·0 keV, 2506·9 keV and 2065·1 keV were confirmed as 6^–, 6^–, 5^–, 5^– and 5⁺, respectively. For the level at 3105·1 keV spin-parity 5^– was suggested and spinparity 7^– of the level at 2696·4 keV was called in question. The possible placements of the gammatransitions 3 1351·7 keV and 1353·4 keV in the decay scheme is discussed. The reorientation parameters for the long-living levels at 2264·2 keV (T _1/2=0·45 s) and 1273·9 keV (T _1/2= =265 ns) were determined asG ₂=0·41 (14) andG ₂=0·60 (17), respectively. For the isomeric level at 2185·7 keV (T _1/2=67·2 min) the value ofG ₂=0·88 (49) was proposed.The authors would like to express their thanks to T. I. Kracíková and M. Trhlík for the valuable discussions in the course of the evaluation of the experimental data.     

Ion beam mixing and sputtering of Kr-irradiated TiN films measured with RBS,RNRA, and PIXE

Thin titanium nitride films of 10–300 nm thickness were irradiated with ⁸⁴Kr ions of 80–700 keV energy and fluences ranging from 10¹⁶ cm² to 2×10¹⁷ cm². Sputter yields (Y=0.4–1.0) and mixing rates (k=0.05–0.5 nm⁴) were determined using the depth profiling methods RBS, RNRA, and PIXE. While the sputter yields agree well with the modified Sigmund theory, the energy dependence of the mixing rates cannot be explained by standard models.     

Thermal redistribution of boron implants in bulk silicon and SOS type structures

The redistribution of boron profiles in bulk silicon and SOS (silicon-on-sapphire) type structures is investigated in this paper. Experimental data on thermally redistributed profiles are correlated with predictions based on a computer program whose numerical algorithm was described in an earlier paper. Three cases were considered which involved the thermal redistribution of 1) a high dose (2×10¹⁵ and 5×10¹⁴ cm^–2) 80keV boron implant in (111) bulk silicon, in an oxidizing ambient of steam at 1000°, 1100°, and 1200°C, respectively; 2) a high dose (2.3×10¹⁵ cm^–2) 25 keV boron implant in (100) silicon-on-sapphire, in a nonoxidizing ambient of nitrogen at 1000 °C; and 3) a low dose (3.2×10¹² cm^–2) 150 keV boron implant in (100) bulk silicon, in oxidizing and nonoxidizing ambients that make up the fabrication schedule of an-channel enhancement mode device. For all three cases the overall correlation of computer predictions with experimental data was excellent. Correlations with experimental data based on SUPREM predictions are also included.     

Electrophysical properties of heat-treated gallium arsenide

The electrical conductivity, Hall effect, ionization energy, and defect concentration of GaAs samples subjected to various forms of heat treatment were studied. The original material comprised single crystals grown by the Bridgman and Czochralski methods with electron concentrations of 2·10¹⁵–7·10¹⁷ cm^–3. The ionization energy and defect concentration were calculated with an electronic computer. The thermal conversion of GaAs was attributed to traces of copper, lattice defects, and residual impurities. The mobility varied in a complicated manner with the temperature of heat treatment in GaAs samples retaining their original n-type conductivity.Translated from Izvestiya VU Z, Fizika, No. 3, pp. 69–76, March, 1973.     

Ion track effect on point defect production in SiC

Low-temperature (40 K) photoluminescence (PL) measurements were used to follow the defect formation induced in the 4H-SiC epitaxial layer by irradiation with 200 keV H⁺ and 800 keV C⁺ in the fluence range of 5×10⁹–3.5×10¹² ions/cm². After irradiation, the PL spectra show the formation of some sharp lines, called “alphabet lines”, located in the wavelength range of 425–443 nm, due to the recombination of excitons at structural defects induced by ion beams. The analysis of luminescence line intensity versus ion fluence allows us to mark two different groups of peaks, namely the P1 group (e, f and g lines) and the P2 group (a, b, c and d lines). The normalised yield of P1 group lines increases with ion fluence and reaches a maximum value, while the normalised yield of P2 group lines exhibits a threshold fluence and then increases until a saturation value is reached. These different trends indicate that, while the P1 group lines are related to the primary defects created by ion beams (interstitial defects, vacancies), the P2 group lines can be associated with some complex defects (divacancy, antisites). The trends are similar for irradiation with H⁺ and C⁺ ions; however, the defect formation occurs in the fluence range of 5×10⁹–10¹¹ ions/cm² for C⁺ irradiation and 10¹¹–4×10¹² ions/cm² for H⁺ irradiation. Taking into account the different values of energy deposited in elastic collision, a dependence on the ion type was found: the C⁺ ion results in being less effective in defect production as a higher defect recombination occurs inside its dense cascade.     

Electrical characterization of defects introduced in n-GaAs by alpha and beta irradiation from radionuclides

We investigated defect production in n-type GaAs with two different free-carrier densities (4×10¹⁴ and 1×10¹⁶/cm³) by using particles liberated from radionuclides. ⁹⁰Sr and ²⁴¹Am were employed as beta and alpha sources, respectively. The results obtained for electron irradiation showed that the same set of primary defects can be produced by beta irradiation from the Sr source as by electrons produced in an accelerator. Similarly, the defects produced by alpha irradiation from the Am source closely resemble those introduced by alpha irradiation in a Van de Graaff accelerator. It was found that the relative concentrations of the primary defects in electron-irradiated GaAs are different to those in alpha-particle irradiated GaAs. Further, for the first time, an alpha irradiation induced defect which seems to be related to the doping concentration was observed in the 10¹⁶/cm³ Si doped GaAs. It is concluded that the use of radionuclides is an inexpensive and convenient method to introduce and to study radiation induced defects in semiconductors.     

Change of GeSx parameters after neutron irradiation

In the paper some experimental results on the dependence of thermal conductivity, temperature conductivity coefficient, heat capacity, dc conductivity and ac conductivity on integrated neutron flux within the range from 10¹⁶ n cm^–2 to 10¹⁹ n cm^–2 are described. At integrated neutron flux of 10¹⁷ n cm^–2 an extreme in all parameters was observed. This effect can be explained by means of compensation of unsaturated bonds in the glass due to defects caused by irradiation.     

Ionic Synthesis of Ga1–x In x As Solid Solution Films

The Ga_1–x In _x As compound obtained by In-ion implantation (100 keV and (0.45–6)·10¹⁷ cm^–2) followed by thermal (800 °C and 15') or high-energy electron-beam (1 MeV, 0.6 mA·cm^–2, 660 °C, and 16 s) annealing is investigated by Rutherford backscattering, optical absorption, and capacitor photoelectromotive force. It is shown that x increases from 0.07 up to 0.21, and the band gap decreases from 1.34 down to 1.21 eV as the implantation dose increases. The surface potential decreases from 0.79 down to 0.58 V. A high efficiency of electron-beam annealing is pointed out.     

Defect study of proton-irradiated liquid-encapsulated Czochralski GaAs using the positron-annihilation technique

The positron lifetime of undoped Liquid-Encapsulated Czochralski (LEC)-GaAs and Si-doped (1.3×10¹⁸ cm^–3) LEC-GaAs was measured before and after irradiation with protons (dose 1×10¹⁵/cm², 15 MeV). In Si-doped GaAs, the decrease of positron lifetime at temperatures between 10 and 300 K are due to the decrease of the positron-diffusion length and the increase of the effective shallow traps such as antisite Ga_As. The annealing stage of the proton-irradiation-induced defects which show the different behavior from that of electron-irradiation-induced defects suggests that proton irradiation creates more complicated defect complexes, containing vacancies rather than isolated vacancy-type defects or simple complexes which have been observed during electron-irradiation processes. Above 700 K, proton-irradiation-induced defects such as vacancy-type defects and simple vacancy complexes are almost annealed out, while Si-induced defects such as Si_Ga-V_Ga complexes cannot be annealed out above 973 K.     

Magnetic moment of the 2140.2 keV 5− state in136Ba

We have determined theg-factor of the 2140.2 keV 5^– state of¹³⁶Ba using the timeintegral perturbed angular correlation (IPAC) method at an external magnetic field of 17.0 kG;g=–0.38±0.04. The half-lives of the 2140.2 keV 5^– and 2207.1 keV 6⁺ states were redetermined to be 1.5±0.1 ns and 3.1±0.1 ns, respectively. The radioactive source of¹³⁶Cs was prepared by the¹³⁸Ba(, pn) reaction.     

Dissipative flux motion in YBa2Cu3O7−δ films — Investigation by means of transport I-V curves

The nature of dissipative flux motion in epitaxial YBa₂Cu₃O_7– thin films has been investigated by means of resistivity (T, B) and transport current-voltage characteristicsE(j, T, B) covering up to 5 orders of magnitude in voltage for a wide range of temperatures (4.2–85 K) and magnetic fields (0.5–7.0 T). Activation energiesU(T, B, j) have been determined in the framework of the collective flux creep theory. It is shown thatU(T, B, j) decreases with increasing temperature, magnetic field and current density. In order to study the influence of a well-defined defect structure, columnar defects have been generated by irradiation with 340 MeV Xe-ions. From a scaling law relating theI–V curves after irradiation with the curves before irradiation it is found that vortices pinned by the columnar defects do not contribute to dissipation. Due to irradiation the irreversibility line is shifted to higher magnetic fields, indicating its connection to the pinning mechanisms present in the samples.     

Correlation of charge trapping and electroluminescence in highly efficient Si-based light emitters

In this paper we report on recent results on charge trapping and electroluminescence (EL) from Ge rich SiO₂ layers. Thermally grown 80 nm thick SiO₂ layers were implanted with Ge ions at energies of 30–50 keV to peak concentrations of 1–6 at%. Subsequently rapid thermal annealing was performed at 1000°C for 6, 30 and 150 s under a nitrogen atmosphere in order to form luminescence centers. A combination of capacitance–voltage (CV) and current–voltage (IV) methods was used for the investigation of the trapping properties. It was found that at electric fields <8 MV/cm electron trapping dominates while at higher electric fields which are typically required for the EL operation of the devices positive charge trapping occurs. It is assumed, that the trapping sites which are responsible for the trapping of the positive charge are in strong relation to the defects causing the luminescence.     

Spatial distribution, build-up, and annealing of radiation defects in silicon implanted by high-energy krypton and xenon ions

An x-ray diffraction study of defect formation in silicon irradiated by Kr⁺ (210 MeV, 8×10¹²−3×10¹⁴ cm⁻²) and Xe⁺ (5.6 BeV, 5×10¹¹−5×10¹³ cm⁻²) ions is reported. It has been established that irradiation produces a defect structure in the bulk of silicon, which consists of ion tracks whose density of material is lower than that of the host. The specific features of defect formation are discussed taking into account the channeling of part of the ions along the previously formed tracks and the dominant role of electron losses suffered by the high-energy ions. It is shown that the efficiency of incorporation of stable defects by irradiation with high-energy ions is lower than that reached by implanting medium-mass ions with energies of a few hundred keV. Fiz. Tverd. Tela (St. Petersburg) 40, 1627–1630 (September 1998)     

Photoluminescence detection of impurities introduced in silicon by dry etching processes

We report on a photoluminescence study of silicon samples subjected to different dry etching processes. Several luminescence lines, known from defects produced by high-energy irradiation, manifest damage of the crystalline material. Noble gas ion beam etching (using Ne⁺, Ar⁺, Kr⁺, and Xe⁺) with ion energies as low as 400 eV produces characteristic luminescence lines which correspond to defects within a 200–300 Å thick surface layer. Incorporation of carbon during CF₄ reactive ion etching produces the familiar G-line defect. The G-line photoluminescence intensity in our samples is directly correlated with the substitutional carbon concentration, as determined by infrared absorption measurements before the etch process; we therefore suggest that a simple method to determine the substitutional carbon concentration in a crystalline silicon sample is a standard dry etching process and a comparison of the resulting G-line photoluminescence intensity to a calibrated sample. The sensitivity of this method seems to be better than 10¹⁴ carbon atoms/cm³.     

Effect of electron irradiation on the properties of germanium-doped gallium arsenide

The Hall effect, electrical conductivity (77–370 K), and photoluminescence spectra (77 K) are studied in single-crystals of nuclearly doped GaAs (NDG) and GaAs doped with Ge by the metallurgical method after irradiation by electrons (E= 1 MeV, D=1.1·10¹⁵–3.8·10¹⁸ cm^–2). Initial electron concentrations were n= 1.7·10¹⁷ cm^–3 and n₀=2.6·10¹⁷ cm^–3 respectively. In the GaAs doped during crystal growth by the Czochralski method the degree of compensation related to the amphoteric impurity Ge is higher (K=0.8) than in the NDG (K=0.4) for identical initial electron concentration. It was established that the rate of charge carrier removal in GaAs is lower than in NDG, while radiation defects are more thermostable in NDG. The energy spectrum of radiation defects and radiating recombination centers, and the basic steps in reestablishment of electrophysical and optical properties in GaAs and NDG are similar, i.e., they do not depend on the method of germanium doping.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 82–86, April, 1991.