G. Myburg

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.

Summary of Schottky barrier height data on epitaxially grown n- and p-GaAs

The Schottky barrier height values, as determined by the current‐voltage and capacitance ‐voltage techniques, of 43 metals which were fabricated by following the same cleaning procedure and using the same high-quality organometallic vapour phase epitaxially (OMVPE) grown (100) n-type GaAs material and 13 metals on molecular beam epitaxially grown (MBE) p-GaAs, are presented. Of all the metals involved in this study, Ga had the lowest mean Schottky barrier height of about 0.60 eV on n-GaAs and the highest on p-GaAs of 0.83 eV. Cu, Ag, Pt and Sb had the highest barrier heights of about 1 eV on n-GaAs. It was found that there exists no linear relationship between Schottky barrier height and metal work function as is suggested by the Schottky‐Mott theory, if all 43 metals are taken into account. Similar results were obtained if the metal work function was replaced by the Pauling or Miedema electronegativities. In contrast with this, if only a selected group of metals is chosen and more specifically those with the higher melting points which were deposited by means of an electron gun, an approximately linear tendency does exist between Schottky barrier height and metal work function. From this linear dependency, the density of states was determined to be about 6 〈 10 13 /eV per cm 2 and the average pinning position of the Fermi level as 0.55 eV below the conduction band.

Accumulation of radioactive corrosion products on steel surfaces of VVER type nuclear reactors. I. 110mAg

Formation, presence and deposition of corrosion product radionuclides (such as 60 Co, 51 Cr, 54 Mn, 59 Fe and/or 110m Ag) in the primary circuits of water-cooled nuclear reactors (PWRs) throw many obstacles in the way of normal operation. During the course of the work presented in this series, accumulations of such radionuclides have been studied at austenitic stainless steel type 08X18H10T (GOST 5632-61) surfaces (this austenitic stainless steel corresponds to AISI 321). Comparative experiments have been performed on magnetite-covered carbon steel (both materials are frequently used in some Soviet VVER type PWRs). For these laboratory-scale investigations a combination of the in situ radiotracer ‘thin gap’ method and voltammetry is considered to be a powerful tool due to its high sensitivity towards the detection of the submonolayer coverages of corrosion product radionuclides. An independent technique (XPS) is also used to characterize the depth distribution and chemical state of various contaminants in the passive layer formed on austenitic stainless steel. In the first part of the series the accumulation of 110m Ag has been investigated. Potential dependent sorption of Ag a ions (cementation) is found to be the predominant process on austenitic steel, while in the case of magnetite-covered carbon steel the silver species are mainly depleted in the form of Ag2O. The XPS depth profile of Ag gives an evidence about the embedding of metallic silver into the entire passive layer of the austenitic stainless steel studied. ” 1999 Elsevier Science B.V. All rights reserved.

ELECTRICAL CHARACTERIZATION OF DEFECTS INTRODUCED IN P-SI1-XGEX DURING ELECTRON-BEAM DEPOSITION OF SC SCHOTTKY BARRIER DIODES

Scandium (Sc) Schottky barrier diodes were fabricated by electron-beam (EB) deposition on epitaxially grown p-Si1−xGex strained films with x=0.0–0.2. The EB deposition was performed either with or without shielding the Si1−xGex samples. The barrier height and the defects introduced during EB deposition have been investigated as a function of Ge composition. Our results showed that the barrier height decreased as the band gap changed with increasing Ge content. The defect properties were studied with deep-level transient spectroscopy. The most prominent defect observed in p-Si was a hole trap H(0.53) at Eν+0.53 eV. Increasing the Ge content led to a decrease in the activation energy of this defect and this decrease followed the same trend as the band-gap variation, suggesting that the main defect detected in p-Si1−xGex is the same as that observed in p-Si.

A deep level transient spectroscopy characterization of defects induced in epitaxially grown n-Si by low-energy He-ion bombardment

Epitaxially grown n-Si was bombarded with low-energy (1 keV) He ions. Deep level transient spectroscopy revealed that this introduced four prominent defects with energy levels at 0.14, 0.20, 0.30, and 0.55 eV, respectively, below the conduction band. The electronic properties and annealing behavior of these defects are different to those of the main defects, namely, divacancies (V2) and vacancy-phosphorous centers, observed after 5.4 MeV He-ion bombardment of the same material. We propose that, except for the defect with an energy level at Ec−0.14 eV, the defects introduced by 1 keV He-ion bombardment of n-Si may be related to: (1) vacancy clusters larger than divacancies, or (2) incorporation of He and H into V2 or higher-order vacancy clusters.

Electronic and annealing properties of a metastable He-ion implantation induced defect in GaAs

Abstract We have investigated, using DLTS, the properties of electrically active defects introduced in undoped and Si-doped epitaxially grown n-GaAs implanted with He-ions. Particular attention was paid to the introduction kinetics of the metastable Eα3 defect. We have found that Eα3 is not introduced during implantation, as previously believed, but thereafter upon annealing above 285 K. Its introduction is governed by first order kinetics and we suggest that it is formed as the result of larger irradiation induced clusters disintegrating. The concentration of Eα3 and the temperature range in which its metastable transformations occur, imply that it may play an important role in reversibly altering the free carrier concentration of ion-implanted GaAs.

Electrical characteristics of neutron irradiation induced defects in n-GaAs

Abstract Palladium Schottky barrier diodes (SBDs) on epitaxially grown n-GaAs were irradiated with neutrons from a reactor and a p(66)/Be (40) clinical source. From current-voltage (I–V) and capacitance-voltage (C–V) measurements it was found that neutron irradiation caused generation-recombination currents and resulted in a reduction in the free carrier concentrations of the epitaxial layers. A linear relation was found between the irradiation fluence, the free carrier removal and the reverse leakage current of neutron irradiated SBDs. Deep level transient spectroscopy (DLTS) indicated that five electron traps, Enl-En5, were introduced during neutron irradiation. These defects are shown to be responsible for the degradation of neutron irradiated SBDs.

Simultaneous Observation of Sub- and Above Threshold Electron Irradiation Induced Defects in GaAs

Sub- and above threshold defects were introduced in n-type OMVPE grown GaAs during 3 keV and 3 MeV electron irradiation, respectively. The electrical properties of these defects were determined by DLTS measurements in samples that contained subthreshold defects only, above threshold defects only, as well as samples that contained both types of defects. A careful examination of the low temperature DLTS peaks revealed that although the sub- and above threshold defects have similar properties, they are nevertheless distinguishable from each other and are therefore not the same as has previously been speculated.

Defect annealing of alpha-particle irradiated n-GaAs

The annealing behaviour of irradiation induced defects in n-type GaAs irradiated at 300 K with 5.4 MeV alpha-particles from an americium-241 (Am-241) radio nuclide have been investigated. The annealing kinetics are presented for the alpha-particle induced defects Eα1–Eα5 detected in Organo-Metallic Vapor Phase Epitaxially (OMVPE) grown n-GaAs doped with silicon to 1.2×1016 cm−3, these kinetics are compared to those obtained for similar defects (E1–E5) detected after electron irradiation. While defects Pα1 and Pα2 were detected after removal of the electron defects Eα4 and Eα5, respectively, a new defect labelled Pα0, located 0.152 eV below the conduction band, was introduced by annealing. The thermal behaviour and trap characteristics of these three defects (Pα0–Pα2) are presented. In an attempt to further characterise defects Pα0 and Pα1 a preiliminary study investigating the emission rate field dependence of these defects was conducted, it was observed that defect Pα0 exhibited a fairly strong field dependence while Pα1 exhibited a much weaker dependence.

Electronic properties of defects introduced in strained, epitaxial p-type SiGe alloys during sputter etching in an argon plasma

We have used deep-level transient spectroscopy in an investigation of the electronic properties of defects introduced in boron-doped, strained p-type Si1-xGex alloys with x = 0 and 0.05, during argon plasma sputter etching. These defects are compared with those introduced during electron beam deposition of metal contacts and after 5.4 MeV particle irradiation. Four defects with discrete energy levels, ranging from 0.22 eV to 0.55 eV above the valence band, were introduced in p-Si during sputtering. The most prominent defect, detected in Ar plasma etched samples, has similar electronic properties to those of the defects detected after electron and particle irradiation. The main defects detected in p-Si were also observed in p-Si0.95Ge0.05. One of the dominating peaks has been correlated with the interstitial carbon-interstitial oxygen pair. The decrease in activation energy of this defect with increasing Ge content from x = 0 to 0.05 is found to follow the same variation as the bandgap of strained Si1-xGex/Si. The energy level position of the defect, relative to the conduction band, is therefore the same for x = 0 and 0.05 indicating that such a level is pinned to the conduction band.