Interstitial Related Defects Research Articles

Modelling of interstitial-related defects in diamond

Abstract Radiation damage in diamond is a major experimental research tool and is becoming a technologically important topic. Although the vacancy and its complexes are well understood, the other products, the interstitials, are much less studied. Recent theoretical modelling of defects in diamond has assisted in the identification of several structures and processes. The nitrogen interstitial has been established as having a buckled bond-centred structure, with the splitting of local modes under isotope substitution that is observed. It has a metastable structure that is more stable in the negative charge state, which helps to explain the anomalous annealing data. The models of the self-interstitial agree that it has a (001) split structure. However, here, it is difficult to identify the experimental data with the defect. A brief review of the experimental data along with the theoretical models leads to the conclusion that the R2 centre, seen in electron paramagnetic resonance (EPR), may derive from the split interstitial. The 5RL optical centre and the 1570 cm −1 infra-red absorption have vibrational modes of similar energies to those of the split interstitial, but the high annealing temperatures imply that the interstitial is trapped in these centres.

Hydrogen interaction with implantation induced point defects in p-type silicon

Interaction of hydrogen with implantation induced point defects in p-type Si has been monitored using deep level transient spectroscopy. H ions are implanted into p-Si using low doses in the range from 109 to 1010 cm−2. Vacancy and interstitial related defects are observed. Besides irradiation induced defects with levels at Ev+0.19 and Ev+0.35 eV, two additional defect levels at 0.28 and 0.51 eV above the valence band edge (Ev) are resolved. They are identified as hydrogen related after comparison with He, B, and C implanted p-type Si. The generation of these defect levels, in the presence of hydrogen, has been studied as a function of ion dose, sample depth, and impurity content in the as grown Si. The level at Ev+0.19 eV shows a saturation effect for higher hydrogen doses. This is attributed to passivation by mobile hydrogen through the formation of neutral complexes. The level at Ev+0.51 eV has been assigned to be a complex involving H and B interstitials.

Thermal Annealing Recovery of Intersubband Transition in Proton-Irradiated GaAs/Al0.3Ga0.7As Multiple Quantum Wells

AbstractOptical absorption spectra of intersubband transitions in heavily proton irradiated n-type GaAs/AlGaAs multiple quantum wells were studied as a function of isochronal and isothermal annealing. The absorption spectra of intersubband transitions were depleted in samples irradiated with 1MeV proton doses higher than 1.0 × 1014 cm−2. Thermal annealing of the irradiated samples show that the intersubband transitions are recovered. The relatively lower annealing temperatures at which the recovery is observed indicate that the irradiation-induced defects that trapped the two-dimensional electron gas in the quantum wells are vacancy and interstitial related defects. Once these traps are thermally annealed the electrons are released back to the quantum wells, resulting in the recovery of the intersubband transitions.

Electrical characterization of MeV heavy-ion-induced damage in silicon: Evidence for defect migration and clustering

We have studied electrical activity of defects created by high-dose MeV heavy-ion implantation in n-silicon. Heavy damage induced by Ar+ and Au+ ions is embedded within depletion layers of Schottky diodes. The defects are characterized using capacitance–voltage (C–V), current–voltage (I–V), deep-level transient spectroscopy (DLTS) and time analyzed transient spectroscopy techniques. Large concentration of defects in the depletion layer of as-implanted device lead to unusual features in C–V and I–V characteristics. The damage layer is found to extend several microns beyond the ion range or the damage profile predicted by standard Monte Carlo simulation packages. The dominance of a single trap in the damaged region is established from hysteresis effect in C–V, space-charge-limited conduction in forward I–V and DLTS spectrum. With annealing in the temperature range of 400–600 °C, the observed changes in the defect profile indicate that the effective electrical interface between damaged and undamaged layer moves progressively towards the surface. From transient spectroscopic analysis the major defect is found to be a midgap trap whose energy is sensitive to the degree of disorder in the damaged layer. The experimental features in C–V characteristics have been simulated using model charge profiles taking into account crossing of the Fermi level with the midgap trap within the depletion layer. The simulations suggest the presence of a compensated region and a sharp negatively charged defect profile at a distance much larger than that expected from ion range. Our results constitute experimental evidence, in qualitative agreement with recent predictions of molecular dynamics simulations, of defect migration and clustering of interstitial related defects even at room temperature in the case of high-dose irradiation.

Ion Implantation-Induced Defects and the Influence of Titanium Silicidation

AbstractThermal evolution of ion implantation-induced defects and the influence of concurrent titanium silicidation in pre-amorphized p-type Si (implanted with 25 KeV, 1016 cm2Si+) under rapid thermal processing (RTP) have been investigated. Presence of implantation-induced electrically active defects has been confirmed by current-voltage (IV) and deep level transient spectroscopy (DLTS) measurements. DLTS characterization results show that the evolution of electrically active defects in the Si implanted samples under RTP depend critically on the RTP temperature: Hole traps HI (0.33 eV) and H4 (0.47 eV) appear after the highest temperature (950 °C) anneal, while a single trap H3 (0.26 eV) shows up at lower anneal temperatures (≤ 900 °C). The thermal signature of H4 defect is very similar to that of the iron interstitial while those of HI and H3 levels appear to originate from some interstitial-related defects, possibly complexes. A most interesting finding is that the above interstitial related defects can be eliminated completely with Ti silicidation, apparently a result of vacancy injection. However the silicidation process itself introduces a new H2 (0.30 eV) level, albeit at much lower concentration. This same H2 level is also seen in unimplanted samples under RTP. The paper will present details of defect evolution under various conditions of RTP for samples with and without the self-implantation and silicidation.

Evidence of Defect Migration and Clustering in MeV Heavy Ion Damaged Silicon

AbstractWe have studied electrically active defects created by MeV heavy ion implantation in n-silicon. The buried damaged layer, created by implanting Ar’ ions of energy 1.45 MeV and doses in the range 1013-1014 cm−2 at room temperature, is embedded within the depletion layer of a Schottky diode. The defects are characterized using capacitance-voltage (C-V), current-voltage (I-V) and deep level transient spectroscopy (DLTS). Large concentration of electrically active defects are found to occur in a region several microns beyond the ion range or the damage profile predicted by Monte Carlo simulations. The dominance of a single trap in the damaged region is established from hysteresis effect in C-V, space charge limited conduction in forward I-V characteristics and DLTS results. With annealing in the temperature range of 400-600C, the observed changes in defect charge profile indicate that the effective electrical interface moves progressively towards the surface. C-V characteristics have been simulated using model charge profiles which suggest presence of a compensated region and a sharp negatively charged defect profile at a distance much larger than that expected from ion range. Our results constitute experimental evidence of migration and clustering of interstitial related defects, even at room temperature in case of high dose irradiation.

Photoluminescence spectroscopic investigation on the quality of diamond films grown in oxy-acetylene combustion flame

Polycrystalline diamond films were deposited on (100) silicon substrates at 700 °C by oxy-acetylene combustion flame operated under near neutral (C 2H 2/O 2∼1.0) condition in the open atmosphere. The thickness profile, nucleation density, surface morphology, and microstructure of the diamond films were analysed using surfometry, optical microscopy, X-ray diffraction and scanning and transmission electron microscopy. Photoluminescence (PL) spectroscopy (380 to 680 nm spectral range) was used for studying the distributions of crystalline defects and impurities at different growth regions along the radius of the circular (5–6 mm diameter) films. The film deposited from acetylene feather showed structural and crystalline inhomegeneities. The PL spectra originated from the centre of the growth region indicated a broad bright-blue luminescence band (around 2.81 eV). This bright-blue luminescence band appeared owing to the recombination of trapped electrons at the donor states with holes in the valence band. Substitutional nitrogen incorporated during film growth from open atmosphere possibly created deep donor states. The spectra recorded from the edge of the growth region of the same film exhibited some structural features (other than 2.81 eV) at 2.16, 2.34, (2.63 and 2.75), (3.10 and 3.19) eV. The prominent appearance of such PL emission bands from the optical centres involving isolated nitrogen–carbon vacancy, carbon interstitials and nitrogen–carbon interstitial related defects respectively, indicated that defect/impurity incorporations at the edge of the deposit were higher than the centre of the deposit. The radial gradient of substrate temperature and the non-uniform distribution of flame species/impurities were mainly responsible for such structural inhomogeneities. However, the PL spectra of diamond films deposited by the periodic exposure into feather and outer zone of the flame with time period ( t D: t E=12 s: 3 s) ratio, exhibited the bright-blue luminescence band (around 2.81 eV) and a broad pink luminescence band centred around 2.16 eV. The structure around 2.16 eV was believed to be originated from the nano crystalline diamonds precipitated in the carbon matrix. The PL emission feature was found identical through out the growth region for this film. It is concluded that the thermal recycling to the growing films minimized the structural inhomogeneities. © 1997 Elsevier Science S.A. All rights reserved.

A study of the configurations of boron in silicon using an empirical approach

The configuration space of boron in silicon has been investigated using an empirical potential approach. This study indicates that energetically favourable configurations consist of a number of three-fold coordinated split interstitials. A configuration consisting of a four-fold boron-interstitial in combination with a two-fold silicon is found to be perfectly aligned in the <111> direction. This configuration in the positive charge state is a possibility for the boron interstitial related defect found via EPR and DLTS.

Interstitial related defect of12B implanted into n- and p-type silicon

β-radiation detected nuclear magnetic resonance (β-NMR) measurements of12B occupying sites with noncubic surroundings after implantation into Si have been extended from p-type to moderately doped n-type material. The quadrupole split signals observed in both materials indicate the existence of the same interstitial related boron defect but with lower thermal stability in n-type Si.

EPR evidence for As interstitial-related defects in semi-insulating GaAs.

We report the analysis of the residual paramagnetic structure appearing in semi-insulating GaAs after microwave saturation of the ${\mathrm{As}}_{\mathrm{Ga}}$-related spectrum and most intense after preliminary plastic deformation of the material. It is separable into two similar and correlated central hyperfine partially resolved spectra of trigonal symmetry, both attributed to As interstitial-related defects. Some possibilities of suitable complexes, especially in the recent context of the EL2 identification with an ${\mathrm{As}}_{\mathrm{Ga}}^{+}$-${\mathrm{As}}_{\mathit{i}}$ pair, are discussed.

New defect states in irradiated p-type silicon

DLTS measurements are used to detect two new defect states in irradiated p-type silicon. The amplitude and the rate of annealing of the E(0.39) state depende on the minority carrier injection level. It is supposed that the E(0.39) trap is a silicon interstitial related defect because the annealing of this state enhanced the concentration of interstitial carbon. The other new defect H(0.35) is identified as a metastable precursor to the C iO iH(0.38) center. An energy barrier of 1 eV separates the MH(0.35) state from the stable C iO i configuration.

Identification of Interstitial Carbon Related Defects in Silicon

ABSTRACTDLTS measurements are used to detect and identify the interstitial related defects in n-type silicon. The materials dependences of the reactions of the [E(0.12), H(O.27)], [ME(0.30), ME(0.29), ME(0.23), ME(0.21)], ]ME(0.10), ME(0.17)] and [H(0.36)] spectral features lead to their identification as representing the two charge states of Ci, the multistable configurations of Ps-Ci, the bistable Cs-Sii-Cs, and the Ci-Oi defects, respectively. The branching ratios for the reactions of interstitial carbon with the impurities are given.

Characterization of the grown-in defects in Zn-doped InP

Studies of the effect of low temperature thermal annealing (170 °C) and laser annealing on grown-in defects in LEC grown Zn-doped InP have been made using the DLTS technique. One hole trap with energy of E v+∅.52 eV and density of 1.8×10∅ 15 cm −3 was observed in these InP samples. The potential well for this hole trap was determined by comparing the calculated field dependent emission rates with the field enhanced emission rate data obtained from the DLTS measurements. The results show that the potential well for this hole trap may be due to either a Dirac well or a square well, and hence the physical origin for this hole trap is attributed to either a phosphorus vacancy or a phosphorus interstitial related defect.

Photodegradation in silicon

The state of knowledge concerning the following defects in silicon is briefly surveyed: substitutional impurities; vacancy-related defects; interstitial-related defects; defect pairs. Although a great deal is known, it is argued that not enough is yet known to model radiation damage production in the bulk or in the vicinity of the junction of a solar cell. The results on photon degradation (and enhancement) of solar cells are then reviewed, and it is suggested that defect pairs may be the defects responsible. Mechanisms for photon-induced dissociation of pairs are discussed but a more detailed understanding awaits the identification of the actual defects.