Results are reported of a Deep Level Transient Spectroscopy (DLTS) study of the conversion of the divacancy, with energy level at Ev+0.19eV, to a level at Ev+0.24eV after anneal at temperatures below its dissociation temperature (300°C). In literature both levels have been associated with the donor level of the divacancy.

Diodes processed on p-type Float Zone (FZ) and Czochralski (Cz) silicon wafers with boron concentration between 0.2 and 3E15 cm−3 are irradiated with 2 MeV electrons. Before and after anneal (200°C and 250°C) DLTS spectra are recorded to get a full electrical characterisation of the induced defects.

The observed conversion is proposed to be a gradual transformation of the divacancy to a divacancy-oxygen complex.

We have found that the measured diffusivity can be quite different than predicted by recent models of multiply-charged defects. Key problems dealing with the measurement and the interpretation of diffusion mechanisms are discussed. Using a few common variations in GaAs epilayer growth, we have obtained diffusivities which range over several orders of magnitude at the same temperature. Making use of the relatively weak In-As bond, we have used In as a marker to measure group III interdiffusion, DIII. DIII is consistent with the results of others using Al as a marker in n-type GaAs, but orders of magnitude smaller than predicted by the triply charged Ga vacancy, V3−Ga, model of Tan and Gosele. Although diffusion can be attributed to a negatively charged vacancy in n-type GaAs, In is found to often move by a kick-out mechanism in p-type GaAs. It appears likely that many early experiments with n- and p-type GaAs-AlAs interdiffusion were affected by large concentrations of Ga interstitials, IGa, caused by Fermi energy pinning at the growing surface. We present the first direct experimental evidence for the existence of a positively charged Ga interstitial. Our results, combined with those of others, suggest that VGa has a single negative charge associated with it. Because epilayer growth conditions appear to cause the point defect concentrations to deviate substantially from equilibrium, we conclude that the exact charge states of VGa and IGa still remain to be determined.

The creation of negative-U defects (NUD) is a spin-dependent process, that could be used for getting information about NUD themselves; and the NUD destruction is accompanied by the Coulomb’s repulsion between charge carriers.

We report observations on the effects of rapid thermal annealing on oxygen and carbon content of different single and multicrystalline silicon materials.

From the comparison between the resulting effects of conventional and short thermal annealing, we can deduce that the increase of the concentration of interstitial oxygen after a rapid thermal annealing (RTA) is due to the dissociation of some microprecipitates in silicon, which is significantly affected by the initial oxygen content, thermal history, defects and impurity content such as carbon.

In order to investigate the basic properties of radiation-induced defects in ZnO crystals, positron annihilation lifetime and Doppler-broadening measurements were performed on crystals sinterd for 18 hours at 1200 °C and irradiated with 3 MeV protons at 223 K. The irradiation induced a colour change of the specimens from the original yellowish-white to dark orange or even brown. Isochronal annealing experiments showed three annealing stages, centred at about 150 °C, 500 – 550 °C, and 750 °C, respectively. These stages are related to the annealing of variously sized vacancy complexes.

Since the first report by our group in 1992, iron-related defects in n-type silicon has been found to exhibit unusual in-diffusion and annealing properties. We review in this paper the recent progress in understanding the electrical and diffusion properties of iron-related defects in n-type silicon. We have shown from DLTS and Hall effect that iron in n-type silicon is electrically ionized and introduce one donor level at Ec-0.41 eV (level C) and, at least, one acceptor level at Ec-0.21 eV (level B). The donor character of former level has been confirmed by a Poole-Frenkel effect. The concentrations of two centers introduced are in the order of 1013 cm−3 at maxima. In-diffusion behavior of levels B and C show that these levels are intermediate states in a consecutive reaction of iron-related complex formation. Low-temperature isothermal annealing experiments from the room temperature to 200°C suggest that iron-related donor is formed, in part, by the electrostatic attractive force between two point charges.

Temperature-dependent (80 … 300 K) measurements of dislocation recombination activity by the electron-beam-induced-current (EBIC) technique are reported. Controlled Cu contamination (ppb to ppm range), chemomechanical polishing and hydrogenation treatments were applied to alter dislocation properties. Increasing Cu level is found not only to increase the electrical activity of misfit dislocations in SiGe/Si structures at 300 K, but also to change its dependence on temperature. At low contamination, shallow centres control dislocation activity while deep centres are characteristic at higher Cu levels. Heavy Cu contamination results in very strong recombination activity which is attributed to precipitates. Chemomechanical polishing has an effect which is analogous to medium Cu contamination. Hydrogenation was found to passivate recombination activity at 300 K, but did not show pronounced effects on activity at low temperature.

We have characterised the recombination at Oxidation Induced Stacking Faults (OISF) by employing a combination of DLTS and Minority Carrier Transient Spectroscopy (MCTS). The recombination rate at traps associated with the OISF has been compared with recombination at a conventional point defect also present in the silicon. We find that the effect of small amounts of decoration by copper is to increase hole capture rates at electron filled traps. Infra Red Beam Induced Current measurements are consistent with this in that they also indicate that decoration causes enhanced recombination at the extended defects.

Metal-semiconductor-metal photodetectors fabricated using low-temperature-grown GaAs have been passivated using AlGaAs cap layers in order to understand the influence of surface states and fields on the properties of these detectors. It has been found that passivation has little effect on the time response or persistent photoconductive tails associated with the detectors, but that responsivity and dark current can be enhanced in certain circumstances. The dependence of the temporal response on optical fluence and dc-voltage bias were observed for both passivated and unpassivated detectors.

We report on the optical characterization of sulphur (S) passivated AlxGa1−xAs/GaAs surfaces using photoluminescence (PL) and surface photovoltage (SPV) measurements. Both techniques show an enhancement in the near bandgap signal intensity, implying a reduction of the non-radiative recombination rate at the surface. To counter the instability of S-passivation, due to re-oxidation, dielectric layers of silicon nitride were deposited using electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD); the deposition of dielectric layers up to lOOnm thick does not appear to cause significant deterioration or stress at the insulator/AlGaAs interface. The dielectric layers are shown to be resistant to oxidation, and effective in maintaining the passivation effect over a period of weeks.

We report for the first time a successful application of semi-insulating amorphous GaAs layer for surface passivation of index-guided vertical-cavity surface-emitting lasers. The amorphous GaAs layers on ion-beam-etched active region and mirror layers provide a significant improvement, more than 20%, in the threshold current density and differential quantum efficiency. The improvement of these performances is attributed to low defect density at the surface of active layers induced by amorphous GaAs.

A new approach to GaAs surface passivation is suggested which consists in the treatment of GaAs in sulfide solutions in which different alcohols are used as solvents. It has been found that the photoluminescence efficiency of sulfide-treated GaAs associates with the dielectric constant of the solvent being used. With the decrease of dielectric constant value the PL intensity of sulfidized GaAs increases. Sulfidizing in isopropanol-, butanol- or t-butanol-based solutions leads to the formation of sulfide coat which PL properties remain constant even after strong laser irradiation. The effect of the solvent on the GaAs PL efficiensy is explained whithin the framework of hard and soft acids and bases. Thus the use of alcohol-based sulfide solution with low dielectric constant value greatly reduces surface recombination losses in sulfide-treated GaAs.

Ta2O5-based composite films prepared by magnetron sputtering have been investigated with respect to their dielectric properties. As additive third oxides, Y2O3 and WO3 were found to be effective in improving insulating properties without decreasing their dielectric constant. Furthermore, electrical properties of Ta2O5-Y2O3 films were investigated by measuring the current-voltage characteristics in the temperature range from 100 to 330 K. Measurement of temperature dependence of the leakage current revealed that the conduction mechanism at RT changed from the Poole-Frenkel type to the Fowler-Nordheim tunneling type by adding Y2O3 into Ta2O5. Based on the detailed analysis of the results, it is concluded that the addition of Y2O3 into the Ta2O5 film is effective in the reduction of defect density without high-temperature annealing and the alteration of electrical conduction mechanisms of the films.

We generate liquid and amorphous Si1_xGex alloys for various Ge compositions using ab initio molecular dynamics approach. The electronic bonding characters and structural properties are discussed in terms of radial distribution function, bond angle distribution, and order parameters. Although the order parameters suggest approximately random alloy for all compositions, the snapshots reveal clearly phase separation. We will discuss how the phase can be separated in SiGe alloy system.

Hydrogen incorporation in ECR-CVD silicon oxynitride films deposited using tris dimemylaminosilane (TDAS) as the silicon precursor was investigated. The as-deposited silicon dioxide films were shown to contain little hydrogen (<2%) as determined by both FTTR and nuclear reaction analysis (15N profiling). Films were obtained with high breakdown fields (>10 MV/cm) and low interface state densities (2×l011cm−2) on silicon without special surface preparation. Silicon nitride films were found to contain large hydrogen concentrations, both bonded and unbonded, which evolved from the film due to beam irradiation during 15N profiling. We were able to demonstrate that dilution of the nitrogen plasma with both hydrogen and argon was effective in avoiding problems of trace oxygen contamination and poor film adhesion, and reducing the hydrogen concentration in the nitride films.