Paul Clauws

Oxygen related defects in germanium.

Spectroscopic investigations during the last decade have resulted in a detailed picture of oxygen related defects in germanium such as oxygen interstitials and thermal donors. The results are summarized and compared with those of equivalent centres in silicon. The many similarities suggest that unified models for the major oxygen defects in the two semiconductors may apply.

Low‐temperature anneal of the divacancy in p‐type silicon: A transformation from V2 to VxOy complexes?

Deep level transient spectroscopy of electron irradiated p‐type silicon reveals a defect level at Ev+0.19 eV, which during anneal treatments at 200 °C gradually transforms into a band with Ev+0.24 eV. Both energy levels however, are reported in literature to be the donor level of the divacancy. In the present study it is proposed that during the low‐temperature anneal the divacancy interacts with oxygen, forming a V2O complex. During heat treatments at temperatures in the range between 250 and 450 °C a further shift of the deep level to higher energy positions is observed which might be related with other vacancy‐oxygen complexes.

Tin doping of silicon for controlling oxygen precipitation and radiation hardness

This paper reviews the impact of doping silicon with substitutional tin impurities on the formation of intrinsic and extrinsic lattice defects. The two major topics covered are (i) the effect on the diffusivity and aggregation/precipitation of interstitial oxygen in Czochralski (CZ) silicon and (ii) the formation of stable radiation defects in irradiated Sn-doped material. As demonstrated, the compressive stress associated with incorporating a large Sn atom on a lattice site is the basic feature governing the interactions with point defects. Consequently, Sn acts as a selective vacancy trap, while, in contrast, not affecting interstitial reactions. This leads to a reduced formation of oxygen thermal donors in n-type Si and lowers the concentration of vacancy-oxygen and divacancy centers in irradiated material. Enhanced oxygen precipitation has been noted around 750°C in p-type CZ silicon. Furthermore, specific Sn-related radiation defects are introduced, which question the use of doping with tin as a technique for substrate hardening.

DLTS and admittance measurements on CdS/CdTe solar cells

Abstract Deep level states can affect the characteristics of thin film solar cells both by their charge and by their recombination. Hence, full solar cell characterisation should include deep states. Deep level transient spectroscopy (DLTS) and admittance spectroscopy (AS) measurements ( Y ( f , T )) have been made on a series of CdTe/CdS thin film solar cells. Majority and minority trap DLTS was performed between 5 and 330 K revealing semi-shallow to mid-gap traps, depending on the sample. The DLTS results are compared with those of AS in the 100–320 K range at frequencies from 100 Hz to 1 MHz. The energy range probed with the AS is narrower than that of the DLTS method. Both methods give comparable results in the energy range where they overlap. The results are compared with literature data. The difference between cells which received a CdCl 2 treatment in air and those which received the treatment in vacuum is discussed.

Germanium content dependence of radiation damage in strained Si/sub 1-x/Ge/sub x/ epitaxial devices

The irradiation damage in n/sup +/-Si/p/sup +/-Si/sub 1-x/Ge/sub x/ epitaxial diodes and n/sup +/-Si/p/sup +/-Si/sub 1-x/Ge/sub x//n-Si epitaxial heterojunction bipolar transistors (HBTs) by fast neutrons and MeV electrons is studied as a function of fluence and germanium content for the first time. The degradation of the electrical performance of both diodes and HBTs by irradiation increases with increasing fluence, while it decreases with increasing germanium content. The damage coefficient of reverse current for x=0.12 and 0.16 diodes irradiated by neutrons is calculated to be 6.2/spl times/10/sup -21/ and 5.5/spl times/10/sup -21/ n/sup -1/ A cm/sup 2/, respectively. That of h/sub FE/ for electron-irradiated x=0.08, 0.12 and 0.16 HBTs is 7.6/spl times/10/sup -16/, 2.7/spl times/10/sup -16/ and 1.6/spl times/10/sup -16/ s/sup -1/ cm/sup 2/ respectively. >

Oxide phase determination in silicon using infrared spectroscopy and transmission electron microscopy techniques

Infrared absorption spectra of polyhedral and platelet oxygen precipitates in silicon are analyzed using a modified Day–Thorpe approach [J. Phys.: Condens. Matter 11, 2551 (1999)]. The aspect ratio of the precipitates is determined by transmission electron microscopy analysis. The reduced spectral function and the stoichiometry of the precipitate are extracted from the absorption spectra and the amount of precipitated interstitial oxygen. The experimental absorption spectra can be divided in a set with a Frohlich frequency of around 1100 cm−1 and in a set with a Frohlich frequency between 1110 and 1120 cm−1. It is shown that the shift in the Frohlich frequency is not due to a differing stoichiometry, but to the detailed structure of the reduced spectral function. Inverse modeling of the spectra suggests that the oxide precipitates consist of substoichiometric SiOγ with γ=1.17±0.14.

Experimental and theoretical evidence for vacancy-clustering-induced large voids in Czochralski-grown germanium crystals

Optical inspection of polished Czochralski-grown Ge wafers typically reveals the presence of surface pits similar to the Crystal Originated Particles (COP’s) observed in silicon but in a wider variety of sizes and shapes. Computer simulation of vacancyclustering during the Cz germaniumcrystal growth suggests that the surface pits originate from large voids formed by the diffusion-limited clustering of an excess of vacancies.

Deep level transient spectroscopy study of nickel-germanide Schottky barriers on n-type germanium

Nickel-germanide Schottky barriers have been made on n-type germanium and evaluated by deep level transient spectroscopy in order to detect possible metal indiffusion during the 30s rapid thermal annealing (RTA) employed for the germanidation. It is shown that while no electron traps have been found for the 300 and 350°C RTA step, the double acceptor level at EC−0.3eV of substitutional nickel was observed for the 400 and 450°C samples. The corresponding concentration profile increases exponentially towards the surface from which an effective diffusion coefficient of ∼5×10−10cm2∕s at 450°C has been derived.

Hydrogen plasma-enhanced thermal donor formation in n-type oxygen-doped high-resistivity float-zone silicon

The impact of plasma hydrogenation on the subsequent formation of thermal donors at 450 °C in n-type oxygen-doped high-resistivity float-zone silicon is investigated by a combination of electrical and spectroscopic techniques. It is shown that the increase of the doping concentration can be explained by the creation of two sets of donors. The first one is the classical double oxygen thermal donors (OTDs), which are introduced with a nearly uniform concentration profile across the sample thickness, while the second type of donors is shallower and most likely hydrogen related. The latter show a pronounced concentration profile towards the surface and they form and disappear at a much faster rate than the OTDs at 450 °C.

Observation of surface phonons on the (001) and (100) surfaces of anatase minerals

Abstract The surface properties of TiO2-anatase are of great importance in chemical technology because this material is frequently used as a support for oxide catalysts. In the present work, surface phonons were observed on the (001) and (100) surfaces of anatase minerals by means of HREELS. After comparison with theoretical values and infrared data a preliminary assignment of the observed modes was achieved.