Using a modified photoconductive eddy-current technique, excess carrier decay can be measured and used to identify the specific defect dominating recombination. As the dynamic range of the measurement system is linear over about three orders of magnitude, the injection-level spectroscopy technique can be performed in a single measurement for rapid defect identification.

A study of point defects in II-VI compound semiconductors was undertaken and has revealed that open volume defects are present in a wide variety of these samples. Zn-based binary compounds contain primarily neutral divacancy defects in concentrations in the mid 1016 cm−3. CdTe samples contain neutral monovacancy sized defect complexes in the high 1016 cm−3 range. When a small fraction of Zn or Se is alloyed into CdTe the defect profile changes dramatically to one dominated by divacancy sized defects at roughly half the original concentration.

We present x-ray fluorescence (XRF) results from studies of metal impurities in silicon. A synchrotron-based XRF microprobe, with μm spatial resolution, was used to detect and map the impurities. The sensitivity of the XRF microprobe was determined for copper and iron in silicon using well-characterized standard samples. We have concluded the system can detect one iron or copper precipitate in silicon with a radius of ≈14nm. This sensitivity pertains to other relevant impurities in silicon, such as, chromium, manganese, cobalt, nickel and gold. Furthermore, we have detected and spatially mapped metal impurity precipitates in silicon, which are undetectable by Energy Dispersive Spectroscopy in a Scanning Electron Microscope. These results exhibit the extraordinary sensitivity of the XRF microprobe for metal impurities in semiconductors.

The ionization of deep impurity centers by high intensity far-infrared radiation, with photon energies tens of times lower than the impurity binding energy, has been investigated. It is shown that the ionization is caused by phonon-assisted tunneling in the electric field of radiation, in which carrier emission is accompanied by electron tunneling and defect tunneling in the configuration space. The field and temperature dependencies of the ionization probability allow to obtain defect parameters like tunneling times and the Huang-Rhys factor as well as the basic structure of the defect adiabatic potentials. In very strong fields, the ionization changes to direct tunneling without assistance of phonons. It is shown that for the case of charged impurities and in a relatively low electric field strength the Poole-Frenkel effect plays a dominant role in ionization, which allows to identify the charge state of the center. Within a broad range of intensities, wavelengths and temperature, the terahertz electric field of the radiation acts as a static field. An enhancement of tunneling with increase of frequency has been observed for very high frequencies or low temperatures.

High resistivity CdTe:In and CdZnTe samples were studied by means of continuos and picosecond time-resolved photoluminescence (PL). Detected PL signal is affected by non-radiative trapping into defects, while radiative recombination has an excitonic character. Time-resolved PL can be described by two lifetimes: the first (30-60 ps) takes into account fast non radiative recombination, the second in the range 200-300 ps can be related to exciton decay.

Lifetime spectroscopy is a valuable tool in a number of silicon-based technologies. Currently, lifetime measurement is the most sensitive diagnostic for identification of lowlevel metal impurities in silicon by using the ratio of high-injection to low-injection lifetime. When a single impurity dominates recombination, the lifetime as a function of injection level provides a measure of the defect concentration. Another measurement parameter, that has not been commonly used, is the lifetime as a function of temperature. Temperaturedependent lifetime analysis leads to a better understanding of trapping-delayed recombination rates, trapping and recombination center energy levels and activation energies, temperaturedependent capture cross sections, and surface or grain boundary recombination or trapping effects. A contactless measurement technique has been developed that provides the sample's recombination lifetime over a temperature range from 80 K to 300 K. A sample is coupled to the measurement circuitry that is placed into a Dewar where it is cooled by liquid nitrogen. Lifetimes are then measured as the sample is allowed to warm to room temperature. Data will be shown on these variable-temperature lifetime measurements, which have been made on silicon wafer material ranging from high-quality float-zone-grown wafers to low-cost polycrystalline materials used in photovoltaics.

The structure of planar defects in GaP films grown by MBE on Si (110) was investigated by transmission electron microscopy. Growth of GaP films on the (110) surface produced numerous microtwins which formed both first and second order twin boundaries. Using high-resolution transmission electron microscopy, the atomic structure of Σ=3 and Σ=9 twin boundaries were studied. Both the Σ=3 and Σ=9 interfaces were observed to facet along specific crystallographic planes. Geometric models of the Σ=9 {221} twin boundary accounting for different polar bonding configurations were proposed and compared with experimental observations.

A novel wafer scale detection system for defects and chemical contamination in semiconductors based upon the Scanning Kelvin Probe (SKP) is presented. It incorporates traditional work function (wf) topography with high resolution (<0.1 meV), Surface Photovoltage (SPV) measurement and the acquisition of SPV transients with time constants down to I ts. This permits quasi-simultaneous determination of surface charge, surface barrier height and bulk minority carrier lifetime. Monitoring variations of these parameters after chemical treatments give an accurate indication of the location and amount of contamination.

The SKP system is introduced and the SPV and SPV transient measurement modes are discussed. Measurements on Fe-contaminated and Au-implanted Si wafers demonstrate the feasibility of the system for defect and impurity characterisation in semiconductors. The system is both non-contact and non-destructive, requires no wafer preparation and can be applied in both ambient and vacuum environments.

The Optical Precipitate Profiler (OPP) and similar instruments are establishing themselves as routine techniques for measuring bulk micro-defect density (BMD) and denuded zone depths in semiconductor wafers. This task has traditionally been done by means of the cleave-and-etch technique in which defects are counted on a cleaved edge of an etched wafer using an optical microscope. The OPP makes this task faster, simpler and more accurate. In addition it can perform the measurement on a whole wafer.

We have used the OPP to measure defect density and scattering intensities from a set of silicon wafers with different precipitate sizes. The wafers were all given the same nucleation heat treatment but the precipitates were then grown at 1000°C for 1, 2, 4, 8, 16 and 32 hours. The size distributions and densities of the precipitates in each wafer were determined by Transmission Electron Microscopy (TEM). In a second experiment wafers with precipitate densities varying over four orders of magnitude as determined by cleaveand-etch were also measured by the OPP.

From these experiments we have estimated that the OPP can detect defects with an equivalent radius of 16 ± 8 nm and larger. We have also found that the scattering voltage (strength) depends on the precipitate radius, r3, as approximately r3 and that there is an upper number density limit above which the OPP is unable to measure the precipitate density accurately. For our setup this upper density limit was about 1.5 - 2.0 × 1010 defects/cm3 as measured by cleave-and-etch.

Annealing of multicrystalline silicon wafers in argon at temperatures higher than 800°C increases the recombination strength of extended defects irreversibly, while external gettering techniques applied at the same temperatures reduce their recombination strength. It is observed that in the light beam induced current (LBIC) scan maps at 80 K the contrast of some extended defects in raw samples is enhanced and additional defects are detected. The same features of defects are revealed by the LBIC maps of raw samples at 80 K as well as at 300 K after annealing. In other words, the LBIC scan maps at low temperature detect “sleeping” defects, which do not recombine at 300 K, but which are activated by thermal treatments during processing steps. The results can be explained by the Shockley-Read-Hall statistic involving the presence of deep and shallow energy levels in the band gap associated with the impurity-defect interaction.

Cathodoluminescence (CL) in the scanning electron microscope (SEM) has been used to investigate the effect of doping with an isoelectronic dopant, aluminum, on the native acceptors and on the general structure of extended defects of gallium antimonide single crystals. While there is no significant change in the native defect content, decoration of non-radiative recombination centers or extended defects occurs as a result of aluminum doping.

We have performed a systematic study of the effect of various phosphorus passivation techniques on the room temperature photoluminescence (PL) intensity of undoped GaAs. The effects of passivation by two methods are compared: (1) the P-exchange reaction on exposure to tertiarybutylphosphine (TBP) vapour between 500-620°C, and (2) the growth of thin layers of GaP directly on GaAs. An x-ray diffraction technique was used to estimate the thickness of the passivating layers. Reflectance difference spectroscopy indicated a similar chemical origin for the two passivation methods. Both passivation techniques resulted in strong enhancements in the room temperature PL. PL intensity was observed to increase very rapidly with adsorbed P for both cases saturating at approximately 2 monolayers equivalent GaP coverage.

Selenium disulfide surface treatment can unpin the surface Fermi-level on n-GaAs (100) surfaces, resulting in a reduction in the surface band bending. The long-term stability of the surface Fermi-level unpinning has been studied using photoreflectance spectroscopy under room ambient conditions. Our results show that the SeS2-treated n-GaAs (100) surface is stable up to four months with negligible shift in the surface Fermi-level being noted. The mechanism of the long-term stability is attributed to the layered surface structure formed on the SeS2-treated n- GaAs (100) surface. The chemical structure of the passivated surface was determined by synchrotron radiation photoemission spectroscopy. The outermost layer of sulfur and arsenicbased sulfides and selenides may protect the electronic passivating layer, which consists of gallium-based selenides, from interaction with the atmosphere.

In this work, we present results and analysis which demonstrate the influence of rapid thermal annealing (RTA) on the properties of the Si(100)-SiO2 interface. Polysilicon/oxide/silicon capacitor structures were subjected to RTA treatments, in a nitrogen ambient, over the temperature range 600-1050°C. The structures were examined using high frequency and quasi-static capacitance-voltage (CV) analysis to determine the interface state density profile across the energy gap immediately following the RTA step. The effect of hydrogen annealing subsequent to the RTA process is also presented. Based on the analysis of the interface state density profiles, it is suggested in this work, that RTA (T > 600°C) exposes silicon dangling bond (Pb) centres at the Si(100)-SiO2 interface. The implications of this work to the study of the Si-SiO2 interface, and the technological implications for silicon based MOS processes, are discussed.

A Molecular Dynamics simulation method has been applied to the motion of steps on a surface vicinal to {100}in Si. Undulation of the steps and ‘kissing sites’ are observed to arise from thermal fluctuations at 300°K. The dependence of the characteristic energy of these configurations on the terrace width complies with a free fermion picture which also includes dipolar and nearest neighbours interactions.