Defects In Semiconductor Materials Research Articles

M-Center in Low-Dose Proton Implanted 4H-SiC; Bistability and Change in Emission Rate

Electrically active point defects in semiconductor materials are important because they strongly affect material properties like effective doping concentration and charge carrier lifetimes. This thesis presents results on point defects introduced by ion implantation in silicon and silicon carbide. The defects have mainly been studied by deep level transient spectroscopy (DLTS) which is a quantitative, electrical characterization method highly suitable for point defect studies. The method is based on measurements of capacitance transients and both standard DLTS and new applications of the technique have been used. In silicon, a fundamental understanding of diffusion phenomena, like room-temperature migration of point defects and transient enhanced diffusion (TED), is still incomplete. This thesis presents new results which brings this understanding a step closer. In the implantation-based experimental method used to measure point defect migration at room temperature, it has been difficult to separate the effects of defect migration and ion channeling. For various reasons, the effect of channeling has so far been disregarded in this type of experiments. Here, a very simple method to assess the amount of channeling is presented, and it is shown that channeling dominates in our experiments. It is therefore recommended that this simple test for channeling is included in all such experiments. This thesis also contains a detailed experimental study on the defect distributions of vacancy and interstitial related damage in ion implanted silicon. Experiments show that interstitial related damage is positioned deeper (0.4 um or more) than vacancy related damage. A physical model to explain this is presented. This study is important to the future modeling of transient enhanced diffusion. Furthermore, the point defect evolution in low-fluence implanted 4H-SiC is investigated, and a large number of new defect levels has been observed. Many of these levels change or anneal out at temperatures below 300 C, which is not in accordance with the general belief that point defect diffusion in SiC requires high temperatures. This thesis also includes an extensive study on a metastable defect which we have observed for the first time and labeled the M-center. The defect is characterized with respect to DLTS signatures, reconfiguration barriers, kinetics and temperature interval for annealing, carrier capture cross sections, and charge state identification. A detailed configuration diagram for the M-center is presented.

Influence of Ion Energy on the Reactive Ion Etching Induced Optical Damage of Gallium Nitride

AbstractReactive Ion Etching (RIE) induces defects in semiconductor materials. These defects can serve as local non-radiative recombination centres for electron-hole pairs, affecting the radiative lifetimes and luminescence efficiencies of the semiconductors. Argon (Ar) and sulphur hexafluoride (SF6) gases were used as etching gases to investigate the influence of ion energy on the RIE induced optical damage of Gallium Nitride (GaN). The significant result of etching by Ar and SF6 gases was that these etching induce defects, but as the total PL does not greatly change, it appears that this process is not increasing the density of nonradiative centres.

Infrared photothermal radiometry of deep subsurface defects in semiconductor materials

Photothermal radiometry (PTR) signals obtained with a highly focused laser beam, were used to obtain amplitude and phase PTR two-dimensional and three-dimensional images of a high-resistivity Si wafer with a mechanical damage on the backsurface, probed from the front (intact) surface. The frequency chosen was 5 kHz, corresponding to an optimal phase resolution of the defect. It is shown that the position of the underlying damage is well resolved in both images, with the phase image showing the expected higher sensitivity in terms of a greater extent of the damage region compared to the amplitude image. The results indicate that the change in carrier lifetime is the major contrast mechanism which can thus be calibrated and labeled as a free-carrier recombination lifetime image (under the same surface recombination conditions).

Radiation-resistant solar cells for space use

This paper reviews the present status of radiation-resistant solar cells made with Si, GaAs, InP and InGaP/GaAs for space use. At first, properties of radiation-induced defects in semiconductor materials and solar cells are described based on an anomalous degradation of Si space solar cells under high-energy, high-fluence electron and proton irradiations. Advantages of direct bandgap materials as radiation-resistant space cells are presented. Unique properties of InP as radiation-resistant cells have also been found. A world-record efficiency of 26.9% (AM0) has been obtained for an InGaP/GaAs tandem solar cell. Radiation-resistance of the InGaP/GaAs tandem cells is described.

Atomic resolution Z-contrast imaging of semiconductors

The direct interpretability of atomic resolution Z-contrast images obtained from a scanning transmission electron microscope (STEM) makes this imaging technique particularly powerful for the analysis of interfaces and defects in semiconductor materials and devices. In this paper, the principles of the technique are outlined and representative examples of its use are presented. In particular, we show the use of Z-contrast imaging to determine the polarity of a CdTe film grown on a Si substrate, the atomic structures of stacking faults and threading dislocation cores in GaN, and the atomistic structure of an ohmic metal/semiconductor contact of Au/GaAs.

Beam optics studies for the planned hybrid electrostatic-magnetic guided slow positron beam in Hong Kong

Design simulations are presented of a variable energy (0–40 keV) slow-positron beam that incorporates the convenience of magnetic guidance with the desirability of some electrostatic focusing produced by a lens structure operating in a low but increasing magnetic field region. Filtering of unmoderated positrons and gamma rays is to be accomplished using two conventionalE×B filters. In a novel way it is proposed that the final beam energy be adjusted using a simple linear de-acceleration stage and that the optimal electrostatic element potentials for efficient extraction, focusing and filtering of positrons be floated relative to the de-acceleration potential. The resulting intense and easily controllable sub-millimetre diameter beam should be suitable for both lateral and depth profiling of defects in semiconductor materials.

Positron and electron solid interactions

Variable-energy positron beams have been attracting considerable attention in recent years as novel probes of surface, thin-film, and interfacial properties in solid systems. The Positron Beam Laboratory at the University of Western Ontario supports research into three separate programs. The first involves the study of re-emitted positrons from thin-films grown on single-crystal substrates under ultra-high vacuum conditions. The second area of research is the non-destructive depth profiling of defects in semiconductor materials. This area promises to dominate positron solid-state research in the near future, as it is rapidly evolving into a very sensitive quantitative probe of structural point defects. The third area of research is the fundamental study of positron and electron scattering and energy loss processes in various solids. This program is especially important in gaining a full theoretical understanding of the positron-solid interaction, which is essential for the application of positron-beam techniques to any area of research. In this manuscript, we briefly introduce and review all of these areas, with a special emphasis on the fundamental collision results.

Positron Annihilation: Industrial Applications Develop

Positrons are often associated with high-energy physics and accelerators, and hence are thought to occupy the realm of basic science. Less well known is the important role they play in materials science after it was discovered in the second half of the 1960s that the results of positron annihilation experiments in solids are strongly dependent on the history of the sample. Following some 25 years of research and development in the laboratory, positron annihilation is now finding its way into industry. This was illustrated by the first Europhysics Industrial Workshop (EIW) on Industrial Applications of Positron Annihilation (10-12 March 1994), where contributions could roughly be divided into three categories: defects in metals, defects in semiconductor materials and devices, and industrial applications of positron tomography.

Phase-stepping microscopy (PSM): a qualification tool for electronic and optoelectronic devices

Phase-stepping microscopy (PSM) is a useful optical metrology technique for the qualification of electronic and optoelectronic devices. Based on interference microscopy, the method uses a CCD camera and a digital image-processing system for automatic fringe analysis, leading to the calculation of the three-dimensional relief of a surface. A vertical resolution of 1 nm is achieved, with a horizontal resolution of 0.6 mu m. The authors describe the PSM system, the performance of the instrument and some of its limitations. To illustrate the uses of PSM, some applications are given in the analysis of defects in semiconductor materials. Results are given of a microprecipitate-related hillock defect on a quaternary layer of InGaAsP on InP made by MOCVD used in the fabrication of lasers. Surface analysis results of an optical guide etched on a quaternary layer are also described. Finally, some initial work is presented in the study of the cross-sectional geometry of the gate recess in FET devices.

Correlation of thermal-wave imaging to other analysis methods

Thermal-wave microscopy is a recent innovation which is potentially very useful for characterizing defects in semiconductor materials. To help understand the mechanisms which generate contrast in thermal-wave micrographs we have done a correlation study with optical microscopy, backscattered electron imaging, electron beam induced current imaging, light beam induced current imaging, and x-ray topography. For this study we used a section of a polycrystalline silicon solar cell. The results show a strong correlation for both crystalline defects and for electrically active defects in this material but thermal-wave microscopy has the advantages of speed of analysis and lack of specimen preparation required.

New STEM spectroscopic techniques for simultaneous electronic analysis and observation of defects in semiconductor materials and devices

The main interest in the study of defects in semiconductor materials lies in their electronic properties and their effects on the device characteristics. Conventional transmission electron microscopy (CTEM) and scanning transmission electron microscopy (STEM) provide the tools for analyzing the crystallographic nature of defects in these materials. However, until now, there have been no techniques which allow for the simultaneous observation of a defect along with an analysis of its electronic properties, e.g., energy level, radiative and nonradiative behavior. We have developed on a STEM unit several techniques which permit displaying and analyzing the spatial distribution of nonradiative and/or radiative recombination centers in a thin semiconductor sample which may be simultaneously analyzed by STEM and CTEM.The first technique uses the electron beam induced current (EBIC) in the thin sample which contains a p-n junction or a Schottky barrier. The surface recombination effects have been minimized to allow for high contrast EBIC images of the recombination centers in the material.

A new spectroscopic technique for imaging the spatial distribution of nonradiative defects in a scanning transmission electron microscope

A new spectroscopic technique for imaging the spatial distribution of nonradiative defects in semiconductor materials is presented. The technique combines the versatility and sensitivity of deep-level transient spectroscopy (DLTS) with the capability for defect analysis at high resolution of the scanning transmission electron microscope. This scanning DLTS method (SDLTS) is illustrated by observing Cu-related defect centers in Ga1−xAlxAs epitaxial layers. A high sensitivity (3×1015 Cu defects cm−3 have been detected) and a spatial resolution of 2 μ or better illustrate the potential of the technique for the study of the electrical behavior of defects in semiconductor devices.