Gerhard Pensl

Bio: Gerhard Pensl is an academic researcher from University of Erlangen-Nuremberg. The author has contributed to research in topics: Deep-level transient spectroscopy & Silicon carbide. The author has an hindex of 44, co-authored 270 publications receiving 7947 citations.

Intrinsic SiC/SiO2 Interface States

Abstract: The energy distribution of electron states at SiC/SiO 2 interfaces produced by oxidation of various (3C, 4H, 6H) SiC polytypes is studied by electrical analysis techniques and internal photoemission spectroscopy. A similar distribution of interface traps over the SiC bandgap is observed for different polytypes indicating a common nature of interfacial defects. Carbon clusters at the SiC/SiO 2 interface and near-interfacial defects in the SiO 2 are proposed to be responsible for the dominant portion of interface traps, while contributions caused by dopant-related defects and dangling bonds at the SiC surface are not observed.

Silicon carbide : recent major advances

Abstract: Zero- and Two-Dimensional Native Defects.- Defect Migration and Annealing Mechanisms.- Hydrogen in SiC.- Electronic Properties of Stacking Faults and Thin Cubic Inclusions in SiC Polytypes.- Principles and Limitations of Numerical Simulation of SiC Boule Growth by Sublimation.- Defect Formation and Reduction during Bulk SiC Growth.- High Nitrogen Doping During Bulk Growth of SiC.- Homoepitaxial and Heteroepitaxial Growth on Step-Free SiC Mesas.- Low-Defect 3D-SiC Grown on Undulant-Si (001) Substrates.- New Development in Hot Wall Vapor Phase Epitaxial Growth of Silicon Carbide.- Formation of SiC Thin Films by Ion Beam Synthesis.- Atomic Structure of SiC Surfaces.- The Continuum of Interface-Induced Gap States.- Contributions to the Density of Interface States in SiC MOS Structures.- Properties of Nitrided Oxides on SiC.- Hall Effect Studies of Electron Mobility and Trapping at the SiC/SiO2 Interface.- Optical Properties of SiC.- Cyclotron Resonance Studies of Effective Masses and Band Structure in SiC.- Electronic Structure of Deep Defects in SiC.- Phosphorus-Related Centers in SiC.- Hall Scattering Factor for Electrons and Holes in SiC.- Radiotracer Deep Level Transient Spectroscopy.- Vacancy Defects Detected by Positron Annihilation.- Characterization of Defects in SiC Crystals by Raman Scattering.- Characterization of Low-Dimensional Structures in SiC Using Advanced Transmission Electron Microscopy.- Synchrotron White Beam X-ray Topography and High Resolution X-ray Diffraction Studies.- Ohmic Contacts for Power Devices on SiC.- Micromachining of SiC.- Surface Preparation Techniques for SiC Wafers.- Epitaxial Growth and Device Processing of SiC on Non-Basal Planes.- SiC Power Bipolar Transistors and Thyristors.- High-Voltage SiC Devices.- Power MOSFETs in 4H-SiC.- Normally-Off Accumulation-Mode Epi-Channel Field Effect Transistor.- Development of SiC Devices for Microwave and RF Power Amplifiers.- Advances in SiC Field Effect Gas Sensors

Deep Defect Centers in Silicon Carbide Monitored with Deep Level Transient Spectroscopy

Abstract: Electrical data obtained from deep level transient spectroscopy investigations on deep defect centers in the 3C, 4H, and 6H SiC polytypes are reviewed Emphasis is put on intrinsic defect centers observed in as-grown material and subsequent to ion implantation or electron irradiation as well as on defect centers caused by doping with or implantation of transition metals (vanadium, titanium, chromium, and scandium)

Doping of SiC by Implantation of Boron and Aluminum

Abstract: Experimental studies on aluminum (Al) and boron (B) implantation in 4H/6H SiC are reported; the implantation is conducted at room temperature or elevated temperatures (500 to 700 C). Both Al and B act as ``shallow`` acceptors in SiC. The ionization energy of these acceptors, the hole mobility and the compensation in the implanted layers are obtained from Hall effect investigations. The degree of electrical activity of implanted Al/B atoms is determined as a function of the annealing temperature. Energetically deep centers introduced by the Al{sup +}/B{sup +} implantation are investigated. The redistribution of implanted Al/B atoms subsequent to anneals and extended lattice defects are monitored. The generation of the B-related D-center is studied by coimplantation of Si/B and C/B, respectively. (orig.) 60 refs.

Fundamentals of zinc oxide as a semiconductor

Abstract: In the past ten years we have witnessed a revival of, and subsequent rapid expansion in, the research on zinc oxide (ZnO) as a semiconductor. Being initially considered as a substrate for GaN and related alloys, the availability of high-quality large bulk single crystals, the strong luminescence demonstrated in optically pumped lasers and the prospects of gaining control over its electrical conductivity have led a large number of groups to turn their research for electronic and photonic devices to ZnO in its own right. The high electron mobility, high thermal conductivity, wide and direct band gap and large exciton binding energy make ZnO suitable for a wide range of devices, including transparent thin-film transistors, photodetectors, light-emitting diodes and laser diodes that operate in the blue and ultraviolet region of the spectrum. In spite of the recent rapid developments, controlling the electrical conductivity of ZnO has remained a major challenge. While a number of research groups have reported achieving p-type ZnO, there are still problems concerning the reproducibility of the results and the stability of the p-type conductivity. Even the cause of the commonly observed unintentional n-type conductivity in as-grown ZnO is still under debate. One approach to address these issues consists of growing high-quality single crystalline bulk and thin films in which the concentrations of impurities and intrinsic defects are controlled. In this review we discuss the status of ZnO as a semiconductor. We first discuss the growth of bulk and epitaxial films, growth conditions and their influence on the incorporation of native defects and impurities. We then present the theory of doping and native defects in ZnO based on density-functional calculations, discussing the stability and electronic structure of native point defects and impurities and their influence on the electrical conductivity and optical properties of ZnO. We pay special attention to the possible causes of the unintentional n-type conductivity, emphasize the role of impurities, critically review the current status of p-type doping and address possible routes to controlling the electrical conductivity in ZnO. Finally, we discuss band-gap engineering using MgZnO and CdZnO alloys.

Large‐band‐gap SiC, III‐V nitride, and II‐VI ZnSe‐based semiconductor device technologies

Abstract: In the past several years, research in each of the wide‐band‐gap semiconductors, SiC, GaN, and ZnSe, has led to major advances which now make them viable for device applications. The merits of each contender for high‐temperature electronics and short‐wavelength optical applications are compared. The outstanding thermal and chemical stability of SiC and GaN should enable them to operate at high temperatures and in hostile environments, and also make them attractive for high‐power operation. The present advanced stage of development of SiC substrates and metal‐oxide‐semiconductor technology makes SiC the leading contender for high‐temperature and high‐power applications if ohmic contacts and interface‐state densities can be further improved. GaN, despite fundamentally superior electronic properties and better ohmic contact resistances, must overcome the lack of an ideal substrate material and a relatively advanced SiC infrastructure in order to compete in electronics applications. Prototype transistors have been fabricated from both SiC and GaN, and the microwave characteristics and high‐temperature performance of SiC transistors have been studied. For optical emitters and detectors, ZnSe, SiC, and GaN all have demonstrated operation in the green, blue, or ultraviolet (UV) spectra. Blue SiC light‐emitting diodes (LEDs) have been on the market for several years, joined recently by UV and blue GaN‐based LEDs. These products should find wide use in full color display and other technologies. Promising prototype UV photodetectors have been fabricated from both SiC and GaN. In laser development, ZnSe leads the way with more sophisticated designs having further improved performance being rapidly demonstrated. If the low damage threshold of ZnSe continues to limit practical laser applications, GaN appears poised to become the semiconductor of choice for short‐wavelength lasers in optical memory and other applications. For further development of these materials to be realized, doping densities (especially p type) and ohmic contact technologies have to be improved. Economies of scale need to be realized through the development of larger SiC substrates. Improved substrate materials, ideally GaN itself, need to be aggressively pursued to further develop the GaN‐based material system and enable the fabrication of lasers. ZnSe material quality is already outstanding and now researchers must focus their attention on addressing the short lifetimes of ZnSe‐based lasers to determine whether the material is sufficiently durable for practical laser applications. The problems related to these three wide‐band‐gap semiconductor systems have moved away from materials science toward the device arena, where their technological development can rapidly be brought to maturity.

Luminescence properties of defects in GaN

Abstract: Gallium nitride (GaN) and its allied binaries InN and AIN as well as their ternary compounds have gained an unprecedented attention due to their wide-ranging applications encompassing green, blue, violet, and ultraviolet (UV) emitters and detectors (in photon ranges inaccessible by other semiconductors) and high-power amplifiers. However, even the best of the three binaries, GaN, contains many structural and point defects caused to a large extent by lattice and stacking mismatch with substrates. These defects notably affect the electrical and optical properties of the host material and can seriously degrade the performance and reliability of devices made based on these nitride semiconductors. Even though GaN broke the long-standing paradigm that high density of dislocations precludes acceptable device performance, point defects have taken the center stage as they exacerbate efforts to increase the efficiency of emitters, increase laser operation lifetime, and lead to anomalies in electronic devices. The p...

Semiconductor device, and manufacturing method thereof

Abstract: An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor ultraviolet detectors

Abstract: In this review article a comprehensive analysis of the developments in ultraviolet (UV) detector technology is described. At the beginning, the classification of UV detectors and general requirements imposed on these detectors are presented. Further considerations are restricted to modern semiconductor UV detectors, so the basic theory of photoconductive and photovoltaic detectors is presented in a uniform way convenient for various detector materials. Next, the current state of the art of different types of semiconductor UV detectors is presented. Hitherto, the semiconductor UV detectors have been mainly fabricated using Si. Industries such as the aerospace, automotive, petroleum, and others have continuously provided the impetus pushing the development of fringe technologies which are tolerant of increasingly high temperatures and hostile environments. As a result, the main efforts are currently directed to a new generation of UV detectors fabricated from wide band‐gap semiconductors the most promising ...