Schottky diode | EPFL Graph Search

The Schottky diode (named after the German physicist Walter H. Schottky), also known as Schottky barrier diode or hot-carrier diode, is a semiconductor diode formed by the junction of a semiconductor with a metal. It has a low forward voltage drop and a very fast switching action. The cat's-whisker detectors used in the early days of wireless and metal rectifiers used in early power applications can be considered primitive Schottky diodes. When sufficient forward voltage is applied, a current flows in the forward direction. A silicon p–n diode has a typical forward voltage of 600–700 mV, while the Schottky's forward voltage is 150–450 mV. This lower forward voltage requirement allows higher switching speeds and better system efficiency. Construction A metal–semiconductor junction is formed between a metal and a semiconductor, creating a Schottky barrier (instead of a semiconductor–semiconductor junction as in conventional diodes). Typical metals used are molybdenum,

Synthesis and characterization of group II-Vi semiconductor nanowires

Holger Jens Böttcher

Semiconductor nanowires are an emerging class of nanostructures that represent attractive building blocks for nanoscale electronic and photonic devices. To the present, nanowires are synthesized on a small scale by experimentally demanding gas phase deposition techniques. This thesis describes a simple and cost-efficient solution-based synthesis towards high-quality nanowires of Group II-VI compound semiconductors. The effects of various reaction parameters and of doping on the wires' structural, electrical and magnetic properties are investigated. The first part of this thesis is dedicated to a novel variant of the solvothermal synthesis of CdS nanowires employing a single-source precursor. The wires are of single-crystalline quality and can be indexed to wurtzite-type bulk CdS with the preferential growth direction along the axis. As-grown nanowires have a smooth surface, are up to 40 µm long and exhibit aspect ratios up to 1000. The wires' aspect ratio can be increased by choosing a low precursor concentration. Time-dependent experiments reveal the wires to axially grow at a rate of ≈1µm/h while lateral growth only occurs during the initial reaction phase. As shown by photoluminescence spectroscopy the surface defect density can be significantly lowered by raising the reaction temperature from 180 to 200 °C. Electrically contacted CdS nanowires are highly resistive in the dark, but become more conductive by 4 orders of magnitude upon illumination above the bandgap energy (λ

EPFL2010

Ab initio study of interface states at metal contacts to III-IV semiconductors

Thomas Maxisch

We present a theoretical study of the physical characteristics of metal/semiconductor junctions. Using first principle pseudopotential calculations, we have investigated the nature of electronic states with energies within the semiconductor band gap of representative abrupt, defect-free, anion-terminated metal/III-V interfaces. Namely, we focused on Al contacts to GaAs(001), AlAs(001) and cubic GaN(001) as well as on Al, Au and Cu junctions to cubic GaN(001). Recent advances in Schottky barrier concepts emphasize the possible relationship between interface states and the formation of the Schottky barrier. We aim at understanding the atomic-scale mechanisms responsible for interface states as well as their role in the Schottky barrier formation process. At As-terminated Al/GaAs(001) and Al/AlAs(001) junctions, resonant and localized interface states occur at the J point of the interface 2D Brillouin zone near the Fermi energy in the semiconductor midgap region. They correspond to intermetallic bonds between the outermost cation atoms of the semiconductor and the interfacial Al atoms of the metal. These interface states derive from an interaction between localized states of the Al(001) surface and semiconductor conduction band states, mediated by localized states of the unreconstructed, As-terminated semiconductor (001) surface. Our results indicate that interface states of the intermetallic, bonding-like kind could play an important role in the transport properties of metal/AlxGa1-xAs junctions. We have also investigated the electronic structure of Al, Au and Cu junctions to cubic, N-terminated GaN(001). The localized interface state reported for As-terminated Al/GaAs(001) and Al/AlAs(001) junctions occurs also at metal/GaN interfaces under the condition that atoms on the outermost atomic plane of the metal are placed in front of the outermost semiconductor cation. This indicates that the formation mechanism of this state is a very general one. In contrast to Al/AlxGa1-xAs junctions, these states occur at energy much larger than EF for the contacts to GaN. Thus, they are not expected to contribute significantly to the electronic transport of the latter interfaces. However, a large number of interface states attributed to d-type orbitals occur over a wide energy range including EF at contacts of noble metals to GaN.

EPFL2003

Electron Emission Regimes of Planar Nano Vacuum Emitters

Alberto Nardi, Marco Turchetti, Yujia Yang

Recent advancements in nanofabrication have enabled the creation of vacuum electronic devices with nanoscale free-space gaps. These nanoelectronic devices promise the benefits of cold-field emission and transport through free space, such as high nonlinearity and relative insensitivity to temperature and ionizing radiation, all while drastically reducing the footprint, increasing the operating bandwidth, and reducing the power consumption of each device. Furthermore, planarized vacuum nanoelectronics could easily be integrated at scale similar to typical microscale and nanoscale semiconductor electronics. However, the interplay between different electron emission mechanisms from these devices is not well understood, and inconsistencies with pure Fowler-Nordheim (FN) emission have been noted by others. In this work, we systematically study the current-voltage characteristics of planar vacuum nanodevices having few-nanometer radii of curvature and free-space gaps between the emitter and the collector. By investigating the current-voltage characteristics of nearly identical devices fabricated from two different materials and under various environmental conditions, such as temperature and atmospheric pressure, we are able to clearly isolate three distinct emission regimes within a single device: Schottky, FN, and saturation. Our work will enable robust and accurate modeling of vacuum nanoelectronics, which will be critical for future applications requiring high-speed and low-power electronics capable of operation in extreme conditions.

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC2022

Ab initio study of interface states at metal contacts to III-IV semiconductors

Thomas Maxisch

EPFL2003