63 research outputs found
Study of X-ray Radiation Damage in Silicon Sensors
The European X-ray Free Electron Laser (XFEL) will deliver 30,000 fully
coherent, high brilliance X-ray pulses per second each with a duration below
100 fs. This will allow the recording of diffraction patterns of single complex
molecules and the study of ultra-fast processes. Silicon pixel sensors will be
used to record the diffraction images. In 3 years of operation the sensors will
be exposed to doses of up to 1 GGy of 12 keV X-rays. At this X-ray energy no
bulk damage in silicon is expected. However fixed oxide charges in the
insulating layer covering the silicon and interface traps at the Si-SiO2
interface will be introduced by the irradiation and build up over time.
We have investigated the microscopic defects in test structures and the
macroscopic electrical properties of segmented detectors as a function of the
X-ray dose. From the test structures we determine the oxide charge density and
the densities of interface traps as a function of dose. We find that both
saturate (and even decrease) for doses between 10 and 100 MGy. For segmented
sensors the defects introduced by the X-rays increase the full depletion
voltage, the surface leakage current and the inter-pixel capacitance. We
observe that an electron accumulation layer forms at the Si-SiO2 interface. Its
width increases with dose and decreases with applied bias voltage. Using TCAD
simulations with the dose dependent parameters obtained from the test
structures, we are able to reproduce the observed results. This allows us to
optimize the sensor design for the XFEL requirements
Scaling analysis of electron transport through metal-semiconducting carbon nanotube interfaces: Evolution from the molecular limit to the bulk limit
We present a scaling analysis of electronic and transport properties of
metal-semiconducting carbon nanotube interfaces as a function of the nanotube
length within the coherent transport regime, which takes fully into account
atomic-scale electronic structure and three-dimensional electrostatics of the
metal-nanotube interface using a real-space Green's function based
self-consistent tight-binding theory. As the first example, we examine devices
formed by attaching finite-size single-wall carbon nanotubes (SWNT) to both
high- and low- work function metallic electrodes through the dangling bonds at
the end. We analyze the nature of Schottky barrier formation at the
metal-nanotube interface by examining the electrostatics, the band lineup and
the conductance of the metal-SWNT molecule-metal junction as a function of the
SWNT molecule length and metal-SWNT coupling strength. We show that the
confined cylindrical geometry and the atomistic nature of electronic processes
across the metal-SWNT interface leads to a different physical picture of band
alignment from that of the planar metal-semiconductor interface. We analyze the
temperature and length dependence of the conductance of the SWNT junctions,
which shows a transition from tunneling- to thermal activation-dominated
transport with increasing nanotube length. The temperature dependence of the
conductance is much weaker than that of the planar metal-semiconductor
interface due to the finite number of conduction channels within the SWNT
junctions. We find that the current-voltage characteristics of the metal-SWNT
molecule-metal junctions are sensitive to models of the potential response to
the applied source/drain bias voltages.Comment: Minor revision to appear in Phys. Rev. B. Color figures available in
the online PRB version or upon request to: [email protected]
Effect of post-oxidation annealing on the electrical properties of anodic oxidized films in pure water
The work presented here consists of investigating and studying the electronic properties of anodic oxide film (SiO2). This study deals to the determination of interface states density Si/SiO2 and the study of electronic conduction. MOS capacitors with anodic oxides (9nm) were elaborated. The anodic silica films were produced by anodization of monocristalline silicon wafers in pure water in an electrolysis cell (P.T.F.E) at room temperature, with a constant current density of 20 μA/cm2. Film thickness increases linearly as a function of total charge during oxidation Using C(V),G(ω),I(V) measurements, we have determined the interface states density, fixed charges density and conduction mechanism which is of Fowler – Nordheim type for annealed oxides at various temperature
- …