Omeime Xerviar Esebamen

Fabrication, characterization and simulation of channel stop for n in p-substrate silicon pixel detectors

Silicon detectors made on p-substrates are expected to have a better radiation hardness as compared to detectors made on n-substrates. However, the fixed positive oxide charges induce an inversion layer of electrons in the substrate, which connects the pixels. The common means of solving this problem is by using a p-spray, individual p-stops or a combination of the two. Here, we investigate the use of field plates to suppress the fixed positive charges and to prevent the formation of an inversion layer. The fabricated detector shows a high breakdown voltage and low interpixel leakage current for a structure using biased field plates with a width of 20 μm. By using a spice model for simulation of the preamplifier, a cross talk of about 1.6% is achieved with this detector structure. The cross talk is caused by capacitive and resistive coupling between the pixels.

N+P photodetector characterization using the quasi-steady state photoconductance decay method

When a material is irradiated, it becomes more electrically conductive due to the absorption of the electromagnetic radiation. As a result, the number of free electrons and holes changes and raises its electrical conductivity. A simple but interesting phenomenon to characterise a fabricated n+p photodetector in order to determine its linearity (photoresponse) and photoconductance was employed. Using the transient decay when the irradiation source is switched off, the minority carrier concentration, effective lifetime and surface recombination velocity present at the surface of the detector were measured.

A different approach for determining the responsivity of n+p detectors using scanning electron microscopy

This paper explores an alternative to the standard method of studying the responsivities (the input—output gain) and other behaviours of detectors at low electron energy. The research does not aim to compare the results of differently doped n+p detectors; its purpose is to provide an alternative characterization method (using scanning electron microscopy) to those used in previous studies on the responsivity of n+p doped detectors as a function of the electron radiation energy and other interface parameters.

Surface state effects on N+P doped electron detector

Surface states and interface recombination velocity that exist between detector interfaces have always been known to affect the performance of a detector. This article describes how the detector performance varies when the doping profile is altered. When irradiated with electrons, the results show that while changes in the doping profile have an effect of the detector responsivity with respect to the interface recombination velocity vs, there is no visible effect with respect to fixed oxide charge Qf otherwise known as interface fixed charge density.

Simulation and measurement of short infrared pulses on silicon position sensitive device

Lateral position sensitive devices (PSD) are important for triangulation, alignment and surface measurements as well as for angle measurements. Large PSDs show a delay on rising and falling edges when irradiated with near infra-red light. This delay is also dependent on the spot position relative to the electrodes. It is however desirable in most applications to have a fast response. We investigated the responsiveness of a Sitek PSD in a mixed mode simulation of a two dimensional full sized detector. For simulation and measurement purposes focused light pulses with a wavelength of 850 nm, duration of 1μs and spot size of 280μm were used. The cause for the slopes of rise and fall time is due to time constants of the device capacitance as well as the photo-generation mechanism itself. To support the simulated results, we conducted measurements of rise and fall times on a physical device. Additionally, we quantified the homogeneity of the device by repositioning a spot of light from a pulsed ir-laser diode on the surface area.

High resolution, low energy electron detector

Electron detection at low energy range for scanning electron microscope (SEM), electron capture detector and electron probe micro-analysis (EPMA) applications, require detectors with high sensitivity and accuracy for low energy range. Such detectors must therefore have a thin entrance window and low recombination at the Si-SiO2 interface. An electron detector with 100% photons to electron-hole pair production rate having a 10 nm SiO2 passivating layer reveals a responsivity of approximately 0.25 A/W when irradiated. Simulations results showing the responsivity of electron interaction between detectors of varied interface fixed oxide charge density Qf show that there is an appreciable difference with the responsivity of a p+n detector and that of an n+p. The simulation results also show the significance of the effect of the minority carriers transport velocity Sn,p on the responsivity of the detector.

Spectral Performance of Photon Counting Pixel Detector Using Attenuation Spectra for Test Samples

When a material is placed along the path of an X‐ray beam using a broad range of energy X‐ray source, the energy dependence of the attenuation for the X‐ray photons will be substantially dissimilar for different materials. The process at which X‐ray radiation loses its penetrating strength as it travels through a material will be significantly larger for photons with energy above k‐edge energy of that material than for those with slightly lower energy. Hence energy resolved X‐ray imaging can be used to achieve colour images revealing the material content of the test sample. The attenuation of the spectrum done by scanning an energy window through the spectrum was measured for a number of samples of different materials. The test samples include Sn, Gd and I with K‐edge energy at 29 keV, 50 keV and 33 keV, respectively, using a Feinfocus microfocus X‐ray source (FTP‐105.02) with Medipix2 photon counting chip.