Avalanche photodiode

Summary

An avalanche photodiode (APD) is a highly sensitive semiconductor photodiode detector that exploits the photoelectric effect to convert light into electricity. From a functional standpoint, they can be regarded as the semiconductor analog of photomultiplier tubes. The avalanche photodiode (APD) was invented by Japanese engineer Jun-ichi Nishizawa in 1952. However, study of avalanche breakdown, microplasma defects in silicon and germanium and the investigation of optical detection using p-n junctions predate this patent. Typical applications for APDs are laser rangefinders, long-range fiber-optic telecommunication, and quantum sensing for control algorithms. New applications include positron emission tomography and particle physics. Principle of operation By applying a high reverse bias voltage (typically 100–200 V in silicon), APDs show an internal current gain effect (around 100) due to impact ionization (avalanche effect). However, some silicon APDs employ alternative dop

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https://en.wikipedia.org/wiki/Avalanche_photodiode

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The first part of this thesis describes the development of an optimised LSO/LuYAP phoswich detector head for the ClearPET demonstrator positron emission tomograph (PET) dedicated to small animals that is under construction in Lausanne within the Crystal Clear Collaboration. The detector head consists of a dual layer of 8 x 8 LSO and LuYAP crystal arrays coupled to a multi-anode photomultiplier tube (MaPMT). Equalistion of the LSO/LuYAP light collection is obtained through partial attenuation of the LSO scintillation light using a thin aluminium deposit of 20-35 nm on LSO and appropriate temperature regulation of the phoswich head between 30 to 60°C. At 511 keV, typical FWHM energy resolutions of the pixels of a phoswich head amounts to (28±2)% for LSO and (25±2)% for LuYAP. The LSO versus LuYAP crystal identification efficiency is better than 98%. Eighteen detector modules have been mounted on a rotating gantry. Radial and tangential spatial resolutions were measured up to 4 cm from the scanner axis and compared to Monte Carlo simulations using GATE. FWHM spatial resolution ranges from 1.3 mm on axis to 2.6 mm at 4 cm from the axis. Time resolution was measured for several event tagging methods. Pulse shape discrimination methods with an efficiency of 97-99% were developed for LSO/LuAP and LuAP/LuYAP phoswich among these, some are based on neural networks. The second part of this work is devoted to characterisation measurements performed on several recently developed arrays of avalanche photodiodes (APDs) with the perspective of replacing MaPMTs. Their doping profile were estimated from the dependence of capacitance on junction voltage. Quantum efficiency was measured as a function of wavelength in the range of 300-700 nm. Bulk and surface contributions to the dark current were estimated. Gain and excess noise factor were measured as a function of bias voltage. The S8550 APD array produced by Hamamatsu Photonics appears as being the best candidate for an aplication in PET. The last part of this thesis is dedicated to a prospective study performed on S8550 APD arrays coupled to LSO and LuAP crystals. Energy resolution and its contributions as well as time resolution were measured on modules having a single layer of LSO and LuAP crystals. Two staggered LSO/LSO and LSO/LuAP assemblies were evaluated regarding depth of interaction identification efficiency and energy resolution. Finally, a synthesis of the results obtained is presented.

EPFL2006

Characterisation of arrays of avalanche photodiodes for small animal positron emission tomography

Jean-François Loude, Jean-Baptiste Mosset

2003

High Performance InP-Based Quantum Dash Semiconductor Mode-Locked Lasers for Optical Communications

Anthony Martinez

Several applications are pushing the development of high performance mode-locked lasers: generation of short pulses for extremely high bit rate transmission at 100 Gb/s and beyond, all-optical clock recovery at 40 Gb/s and beyond, generation of millimeter wave signals through mode-beating on a high speed photodiode, optical sampling for analog-to-digital conversion, and generation of wavelength-division-multiplexing channels. This paper will report on new advances in InP-based quantum dash mode-locked lasers, which largely surpass the performance of their bulk or quantum well counterparts in terms of the mode-beating spectral purity and the bandwidth of optical spectrum. In particular, we will describe the quantum dash nanostructures used for the mode-locked lasers and the dependence of the mode-locking properties on detailed quantum dash structures. We will demonstrate that these quantum dash lasers can be actively mode-locked, generating sub-picosecond or picosecond pulses at different repetition frequencies with extremely low timing jitter. They can also be used to achieve all-optical clock recovery, with timing jitter compliant with International Telecommunication Union (ITU) standards even for highly degraded input optical signal-to-noise ratio. Finally, we demonstrate that, owing to the very wide and flat optical spectrum and the low relative-intensity noise level of the mode-locked laser, error-free transmission over 50 km single mode fiber has been achieved for eight wavelength division multiplexing ITU channels at 10 Gb/s with a channel spacing of 100 GHz. (C) 2009 Alcatel-Lucent.

2009

EPFL2006