J.C. Jackson

A novel silicon Geiger-mode avalanche photodiode

Dark count nonlinearity in CMOS compatible, single photon counting, Geiger-mode avalanche photodiodes (GM-APD) has been investigated. A novel structure was designed, fabricated, and characterized to allow dark count optimization. Dark count levels for the proposed structure are shown to scale linearly with area.

Characterization of Geiger Mode Avalanche Photodiodes for Fluorescence Decay Measurements

Geiger mode avalanche photodiodes (APD) can be biased above the breakdown voltage to allow detection of single photons. Because of the increase in quantum efficiency, magnetic field immunity, robustness, longer operating lifetime and reduction in costs, solid-state detectors capable of operating at non-cryogenic temperatures and providing single photon detection capabilities provide attractive alternatives to the photomultiplier tube (PMT). Shallow junction Geiger mode APD detectors provide the ability to manufacture photon detectors and detector arrays with CMOS compatible processing steps and allows the use of novel Silicon-on-Insulator(SoI) technology to provide future integrated sensing solutions. Previous work on Geiger mode APD detectors has focused on increasing the active area of the detector to make it more PMT like, easing the integration of discrete reaction, detection and signal processing into laboratory experimental systems. This discrete model for single photon detection works well for laboratory sized test and measurement equipment, however the move towards microfluidics and systems on a chip requires integrated sensing solutions. As we move towards providing integrated functionality of increasingly nanoscopic sized emissions, small area detectors and detector arrays that can be easily integrated into marketable systems, with sensitive small area single photon counting detectors will be needed. This paper will demonstrate the 2-dimensional and 3-dimensional simulation of optical coupling that occurs in Geiger mode APDs. Fabricated Geiger mode APD detectors optimized for fluorescence decay measurements were characterized and preliminary results show excellent results for their integration into fluorescence decay measurement systems.

Study of the Properties of New SPM Detectors

The operation and performance of multi-pixel, Geiger-mode APD structures referred to as Silicon Photomultiplier (SPM) are reported. The SPM is a solid state device that has emerged over the last decade as a promising alternative to vacuum PMTs. This is due to their comparable performance in addition to their lower bias operation and power consumption, insensitivity to magnetic fields and ambient light, smaller size and ruggedness. Applications for these detectors are numerous and include life sciences, nuclear medicine, particle physics, microscopy and general instrumentation. With SPM devices, many geometrical and device parameters can be adjusted to optimize their performance for a particular application. In this paper, Monte Carlo simulations and experimental results for 1mm2 SPM structures are reported. In addition, trade-offs involved in optimizing the SPM in terms of the number and size of pixels for a given light intensity, and its affect on the dynamic range are discussed.

Characterization of novel active area silicon avalanche photodiodes operating in the Geiger mode

We present a method for characterizing avalanche photodiode (APD) photon-counting detector efficiency as a function of active area. Various shallow-junction silicon APDs having a novel active area were manufactured and tested. We show that cylindrical and checkquerboard-shaped active areas have dark counts two orders of magnitude lower than standard circular devices with an equivalent active area. A parallel implementation of small active areas creates gettering sites for defects to migrate to, which is believed to create relatively defect-free active areas as the perimeter-to-area ratio is increased. However, a compromise between a large perimeter-to-area ratio and a structure useful for practical applications must be considered to optimize the detector.

Simulation of Dark Count in Geiger Mode Avalanche Photodiodes

Silicon avalanche photodiodes operated above breakdown, in Geiger mode, can be sensitive enough to allow single photon detection. An inherent limit to GMAPD sensitivity is the noise caused by thermally generated carriers. This noise manifests itself as extraneous counts in the absence of light and is termed the dark count. The presence of the dark count in GM-APD detectors reduces the signal to noise ratio and increases the integration times that are necessary for photon detection. A 1-Dimensional model of the dark count in GM-APD detectors was developed and dark count was found to depend predominantly on carrier generation through Shockley-Read-Hall (SRH) generation centres and secondly on thermal diffusion of minority carriers in the bulk. Simulations performed show that minimisation of the dark count is limited by bulk diffusion of minority carriers. The reduction of process induced damage minimises the dark count and allows theoretically minimum dark counts to be achieved.

Process monitoring and defect characterization of single photon avalanche diodes

Silicon p-n junctions fabricated in a CMOS compatible process can be operated above breakdown in Geiger mode. Geiger mode operation allows for single photon detection. These devices are known as single photon avalanche diodes (SPAD). SPAD quality can be assessed by the dark count present during Geiger mode operation. Higher dark counts have been attributed to defects within the shallow p-n junction. While higher dark counts are detrimental to SPAD operation, the variance in dark count due to defects makes them suitable for monitoring the junction quality of a CMOS process. At present, the dark count of a SPAD is a qualitative measure of the presence of defects within the junction of a diode. The SPAD geometry does not allow the extraction of the necessary terms to fully characterize the SPAD. This prevents quantitative process characterization to be made. Special test structures and test methodologies have been designed to allow for the extraction of the parameters characterizing SPADs. The test characterization and methodology required to extract the SPAD parameters are shown. In addition, it is shown that with suitable test structures, SPADs can be characterized and used as process and device monitors in a CMOS process.

Defect passivation and dark count in Geiger-mode avalanche photodiodes

An experimental study of post metal anneal conditions on dark count in Geiger-mode avalanche photodiodes (GM-APD) has been performed. The GM-APD structure will be shown to be extremely sensitive to post-metal anneals. Dark counts from measured samples decreased by a factor of two for each separate anneal in forming gas using temperatures from 425/spl deg/C to 450/spl deg/C. Conversely anneals of 250/spl deg/C in ambient increased dark count for temperature cycles up to 124 hours. Passivation and de-passivation of defect sites within the shallow junction active area are suspected as mechanisms contributing to the variations in dark count.

Characterization of large area SPAD detectors operated in avalanche photodiode mode

Summary form only given. Single photon avalanche diodes (SPAD) have found varied applications. The dark count of a Geiger mode detector increases with area and limits the useful size of the detector. We have shown the characterization of silicon large area SPAD detectors operated below breakdown in avalanche mode. The multiplication gain and responsivity measured were excellent for 100 /spl mu/m and 500 /spl mu/m devices. While not suitable for operation in Geiger, single photon counting mode, the large area SPAD detectors exhibit excellent device performance below breakdown.