Silicon based avalanche photodiodes (APDs) have exhibited impressive performance over the visible spectrum
for more than a decade. Photon counting with these devices has progressed to the level where room-temperature
operation and low dark count rates (< 100 <i>Hz</i>) are commonplace. Several commercial enterprises have been
established to capitalise on these devices and many niche markets are now serviced by incorporating these devices
into suitable systems. This paper describes one approach that allows the performance of silicon based Geigermode
avalanche photodiodes (GM-APDs) to be extended into the near-infra-red. The process development is
described whereby Ge absorbers are incorporated into adapted silicon APD designs to provide separate absorption
and multiplication devices. Simulation results are presented outlining the performance of these devices at
wavelengths between 1 μm and 1.6 μm.
The performance results from silicon APD designs are presented for visible wavelengths. A silicon-germanium
bonding process is described and the challenges presented in developing the hybrid absorber/multiplier structure
are detailed. Finally, a summary of appropriate custom application integrated circuits for various applications
Shallow junction silicon avalanche photodiodes developed for photon-counting applications exhibit a multiplication gain of several hundred when operated near breakdown. The small size and relatively large gain of these devices identifies them as potential candidates for short-haul optical networking at 650nm. Of importance is the frequency response of these devices and in particular the limitations on achievable bandwidth placed by the packaging of the diodes. This work investigates the effect package capacitance has on the frequency response of Geiger Mode Avalanche Photodiodes (GMAP) when compared to micro-stripline mounted devices. Impulse response measurements are made of the diode using a pulsed laser diode at a wavelength of 650 nm which provides pulses with full-width at half maximum (FWHM) of 70 ps typical and 200 ps maximum. A Fast Fourier Transform (FFT) is applied to the measured pulse to convert it to the frequency domain and de-embed the response of the test fixture and cable assembly. The electrical parameters of the packaged and micro-stripline mounted devices are compared in the frequency domain to see the effect of the package capacitance on the frequency response. Different device geometries are explored to identify suitable candidates for short-haul plastic optical fibre communications.
An active quench and reset circuit (AQRC) is an essential control circuit for ensuring high-speed photon counting with geiger-mode avalanche photodiodes (GMAPs). Its purpose is to turn off the detector when an avalanche has been detected, register a photon count and then reset the device to its quiescent bias voltage after a preset interval, to enable further avalanche events to be counted. This paper presents an AQRC-IC, developed using Europractice's ASIC Service. The purpose of the design was to develop a high-speed CMOS AQRC for hybrid integration with in-house GMAPs. The designed ASIC, developed using AMS' 3.3 V 0.35 μm CMOS process models, includes a ballast resistor for the external GMAP, a comparator sensing-stage, an active quench and an active reset stage. The hold-off time is determined using external silicon delay lines and an FPGA. The ASIC is implemented on a ceramic DIP as is the GMAP, and the AQRC prototype achieves a saturated count-rate of 5 Mcounts/s, an active quench of 45 ns, an active reset of 30 ns and possible increments of the hold-off time between 50 ns and 500 ns.
This paper describes the integration of an automatic gain and bias control circuit for avalanche photodiodes with the Sensl PCMPLusX photon counting module. The combination is a self contained module with integrated sensor, power supply, cooling and full microprocessor control system. The sensors can be configured remotely via a PC enabling the user to optimize the sensor performance for a particular application. The system has four channels which can be configured either in photon counting mode or gain control mode. With the photon counting module enabled the user can optimize detector characteristics such as quantum efficiency, dark count, amplification and operating temperature for specific applications. With the gain control module enabled the system allows the user to program the sensor to a desired multiplication gain factor and the circuit to automatically adjust for fluctuations in supply voltage.
With the increasing use of optical fibre in both the telecommunications and home networking areas, the packaging and
alignment of various optoelectronic devices has never been more
critical. In particular coupling of Plastic Optical Fibre (POF) to
detectors has become an important area of research. Most off-the-shelf POF has a core diameter of 980 micron, while a typical photodiode may have an active area diameter of 50 micron. Hence without some kind of physical alignment losses may become unmanageable. This paper describes efforts to couple Plastic
Optical Fibres to an avalanche photodiode (APD) array.
An imaging POF fibre-bundle is used to connect to the array in a
low cost versatile manner. An array of up to ten fibres is used
to form the bundle. Mechanical guide systems both on the
substrate of the chip and on the package housing itself are used
to align each individual fibre to a corresponding photodiode. The
results from several focusing techniques are presented to overcome
coupling losses encountered while focusing the beam from the POF
onto the smaller detector active area. A multi fibre connector is
used to connect other instruments at the opposite end of the fibre
bundle. The primary application of this technology will enable the
use of arrays of photon counting detectors in astronomy.
The I-V characteristics of AlGaInP/GaInP bulk and multiquantum barrier n-i-n diodes between 20 and 300 K were measured with pA current resolution. When analysed using a thermionic emission model, measured activation energies in the bulk structures were close to the expected conduction band offset. The interplay of other transport mechanisms, including Fowler-Nordheim tunneling and Poole-Frenkel emission was investigated in both the bulk and multiquantum barrier diodes. Transition points between different regimes were observed. Similarities and differences were observed for the bulk and multiquantum barrier diodes. Measured Fowler-Nordheim barrier heights in the bulk barrier diodes agree well with those derived from simulations except in the case of the indirect material at forward bias.
Considerable interest currently exists in the use of plastic optical fibre (POF) for short distances data communications. Attenuation in POF is reduced at 650 nm compared to longer wavelength light and hence silicon based photoreceivers are ideal candidates for use with POF. The difficulty with the development of a CMOS photoreceiver, however, is the realisation of a high speed CMOS photodiode. This paper presents CMOS compatible, shallow junction Geiger-mode avalanche photodiodes (GMAPs) and investigates their bandwidth at 650 nm. Various sized GMAPs (500 μm and 250 μm diameter GMAPs with 20 μm cathode-anode overlaps and 20 μm diameter GMAPs with 3 μm, 4 μm and 5 μm overlaps) were mounted on PCBs. The anodes and cathodes were
wirebonded to ground and 50Ohm transmission lines respectively. Impulse response measurements were made for each diode over a range of bias voltages, using a 650 nm picosecond pulsed laser diode. The bandwidths of each diode were calculated from the measured impulse responses and plots of bandwidth versus reverse bias were
made. The results indicate very high speed operation is possible (> 1 GHz (20 μm diameter diode)), even for large detectors (> 250 MHz (500 μm diameter diode)).
Large-area Geiger-mode avalanche photodiodes (GMAPs) that are designed to be compatible with a 1.5μm CMOS and silicon-on-insulator (SOI) CMOS process are presented here as candidate detectors for use in optoelectronic integrated circuits (OEICs). The photodetectors have 250μm and 500μm diameter active areas with 20um virtual guard ring overlaps. The GMAPs have a breakdown voltage of -30V and will be biased below breakdown in avalanche mode. The diodes' junction capacitances at 5V reverse bias are 11.66pF and 41.71pF respectively and 4.99pF and 17.95pF respectively at 27V reverse bias. The 250μm photodiode has a calculated bandwidth of 454MHz when biased at -5V while the 500μm diode has a calculated bandwidth of 142MHz when biased at -5V calculated using small-signal equivalent circuits for the devices.
This paper describes the present status and the ongoing development of a curriculum for providing a broad, but substantive introduction to
optical electronics for senior undergraduate Electrical and Electronic
Engineering students. An outline of the current course structure is
presented, along with the rationale for the topics included and the
order in which they are taught. The methods of course delivery are
evaluated and their effectiveness is discussed along with techniques for maintaining student attention and interest. Other teaching innovations, aimed at encouraging postgraduate studies in optoelectronics/photonics, include presenting topics from the optoelectronics research within the Department and offering a broad selection of final year undergraduate projects in optical electronics and photonics. To promote interest in pursuing optical electronics and photonics as a career an optical engineering professional is invited to present a guest lecture during the course. The evolution of a teaching portfolio and self-assessment, in addition to student criticism and evaluation are described. Future directions for this course are outlined, in particular the development of class-based demonstrations to enhance student learning and material comprehension.
Novel integrated sensors will be required for future detection
platforms for the measurement of fluorescence and luminescence. The
current trend towards integration of optical detectors and the broad
advances in optical emitting dyes and proteins will be combined
in robust, low-cost, point-of-use, diagnostic equipment. To this end
we are experimenting with an integrated optical hybrid sensing device which will combine a flip-chipped, array of solid-state single photon counting detectors with surface mount passive quench circuits on a conventional glass substrate. This flip-chipped arrangement both 1) increases the speed of response of the detector and 2) increases the
robustness and ease of integration and reduces single photon detector handling requirements. The potential of integrated solid-state photon detectors will be demonstrated for the real-time quantitative detection of luciferase, a light emitting protein expression reporter molecule. A 15μm solid-state Geiger-mode avalanche photodiode (APD) operating in single photon counting mode will be compared with a standard photomultiplier tube (PMT) for luciferase luminescence
detection. Detection levels of 2×10<sup>6</sup> and 1×10<sup>7</sup> enzyme molecules will be demonstrated for PMT and Geiger-mode APD respectively. The size of the Geiger-mode APD active area will be shown to be the limiting factor in luciferase signal detection for non-integrated applications. A simple geometric model will show that detection limits of 1×10<sup>4</sup> are achievable in integrated sensing platforms using room temperature operated single photon counting detectors.
New Geiger Mode Avalanche Photodiodes (GM-APD) have been designed and characterized specifically for use in microarray systems. Critical parameters such as excess reverse bias voltage, hold-off time and optimum operating temperature have been experimentally determined for these photon-counting devices. The photon detection probability, dark count rate and afterpulsing probability have been measured under different operating conditions. An active- quench circuit (AQC) is presented for operating these GM- APDs. This circuit is relatively simple, robust and has such benefits as reducing average power dissipation and afterpulsing. Arrays of these GM-APDs have already been designed and together with AQCs open up the possibility of having a solid-state microarray detector that enables parallel analysis on a single chip. Another advantage of these GM-APDs over current technology is their low voltage CMOS compatibility which could allow for the fabrication of an AQC on the same device. Small are detectors have already been employed in the time-resolved detection of fluorescence from labeled proteins. It is envisaged that operating these new GM-APDs with this active-quench circuit will have numerous applications for the detection of fluorescence in microarray systems.
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.
We report on a novel silicon-based resonant cavity photodiode with a buried silicon dioxide layer as the bottom reflector. The buried oxide is created by using a separation by implantation of oxygen technique. The device shows large Fabry-Perot oscillations. Resonant peaks and anti-resonant troughs are observed as a function of the wavelength, with a peak responsivity of about 50 mA/W at 650 nm and 709 nm. The leakage current density is 85 pA/mm<SUP>2</SUP> at -5 V, and the average zero-bias capacitance is 12 pF/mm<SUP>2</SUP>. We also demonstrate that the buried oxide prevents carriers generated deep within the substrate from reaching the top contacts, thus removing any slow carrier diffusion tail from the impulse response.
Linear arrays of single photon avalanche detectors (SPADs) designed for use in low light level imaging applications were fabricated using a novel planar process that is compatible with standard CMOS technology. The device characteristics for these arrays are presented here to investigate their suitability for high efficiency low light level imaging. A new scheme is proposed to eliminate the problem of optical crosstalk between pixels in the array by introducing a trench isolation process coupled with silicon-on-insulator (SOI) technology.
Linear arrays of single photon avalanche detectors (SPADs), fabricated using a novel planar process that is compatible with CMOS technology, are presented here. Their suitability for application in fluorescence correlation spectroscopy (FCS) is investigated by examining characteristics such as the dark counting rate, breakdown voltage and quantum efficiency. The problem of optical crosstalk between pixels in the array is investigated and a trench isolation process is proposed to eliminate crosstalk between adjacent pixels in the array.
An extended effective mass model is developed to account for the possibility of mixing of the electron wave function from the Γ conduction-band state to the <i>X</i> conduction-band state. The strength of the mixing is determined by a mixing parameter Δ in association with the assumption of a finite interface thickness. For a simple quantum well, the model Δ compares favorably with more complicated empirical pseudopotential models, featuring complete descriptions of the band structure. A multiquantum barrier (MQB) has been designed. Using the single-band effective mass approximation model, for use in visible laser diode structures for enhanced electron confinement, it is clear that within the limitations of the model when mixing effects are accounted for, the degradation in performance is negligible. The MOB design compared with a single barrier of equivalent thickness shows a doubling of the electron reflection coefficient.