Resonant cavity quantum efficiency enhancement for near-infrared (NIR) detection in silicon detectors has been
extensively reported over the last several years. Cavity thickness uniformity has been achieved mainly by using silicon
on insulator (SOI) as starting material. Though this approach yields excellent response uniformity, it lacks the flexibility
of controlling the tuning wavelength and it is not suitable for processing in standard silicon CMOS technology.
Silicon Geiger avalanche Photodiode (GPD) technology with its single-photon sensitivity and nanosecond integration
time has seen accelerated development worldwide due to increased availability and lower cost of silicon processing.
However, the technology of fabricating large GPD arrays is being developed at a slower pace, mainly due to the need to
customize the readout circuitry (ROIC) to the application (counting, ranging or timing). We are developing the
technology to fabricate single-photon, silicon GPD arrays in standard CMOS assembled in flip-chip with dedicated
ROIC arrays and add resonant cavity enhancement (RC-GPD) to enhance their response to NIR photons. For
manufacturability, processing cost, and process flexibility reasons, we implement the resonant cavity process at the end
of the GPD+ROIC array fabrication.
We have reviewed at the SPIE DSS 2011 conference the silicon RC-GPD array technology developed at aPeak and have
pointed to the design and technological challenges to achieve uniform quantum efficiency response in NIR over large
GPD arrays. In this paper, we present the progress on tuning the resonant cavity over large RC-GPD arrays as well as the
functional validation of 32x32pixel ROICs designed to operate with such arrays. We also present the radiation hardness
data of the silicon GPD array technology (legacy technology used for RC-GPD fabrication) to proton and neutron
Single-photon imaging in infrared will add a new valuable tool to night imaging cameras. Despite years of development,
high-sensitivity SWIR cameras are still expensive and not ready for large-volume production. Germanium (Ge) is a
promising semiconductor to convert SWIR radiation and it has seen extensive development in conjunction with highspeed
We are demonstrating a new low-light level infrared array technology based on the single-photon sensitive Geiger
avalanche PhotoDiode (Si-GPD) array technology developed at aPeak and low-dislocation Germanium processing
developed at MIT. The core of the imaging camera is a Ge:Si photon-counting GPD pixel with CMOS readout. The
primary technology objective is to demonstrate through prototyping and semiconductor process development the
technical feasibility of single-photon detection cameras sensitive in the SWIR and set the performance specifications.
We report on prototype Ge:Si structures compatible with the GPD operation and technology. We demonstrate >80%
quantum efficiency at 1310nm and 45%-60% quantum efficiency at 1550nm. Dark current measurements indicate that
single-photon sensitivity (2.6x10-18W/pixel) is achievable by cooling the detector at cryogenic temperatures down to
A digital developed to provide adjustable dynamic range and frame rate is reported. Because the GPD detectors have
intrinsic excellent gating and ranging capability, the pixel architecture is developed to enable the dual mode operation -
passive illumination two-dimensional imaging (night vision) and active illumination three-dimensional imaging.
Deep Space Optical Communications (DSOC)) impose challenging requirements on detector sensitivity and bandwidth
. The current state-of-the art of high-repetition rate, high-power lasers recommends using near-infrared (NIR) 1064nm
wavelengths for specific DSOC tasks . Large photonic arrays with integrated beam acquisition, tracking and/or
communication capabilities, and smart pixel architecture should allow the implementation of more reliable and robust
DSOC systems. Integration of smart pixel technology for parallel data read, acquisition and processing is currently
available in silicon. Therefore it would be desirable to monolithically integrate the photodetectors with the electronics.
However, silicon has a weak absorption at 1064nm. One elegant approach to increase its absorption efficiency is to trap
the photons inside the silicon using the cavity resonance effect (resonant cavity enhancement or RCE).
We present in this paper the challenges of developing resonant cavity single-photon detector arrays for applications to
DSOC. The metrics of the main process parameters to fabricate resonant cavity detectors is analyzed and critical process
steps are developed and evaluated.
We conclude that such detector arrays are feasible using current state-of-the-art CMOS technology, provided that
suitable process control protocols are developed. We report a 10X performance enhancement at NIR wavelengths for the
first generation of resonant cavity single-photon detector prototypes, less than 150ps timing performance in photonstarved
mode and 20-30ps for multi-photon hits.
We have developed low-cost LADAR imagers using photon-counting Geiger avalanche photodiode (GPD) arrays, signal
amplification and conditioning interface with integrated active quenching circuits (AQCs) and readout integrated circuit
(ROIC) arrays for time to digital conversion (TDC) implemented in FPGA. Our goal is to develop a compact, low-cost
LADAR receiver that could be operated with room temperature Si-GPD arrays and cooled InGaAs GPD arrays. We
report on architecture selection criteria, integration issues of the GPD, AQC and TDC, gating and programmable features
for flexible and low-cost re-configuration, as well as on timing resolution, precision and accuracy of our latest LADAR designs.
The gamma-ray large area space telescope (GLAST) mission is planned as the next major challenge in high-energy astrophysics. FiberGLAST is one of the technologies being developed for GLAST and is using arrays of scintillation fibers for the pair-tracking and calorimeter detectors. The instrument requires optical detectors with high gain, low cost, and low power to read out the large number of individual fibers.
Thick segmented scintillating converters coupled to optical imaging detectors offer the advantage of large area, high stopping power sensors for high energy x-ray digital imaging. The recent advent of high resolution and solid state optical sensors such as amorphous silicon arrays and CCD optical imaging detectors makes it feasible to build large, cost effective imaging arrays. This technology, however, shifts the sensor cost burden to the segmented scintillators needed for imaging. The required labor intensive fabrication of high resolution, large area hard x- ray converters results in high cost and questionable manufacturability on a large scale. We report on recent research of a new segmented x-ray imaging converter. This converter is fabricated using vacuum injection and crystal growth methods to induce defect free, high density scintillating fibers into a collimator matrix. This method has the potential to fabricate large area, thick segmented scintillators. Spatial resolution calculations of these scintillator injected collimators show that the optical light spreading is significantly reduced compared to single crystalline scintillators and sub-millimeter resolution x- ray images acquired with the segmented converter coupled to a cooled CCD camera provided the resolution to characterize the converter efficiency and noise. The proposed concept overcomes the above mentioned limitations by producing a cost-effective technique of fabricating large area x-ray scintillator converters with high stopping power and high spatial resolution. This technology will readily benefit diverse fields such as particle physics, astronomy, medicine, as well as industrial nuclear and non-destructive testing.
We are developing a large area structured CsI(Tl) imaging sensor for macro-molecular x-ray crystallography for use with both intense synchrotron sources and rotating-anode laboratory x- ray sources. The CsI(Tl) scintillator is grown on a specially designed optical substrate. Our work has produced x-ray sensors with up to 70% more light output, orders of magnitude faster decay time response, and greater spatial resolution (15% MTF at 20 lp/mm) than Gd<SUB>2</SUB>O<SUB>2</SUB>S screens currently used in CCD-based detectors for biological structure determination. These advances in performance will address some of the limitations of existing area detector technology. Performance measurements for a prototype CsI(Tl) scintillator are presented. With these new sensors the development of larger area x-ray crystallography detectors with millisecond data acquisition capabilities and high spatial resolution, suitable for synchrotron applications will be possible.
Avalanche photodiodes (APDs) are solid state devices having an internal signal gain which gives them a better signal-to-noise ratio than standard photodiodes. Although they have been studied for years, recent advances in the fabrication techniques have allowed the construction of multielement arrays (up to 10 X 10) with high performance capability. This progress has resulted in increased potential for exploiting the advantages of APDs in a variety of important applications including measurements requiring fast response such as nuclear and high energy physics research, industrial nondestructive testing, medical instrumentation, and biomedical research using low energy particles. Recent experimental data characterizing APDs and APD arrays used as x-ray, particle, and low level light detectors are presented.