We report the avalanche properties of InAs avalanche photodiodes (APDs), extracted from avalanche gain and excess noise measurements performed under pure electron and pure hole injections, and from Monte Carlo simulations. For a given avalanche width electron initiated gain was found to be significantly higher than conventional InP and Si APDs. Hole initiated multiplication was negligible confirming the electron only multiplication process within the field range covered. Excess noise measurements showed the excess noise factors of less than 2, providing further evidence of the ideal avalanche properties in InAs. Monte Carlo simulations performed provided good agreement to experimental results.
A study of leakage currents and X-ray photon counting using GaAs p-i-n diodes is presented. Different fabrication techniques have been investigated, namely He implantation, partial wet etching and full wet etching. It was found that the partially etched diodes showed well-defined spectral peaks when exposed to a 55 Fe radioisotope source and uniformly low leakage currents ideal for X-ray detector arrays.
In this work we evaluated a number of QDIPs with different spectral shapes and each covering different wavelength ranges as detector candidate for implementation of an Algorithmic IR Spectrometer (AIRS). Our QDIPs have 30 to 80 dot-in-a-well (DWELL) stacks.
Quantum dot infrared photodetectors (QDIP) have established themselves as promising devices for detecting infrared (IR) radiation for wavelengths <20μm due to their sensitivity to normal incidence radiation and long excited carrier lifetimes. A limiting factor of QDIPs at present is their relatively small absorption volume, leading to a lower quantum efficiency and detectivity than in quantum well infrared photodetectors and mercury cadmium telluride based detectors. One means of increasing the absorption volume is to incorporate a greater number of quantum dot (QD) stacks, thereby increasing the probability of photon capture. Growth of InAs/InGaAs dot-in-a-well (DWELL) QDIPs with greater than 10 stacks is challenging due to the increased strain between layers, leading to high dark current. It is known that strain can be reduced in QDIPs by reducing the width of the InGaAs well and incorporating a second well consisting of GaAs and barriers consisting of AlGaAs. A number of InAs/InGaAs/GaAs DWELL QDIPs with 30-80 stacks have been grown, fabricated and characterised. Dark current in these layers appears to be constant at given electric field, suggesting strain does not increase significantly if the number of QD stacks is increased. IR spectral measurements show well defined peaks at 5.5μm, 6.5μm and 8.4μm. In this work a comparison between dark current, noise, gain, responsivity and detectivity in these layers is presented and compared to existing data from conventional DWELL QDIPs.
Much effort has been committed to development of quantum-dot-based infrared photodetectors owing to their potential for normal-incidence absorption and low dark current. Quantum-dot-in-well structures offer additional advantages, such as better wavelength tunability and improved carrier collection. This system presents a challenge for modeling of electronic structure, as it requires solution for a complex system (quantum dot plus quantum well) with both discrete levels and the continuum energy spectrum. The Green's function method, mostly used for such problems, has very high computational cost. Here we use the Finite Element Method to model intraband absorption spectra of quantum-dot-in-well structures within the effective mass approximation.
Ge on Si SPAD devices hold promise for cost effective use in vehicular LIDAR [1], quantum optics, quantum communications, and other applications. Previous Ge on SI SPAD devices using mesa structures have shown high dark count rate (DCR) and low single photon detection efficiency (SPDE) [2]. The novel planar device design demonstrated here shows low DCR and high SPDE at short-wave infrared wavelengths. The novel design allows better performance by confining the high field regions using an implanted charge sheet and small top contact region. This design removes the interaction between etched sidewalls and high electric fields seen in mesa devices. We have fabricated devices with a 100 μm diameter charge sheet and a 90 μ m diameter top contact. TCSPC measurements were taken at 78 K, 100 K, 125 K, using 1310 nm light with <; <; 1 photon per pulse on average and 50 ns gate times (Fig. 1). A record high SPDE of 38% for Ge-on-Si SPADs was measured for a device temperature of 125 K with an excess bias of 5.5 %, and a record low NEP of 2× 10 -16 WHz -1/2 was demonstrated at 78 K.
Ge-on-Si single-photon avalanche diode (SPAD) detectors have demonstrated a high single-photon detection efficiency of 38% at a wavelength of 1310 nm when operated at a temperature of 125 K.These devices exhibit reduced afterpulsing compared to InGaAs/InP SPADs under nominally identical operating conditions.Index Terms-germanium on silicon
Results from the development of substrate illuminated planar Ge on Si Single Photon Avalanche Diodes (SPAD) imaging arrays will be presented operating at short wave infrared wavelengths. Simulations have been used to optimize the designs aiming to reduce dark count rates and increase the number of absorbed photons aiming for Pelter cooler operation whilst also minimizing cross talk. To date the highest performance of Ge on Si SPADs has been demonstrated at 125 K with 38% single photon detection efficiencies and a noise equivalent power of 8e-17 W/√Hz. Surface illuminated devices have demonstrated single photon detection efficiencies up to 38% for 1 μm thick Ge absorbers and the present work will present results from 2 μm and 3 μm thick Ge absorbers aiming to increase the absorption of incident photons. The paper will describe the compromises between absorbing more photons compared to dark count rates and jitter. Examples of single photon LiDAR applications at 1310 to 1550 nm will be presented and the performance from Ge on Si SPADs will be compared to InGaAs SPAD technology in terms of single photon detection efficiency, dark count rates, afterpulsing, jitter and operating temperatures. Afterpulsing measurements demonstrate significant reductions compared to InGaAs SPADs operated under nominally identical conditions by a factor of 5 to 10. The performance of the surface illuminated SPADs in linear mode as avalanche photodetectors will also be presented. Operation at 1550 nm wavelengths at room temperature has demonstrated responsivities at unity gain of 0.41 A/W, maximum avalanche gain of 101 and an excess noise factor of 3.1 at a gain of 20 for 50 μm diameter photodetectors.
Single-Photon Avalanche Diode (SPAD) detectors are of significant interest for a range of applications [1] , in particular for quantum technologies (e.g. quantum-key distribution, quantum information processing), and light detection and ranging (LIDAR) for defence, terrain mapping, and autonomous vehicles. These applications either require, or benefit from, operation at wavelengths in the short-wave infrared (SWIR). Previous SWIR single-photon LIDAR has typically used InGaAs/InP SPAD detector technology, which has relatively low efficiency and suffers from afterpulsing. Previously, a pseudo-planar design for a Ge-on-Si SPAD was demonstrated [2] , yielding a huge improvement in performance for Ge-on-Si SPADs at 1310 nm and demonstrating the potential for Si foundry compatible SWIR SPADs. Furthermore, reduced afterpulsing was demonstrated compared to a commercial InGaAs/InP device when measured in nominally identical conditions. Here we present a further step change in performance, with reduced dark count rate (DCR), record low noise-equivalent-power (NEP) and low jitter by scaling the technology and developing 26 µm diameter pixels [3] .
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
'/%3e%3cuse xlink:href='%23a' transform='translate(0 -400)'/%3e%3cuse xlink:href='%23a' transform='translate(0 -600)'/%3e%3cuse xlink:href='%23a' transform='translate(0 -800)'/%3e%3cuse xlink:href='%23a' transform='translate(0 -1000)'/%3e%3cuse xlink:href='%23a' transform='translate(0 -1200)'/%3e%3cpath d='M0 0h1400v800H0z' style='fill:%23010066'/%3e%3cpath d='M576 100c-166.146 0-301 134.406-301 300s134.854 300 301 300c60.027 0 115.955-17.564 162.927-47.783-27.353 9.44-56.71 14.602-87.271 14.602-147.327 0-266.897-119.172-266.897-266.01 0-146.837 119.57-266.01 266.897-266.01 32.558 0 63.746 5.815 92.602 16.468C696.217 118.91 638.305 100 576 100z' style='fill:%23fc0'/%3e%3cpath d='m914.286 471.429-99.538-53.25 29.43 108.982-66.575-91.165-20.77 110.96-20.428-111.024-66.857 90.96L699.314 418l-99.701 52.943 74.065-85.192-112.8 4.441 103.694-44.62-103.555-44.94L673.8 305.42 600 220l99.538 53.25-29.43-108.982 66.575 91.165 20.77-110.96 20.428 111.023 66.857-90.959L814.97 273.43l99.702-52.944-74.065 85.193 112.8-4.441-103.694 44.62 103.555 44.94-112.785-4.79z' style='fill:%23fc0' transform='matrix(1.2738 0 0 1.2423 -89.443 -29.478)'/%3e%3c/svg%3e)
