Douglas J Paul

Douglas J Paul
University of Glasgow | UofG · James Watt School of Engineering

MA PhD CEng CPhys
My research is mainly on developing a chip-scale quantum navigator, MEMS gravimeters and short wave infrared SPADs.

About

366
Publications
40,835
Reads
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5,325
Citations
Introduction
Douglas Paul FRSE FInstP has an MA degree in Physics and Theoretical Physics and a PhD from the Cavendish Laboratory, University of Cambridge. He presently holds a Royal Academy of Engineering Research Chair in Emerging Technologies. His research interests include silicon nanowires, quantum technologies (MEMS gravimeters, micro cold atom systems, Ge on Si single photon avalanche detectors), integrated mid-infrared sensors and SiGe THz quantum cascade lasers.
Additional affiliations
January 1994 - August 2007
University of Cambridge
Position
  • PostDoc Position
Description
  • I ran all the SiGe and Si device research in the Semiconductor Physics Group
Education
October 1990 - December 1993
University of Cambridge
Field of study
  • Physics
October 1987 - June 1990
University of Cambridge
Field of study
  • Natural Science - Physics and Theoretical Physics

Publications

Publications (366)
Preprint
Full-text available
This paper describes a temperature sensitivity or thermal sag measurement of a geometric anti-spring based micro-electromechanical system (MEMS) gravimeter (Wee-g). The Wee-g MEMS gravimeter is currently fabricated on a (100) silicon wafer using standard micro-nano fabrication techniques. The thermal behavior of silicon indicates that the Young's m...
Article
Laser cooled atoms have proven transformative for precision metrology, playing a pivotal role in state-of-the-art clocks and interferometers and having the potential to provide a step-change in our modern technological capabilities. To successfully explore their full potential, laser cooling platforms must be translated from the laboratory environm...
Preprint
Full-text available
Laser cooled atoms have proven transformative for precision metrology, playing a pivotal role in state-of-the-art clocks and interferometers, and having the potential to provide a step-change in our modern technological capabilities. To successfully explore their full potential, laser cooling platforms must be translated from the laboratory environ...
Article
Full-text available
The measurement of tiny variations in local gravity enables the observation of subterranean features. Gravimeters have historically been extremely expensive instruments, but usable gravity measurements have recently been conducted using MEMS (microelectromechanical systems) sensors. Such sensors are cheap to produce, since they rely on the same fab...
Article
The integration of Ge on Si for photonics applications has reached a high level of maturity: Ge photodetectors are available on the Si platform in foundry processes, and Si/Ge heterostructure multiple quantum-well photodiodes are rapidly progressing towards applications in light modulation. These successes result from decades of development of high...
Article
Full-text available
The design, fabrication, and characterization of a silicon nitride waveguide polarization rotator and polarization beam splitter that operate with a polarization extinction ratio (PER) of ∼30 dB at the rubidium atomic transition of 780 nm wavelength are demonstrated. These polarization devices are fabricated on the same chip using a self-aligned pr...
Conference Paper
A silicon nitride waveguide polarization rotator and polarization beam splitter that operate with a polarization extinction ratio close to 30 dB at the rubidium atomic transition of 780 nm wavelength are demonstrated.
Article
The emergence of a photonic band gap in Ge-on-Si micropillars ordered in a two-dimensional square lattice is demonstrated by the finite-element method. Candidate architectures are fabricated through epitaxy and the opening of the photonic band gap experimentally proved by photoluminescence spectroscopy. When the direct-gap emission of Ge is resonan...
Article
Full-text available
Germanium-on-Silicon (Ge-on-Si) based single-photon avalanche diodes (SPADs) have recently emerged as a promising detector candidate for ultra-sensitive and picosecond resolution timing measurement of short-wave infrared (SWIR) photons. Many applications benefit from operating in the SWIR spectral range, such as long distance Light Detection and Ra...
Preprint
Full-text available
The measurement of tiny variations in local gravity enables the observation of subterranean features. Gravimeters have historically been extremely expensive instruments, but usable gravity measurements have recently been conducted using MEMS (microelectromechanical systems) sensors. Such sensors are cheap to produce, since they rely on the same fab...
Article
Full-text available
The development of three-dimensional architectures in semiconductor technology is paving the way to new device concepts for various applications, from quantum computing to single photon avalanche detectors. In most cases, such structures are achievable only under far-from-equilibrium growth conditions. Controlling the shape and morphology of the gr...
Article
Full-text available
Unveiling the spatial and temporal dynamics of a light pulse interacting with nanosized objects is of extreme importance to widen our understanding of how photons interact with matter at the nanoscale and trigger physical and photochemical phenomena. An ideal platform to study light–matter interactions with an unprecedented spatial resolution is re...
Article
Full-text available
We report electroluminescence originating from L-valley transitions in n-type Ge/Si0.15Ge0.85 quantum cascade structures centered at 3.4 and 4.9 THz with a line broadening of Δ f / f ≈ 0.2. Three strain-compensated heterostructures, grown on a Si substrate by ultrahigh vacuum chemical vapor deposition, have been investigated. The design is based on...
Preprint
Full-text available
A single-axis Microelectromechanical system gravimeter has recently been developed at the University of Glasgow. The sensitivity and stability of this device was demonstrated by measuring the Earth tides. The success of this device was enabled in part by its extremely low resonant frequency. This low frequency was achieved with a geometric anti-spr...
Preprint
Full-text available
We report electroluminescence originating from L-valley transitions in n-type Ge/Si$_{0.15}$Ge$_{0.85}$ quantum cascade structures centered at 3.4 and 4.9 THz with a line broadening of $\Delta f/f \approx 0.2$. Three strain-compensated heterostructures, grown on a Si substrate by ultrahigh vacuum chemical vapor deposition, have been investigated. T...
Article
The performance of planar geometry Ge-on-Si single-photon avalanche diode detectors of 26µm diameter is presented. Record low dark count rates are observed, remaining less than 100 K counts per second at 6.6% excess bias and 125 K. Single-photon detection efficiencies are found to be up to 29.4%, and are shown to be temperature insensitive. These p...
Article
Full-text available
Knowledge of the spatio-temporal changes in the characteristics and distribution of subsurface fluids is key to properly addressing important societal issues, including: sustainable management of energy resources (e.g., hydrocarbons and geothermal energy), management of water resources, and assessment of hazard (e.g., volcanic eruptions). Gravimetr...
Conference Paper
The mid-infrared spectral region is key to several large market applications such as security, healthcare and environmental monitoring. This is due to how chemical compounds can be detected from unique vibrational modes that absorb in the molecular 'fingerprint' region (6.7-20 m wavelength). There is significant interest in realizing cheaper and sm...
Conference Paper
There is an ever-growing need for compact sources which can be used for the cooling process in high accuracy atomic clocks. Current systems make use of large, expensive lasers which are power-hungry and often require frequency doubling in order to hit the required wavelengths. Distributed feedback (DFB) lasers have been fabricated at a number of ke...
Article
Full-text available
A distributed feedback GaAs-based semiconductor laser with a laterally coupled grating is demonstrated at a wavelength of 780.24 nm with up to 60 mW power. A mode expander and aluminum-free active layers have been used to reduce the linewidth to 612 kHz while maintaining high output power. The laser demonstrates over 40 dB side-mode suppression rat...
Article
Full-text available
A novel spectroscopy technique to enable the rapid characterization of discrete mid-infrared integrated photonic waveguides is demonstrated. The technique utilizes lithography patterned polymer blocks that absorb light strongly within the molecular fingerprint region. These act as integrated waveguide detectors when combined with an atomic force mi...
Conference Paper
Ge-on-Si single photon avalanche diodes are used to demonstrate LIDAR in laboratory conditions. Modelling demonstrates that eye-safe kilometre range-finding is achievable at 1450nm wavelength. Afterpulsing is found to be considerably lower than commercial InGaAs/InP devices. Single photon avalanche diode (SPAD) detectors are reverse biased diodes o...
Conference Paper
A silicon nitride micro-ring resonator with loaded Q factor of 1.4 million at 780 nm wavelength on silicon substrates for chip-scale atomic systems targeting the 87 Rb atomic transition at 780.24 nm.
Conference Paper
An ultra-broadband Ge-on-Si waveguide polarization rotator is experimentally demonstrated with a polarization extinction ratio of ≥ 15 dB over a 2 µm bandwidth (9-11 µm wavelength) with an insertion loss of ≤ 1 dB.
Conference Paper
Distributed feedback (DFB) lasers have been realized emitting at a wavelength of 780.24 nm which demonstrate powers in excess of 60 mW with 612 kHz linewidth for use in rubidium (87 Rb) cold atom systems.
Article
Full-text available
We present an experimental and theoretical analysis of the formation of nanovoids within Si micro-crystals epitaxially grown on Si patterned substrates. The growth conditions leading to the nucleation of nanovoids have been highlighted and the roles played by the deposition rate, substrate temperature, and substrate pattern geometry, are identified...
Article
Full-text available
The design, modeling, micro-fabrication, and characterization of an ultra-broadband Ge-on-Si waveguide polarization rotator are presented. The polarization rotator is based on the mode evolution approach where adiabatic symmetric and anti-symmetric tapers are utilized to convert from the fundamental transverse magnetic to electric mode. The device...
Article
Full-text available
Low loss, single mode, Ge-on-Si rib waveguides are used to demonstrated optical sensing in the molecular fingerprint region of the mid-infrared spectrum. Sensing is carried out using two spin-coated films, with strong absorption in the mid-infrared. These films are used to calibrate the modal overlap with an analyte, and therefore experimentally de...
Article
Full-text available
The waveguide losses from a range of surface plasmon and double metal waveguides for Ge/Si1-xGex THz quantum cascade laser gain media are investigated at 4.79 THz (62.6 μm wavelength). Double metal waveguides demonstrate lower losses than surface plasmonic guiding with minimum losses for a 10 μm thick active gain region with silver metal of 21 cm-1...
Article
Full-text available
A silicon nitride micro-ring resonator with a loaded Q factor of 1.4 × 106 at 780 nm wavelength is demonstrated on silicon substrates. This is due to the low propagation loss waveguides achieved by optimization of waveguide sidewall interactions and top cladding refractive index. Potential applications include laser frequency stabilization allowing...
Article
We study radiative relaxation at terahertz frequencies in n-type Ge/SiGe quantum wells, optically pumped with a terahertz free electron laser. Two wells coupled through a tunneling barrier are designed to operate as a three-level laser system with non-equilibrium population generated by optical pumping around the 1»3 intersubband transition at 10 T...
Conference Paper
We introduce a new experimental strategy to investigate the transient resonant behavior of plasmonic nanostructures. Our approach allows to access their full-time field-resolved response in amplitude and phase.
Article
Full-text available
The recently developed precession electron diffraction (PED) technique in scanning transmission electron microscopy has been used to elucidate the local strain distribution and crystalline misorientation in a CMOS fabricated strained Ge microdisk structure grown on a Si substrate. Tensile strained Ge and GeSn structures are considered to be potenti...
Article
Full-text available
n-type doped Ge quantum wells with SiGe barriers represent a promising heterostructure system for the development of radiation emitters in the terahertz range such as electrically pumped quantum cascade lasers and optically pumped quantum fountain lasers. The nonpolar lattice of Ge and SiGe provides electron-phonon scattering rates that are one ord...
Article
Full-text available
We present a scanning light detection and ranging (LIDAR) system incorporating an individual Ge-on-Si single-photon avalanche diode (SPAD) detector for depth and intensity imaging in the short-wavelength infrared region. The time-correlated single-photon counting technique was used to determine the return photon time-of-flight for target depth info...
Article
Exploiting intersubband transitions in Ge/SiGe quantum cascade devices provides a way to integrate terahertz light emitters into silicon-based technology. With the view to realizing a Ge/SiGe Quantum Cascade Laser, we present the optical and structural properties of n-type strain-symmetrized Ge/SiGe asymmetric coupled quantum wells grown on Si(001)...
Conference Paper
High-Q microring resonators have applications in gyroscopes, frequency comb generation, and feedback systems to control narrow linewidth integrated lasers [1-3]. This paper demonstrates the highest Q values measured for microring resonators at 780 nm wavelength. These sub mm integrated cavities can be used to provide an error signal for locking a d...
Conference Paper
We introduce a new experimental strategy to investigate the transient resonant behavior of plasmonic nanostructures. Our approach allows to access their full-time field-resolved response in amplitude and phase.
Article
Full-text available
The aim of this work is to evaluate whether silicon heterojunction solar cells, lacking highly emissive, heavily doped silicon layers, could be better candidates for hybrid photovoltaic thermal collectors than standard aluminium-diffused back contact solar cells. To this end, the near and mid infrared emissivity of full silicon heterojunction solar...