R. W. Kelsall

University of Leeds

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Monte Carlo simulation of hole mobilities in an InGaAs/GaAs strained layer quantum well

Semiconductor Science and Technology (1992)

R. W. Kelsall R. A. Abram W. Batty Eoin P. O’Reilly

The mobility and velocity-field characteristic of holes in an In0.18Ga0.82As/GaAs strained quantum well have been obtained using a Monte Carlo simulation, for lattice temperatures of 77 K and 4.2 K. The simulation incorporates a four-band Luttinger-Kohn bandstructure calculation to account for the effects of heavy-light mixing on the subband energy dispersions and wavefunctions, intra- and inter-subband phonon scattering and intrasubband alloy scattering processes are considered. The simulated 77 K phonon limited hole mobility shows a 600% enhancement over the measured and simulated values in GaAs heterostructures, but most of this enhancement is removed by alloy scattering. At 4.2 K alloy scattering is again primarily responsible for the order of magnitude difference observed between the hole mobilities in GaAs and InGaAs quantum wells. The effect of other scattering processes-impurity, plasmon-phonon and interface roughness scattering-on the hole mobility in the InGaAs/GaAs system is also discussed.

Mobilities

10.1088/0268-1242/7/1/015

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Citations (9)

Enhanced light emission from improved homogeneity in biaxially suspended Germanium membranes from curvature optimization

Optics Express (2017)

Daniel Burt Abdelrahman Al-Attili Zuo Li Frédéric Y. Gardes Moïse Sotto

A silicon compatible light source is crucial to develop a fully monolithic silicon photonics platform. Strain engineering in suspended Germanium membranes has offered a potential route for such a light source. However, biaxial structures have suffered from poor optical properties due to unfavorable strain distributions. Using a novel geometric approach and finite element modelling (FEM) structures with improved strain homogeneity were designed and fabricated. Micro-Raman (μ-Raman) spectroscopy was used to determine central strain values. Micro-photoluminescence (μ-PL) was used to study the effects of the strain profiles on light emission; we report a PL enhancement of up to 3x by optimizing curvature at a strain value of 0.5% biaxial strain. This geometric approach offers opportunity for enhancing the light emission in Germanium towards developing a practical on chip light source.

Strain engineering

Light emission

Strain (injury)

10.1364/oe.25.022911

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Citations (12)

High performance silicon optical modulators

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (2012)

Graham T. Reed David J. Thomson Frédéric Y. Gardes Y. Hu N. Owens

In this work we present results from high performance silicon optical modulators produced within the two largest silicon photonics projects in Europe; UK Silicon Photonics (UKSP) and HELIOS. Two conventional MZI based optical modulators featuring novel self-aligned fabrication processes are presented. The first is based in 400nm overlayer SOI and demonstrates 40Gbit/s modulation with the same extinction ratio for both TE and TM polarisations, which relaxes coupling requirements to the device. The second design is based in 220nm SOI and demonstrates 40Gbits/s modulation with a 10dB extinction ratio as well modulation at 50Gbit/s for the first time. A ring resonator based optical modulator, featuring FIB error correction is presented. 40Gbit/s, 32fJ/bit operation is also shown from this device which has a 6um radius. Further to this slow light enhancement of the modulation effect is demonstrated through the use of both convention photonic crystal structures and corrugated waveguides. Fabricated conventional photonic crystal modulators have shown an enhancement factor of 8 over the fast light case. The corrugated waveguide device shows modulation efficiency down to 0.45V.cm compared to 2.2V.cm in the fast light case. 40Gbit/s modulation is demonstrated with a 3dB modulation depth from this device. Novel photonic crystal based cavity modulators are also demonstrated which offer the potential for low fibre to fibre loss. In this case preliminary modulation results at 1Gbit/s are demonstrated. Ge/SiGe Stark effect devices operating at 1300nm are presented. Finally an integrated transmitter featuring a III-V source and MZI modulator operating at 10Gbit/s is presented.

Extinction ratio

Modulation (music)

10.1117/12.2001296

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Designing short tapered waveguide adapters for Ge lasers and Ge/SiGe modulators integrated with SOI waveguides

L. Lever Z. Ikonić R. W. Kelsall

We study optical mode propagation in vertically-coupled lateral tapers, which act as mode adapters between SOI waveguides and epitaxial Ge or SiGe layers for applications in laser cavities and optical modulators. We find that the taper length at which the loss tends to zero is strongly dependent on the thickness of the epitaxial layer, and we describe designs for modified tapers, which act as efficient mode adapters and are significantly shorter than linear tapers.

Waveguide

Integrated Optics

10.1109/group4.2012.6324101

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Far-infrared (THz) electroluminescence from Si/SiGe quantum cascade heterostructures

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (2003)

Stephen A. Lynch Douglas J. Paul Robert Bates David J. Norris A.G. Cullis

There is strong interest in the development of sources that emit radiation in the far infrared (1-10 THz) frequency range for applications which include early detection of skin cancer, dental imaging, telecommunications, security scanning, gas sensing, astronomy, molecular spectroscopy, and the possible detection of biological weapons. While a number of THz sources are available, there are at present no compact, efficient, cheap and practical high-power solid-state sources such as light emitting diodes or lasers. Silicon is an excellent candidate for such a THz source since the lack of polar optical phonon scattering makes it an inherently low loss material at these frequencies. Furthermore, since over 97% of all microelectronics is presently silicon based, the realisation of a silicon based emitter/laser could potentially allow integration with conventional silicon-based microelectronics. In this paper THz electroluminescence from a Si/SiGe quantum cascade structure operating significantly above liquid helium temperatures is demonstrated. Fourier transform infrared spectroscopy was performed using step scan spectrometer with a liquid helium cooled Si-bolometer for detection. Spectra are presented demonstrating intersubband electroluminescence at a number of different frequencies. These spectral features agree very well with the theoretically calculated intersubband transitions predicted for the structure.

Silicon-germanium

10.1117/12.463738

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Intersubband lifetimes inp−Si∕SiGeterahertz quantum cascade heterostructures

Physical Review B (2005)

R. W. Kelsall Z. Ikonić P. Murzyn C. R. Pidgeon P. J. Phillips

Time-resolved studies of the dynamics of intersubband transitions are reported in three different strain symmetrized $p\text{\ensuremath{-}}\mathrm{Si}∕\mathrm{Si}\mathrm{Ge}$ multiple-quantum-well and quantum cascade structures in the far-infrared wavelength range (where the photon energy is less than the optical phonon energy), utilizing the FELIX free-electron laser. The calculated rates for optical and acoustic phonon scattering, alloy disorder scattering, and carrier-carrier scattering have been included in a self-consistent energy balance model of the transient far-infrared intersubband absorption, and show good agreement with our degenerate pump-probe spectroscopy measurements in which, after an initial rise time determined by the resolution of our measurement, we determine decay times ranging from $\ensuremath{\sim}2\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}\ensuremath{\sim}25\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ depending on the design of the structure. In all three samples the lifetimes for the transition from the first light hole subband to the first heavy hole subband are found to be approximately constant in the temperature range $4--100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.

Photon energy

10.1103/physrevb.71.115326

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Citations (28)

Modulation of the absorption coefficient at 13 μm in Ge/SiGe multiple quantum well heterostructures on silicon

Optics Letters (2011)

L. Lever Y. Hu M. Myronov X. Liu N. Owens

We report modulation of the absorption coefficient at 1.3 μm in Ge/SiGe multiple quantum well heterostructures on silicon via the quantum-confined Stark effect. Strain engineering was exploited to increase the direct optical bandgap in the Ge quantum wells. We grew 9 nm-thick Ge quantum wells on a relaxed Si0.22Ge0.78 buffer and a contrast in the absorption coefficient of a factor of greater than 3.2 was achieved in the spectral range 1290–1315 nm.

Modulation (music)

Electro-absorption modulator

Quantum-confined Stark effect

10.1364/ol.36.004158

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Citations (55)

SiGe/Si quantum cascade structures deposited by low-energy plasma-enhanced CVD

Giovanni Isella Guy Matmon A. Neels E. Müller Marco Califano

Si _0.5 Ge _0.5 /Si quantum cascade structures have been deposited by low-energy plasma-enhanced CVD according to a bound-to-continuum design and characterized by high resolution x-ray diffraction and transmission electron microscopy. Electroluminescence from the active region is peaked around 2.5 THz (~10 meV) and exhibits Stark shift and polarization dependence.

10.1109/group4.2008.4638086

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Monte Carlo study of self-heating in nanoscale devices

Journal of Computational Electronics (2012)

Toufik Sadi R. W. Kelsall Neil J. Pilgrim Jean‐Luc Thobel F. Dessenne

10.1007/s10825-012-0395-x

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Citations (20)

Population inversion in optically pumped asymmetric quantum well terahertz lasers

Journal of Applied Physics (1997)

P. Harrison R. W. Kelsall

Intersubband carrier lifetimes and population ratios are calculated for three- and four-level optically pumped terahertz laser structures. Laser operation is based on intersubband transitions between the conduction band states of asymmetric GaAs-Ga1−xAlxAs quantum wells. It is shown that the carrier lifetimes in three-level systems fulfill the necessary conditions for stimulated emission only at temperatures below 200 K. The addition of a fourth level, however, enables fast depopulation of the lower laser level by resonant longitudinal optical phonon emission and thus offers potential for room temperature laser operation.

Population inversion

Optical Pumping

10.1063/1.365310

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Citations (42)