Stuart D. Coomber

High-performance 40nm gate length InSb p-channel compressively strained quantum well field effect transistors for low-power (VCC=0.5V) logic applications

This paper describes for the first time, a high-speed and low-power III-V p-channel QWFET using a compressively strained InSb QW structure. The InSb p-channel QW device structure, grown using solid source MBE, demonstrates a high hole mobility of 1,230 cm2/V-s. The shortest 40 nm gate length (LG) transistors achieve peak transconductance (Gm) of 510 muS/mum and cut-off frequency (fT) of 140 GHz at supply voltage of 0.5V. These represent the highest Gm and fT ever reported for III-V p-channel FETs. In addition, effective hole velocity of this device has been measured and compared to that of the standard strained Si p-channel MOSFET.

3D electronic holography display system using a 100-megapixel spatial light modulator

The display of 3D images containing all the depth cues required by the human vision system can be achieved using a reconfigurable Computer Generated Hologram (CGH) with high pixel count. Giga-pixel scale displays or spatial light modulators are required in order to form directly viewable 3-D images of 0.5m in size. A new Spatial Light Modulator (SLM) solution, Active Tiling (AT)1, has been developed by the authors to replay giga-pixel scale CGHs at video refresh rates. This has overcome a key bottleneck preventing commercial development of electro-holography to date. At the heart of an AT system is a set of replication optics which produces multiple images of an electrically addressed Spatial Light Modulator (SLM) on an optically addressed spatial light modulator (OASLM). Solutions employed within electronic holography will be discussed. A holographic 3D display system using a 4 channel Active Tiling modulator with a new replay optics system has demonstrated directly viewable 3-D images and animations from 100 Mega-pixel CGH data. This provided viewing of both horizontal parallax only (HPO) and full parallax 3-D images up to 140mm in size.

100-megapixel computer-generated holographic images from Active Tiling: a dynamic and scalable electro-optic modulator system

Giga-pixel scale displays or spatial light modulators are required in order to form directly viewable 3-D images of 0.5m in size using the principles of computer generated holography (CGH). This has been a key bottleneck preventing commercial development of electro-holography. Active Tiling is a modular spatial light modulator system developed by the authors to provide a route to replay images from giga-pixel scale CGHs. This paper will present the latest development of a multi-channel Active Tiling unit and results from this system for the first time. A holographic 3D display system using a 4 channel Active Tiling modulator with a new replay optics system has demonstrated directly viewable 3-D images and animations from 100 Mega-pixel CGH data. This provided viewing of both horizontal parallax only (HPO) and full parallax 3-D images up to 140mm in size. 25 Mega-pixels of CGH data is written by each channel onto a liquid crystal optically addressed spatial light modulator at high resolution. The modular design of Active Tiling permits CGH data to be written seamlessly across multiple channels which can be updated at rates up to 30 Hz. A Fourier Transform optical replay system was developed and integrated with the 4-channel Active Tiling system to form the CGH images.

Recent developments in computer-generated holography: toward a practical electroholography system for interactive 3D visualization

This paper will give an overview of some recent developments in electroholography for applications in interactive 3D visualisation. Arguably the ultimate technology for this task, it is the only approach having the potential to deliver full depth cue, 3D images, having resolutions beyond that which can be perceived by the human eye. Despite significant advances by many researchers, the high pixel counts required by the computer generated hologram (CGH) patterns in these systems remain daunting - in practice, systems able to calculate and display reconfigurable CGH having pixel counts of more than one billion may be required for 300 mm width, 3D images. Advances described include novel Fourier mode variants of diffraction specific algorithms and parallel binarisation techniques for design of the CGH patterns; computer architectures for effective implementation of these algorithms for interactive CGH calculation; the latest developments in the Active Tiling spatial light modulator technology and novel replay optics arrangements including folded mirror geometries, viewer tracking alternatives and new horizontal parallax configurations. Throughout, the emphasis is optimisation towards implementation as an interactive electroholography system having practical utility. Some recent results from demonstrations of aspects of the technology will be shown. These include monochrome and colour, static and dynamic, horizontal parallax only (HPO) and full parallax, 3D images, generated from true CGH systems with up to 24 billion pixels.

Midinfrared GaInSb/AlGaInSb quantum well laser diodes operating above 200 K

Electroluminescence from GaInSb/AlGaInSb type I quantum well diode lasers, grown on GaAs, has been investigated as a function of strain in the quantum wells. Lasing was observed, in pulsed operation, up to temperatures of 161, 208, 219, and 202 K for structures containing 0.55%, 0.62%, 0.78%, and 1.1% strain, respectively, with lasing occurring at ∼3.3 μm at 200 K for the 1.1% structure.

Progress and prospects for practical electroholographic display systems

Continuing advances in both computing and modulator techniques and technologies increase the likelihood of electro-holography displays becoming practical in the next five years or so. These displays aim to allow high quality, interactive, 3D images to be generated from compte held dat. Until now, large pixel counts have precluded any systems of practical utility. This paper will describe recent progress towards meeting the challenges of implementing such displays. Despite more than exponential increases in computer performance, interactive hologram calculation remains an issue. A significant part of the cost of any electro-holography product will be associated with the computational requirements. These are strongly influenced by the choice of computer generated hologram (CGH) type, the algorithm used to calculate the CGH and the computer architecture chosen for implementation. The leading optics will be discussed and some experimental results presented indicating performance, cost and image quality tradeoffs. Eventual choice will depend on the specifications of the required system. Another traditional bottleneck has been the optical modulator employed. As one of the leading candidates for practical implementation, the current and projected performance of the DERA Active Tiling system will be explored, and the latest experimental results presented. These will include the first published, full parallax, true CGH, 3D image replays from an Active Tiling channel.

Optically addressed spatial light modulators for replaying computer generated holograms

Holographic techniques offer a route to the generation of 3D images having all the depth cues used by the human vision system. A new electro-optic modulator system has been developed by the authors to replay dynamic holographic images. This Active Tiling (AT) system offers a route to replay giga-pixel computer generated holographic (CGH) images with video refresh rates. A key component of the AT system is an Optically Addressed Spatial Light Modulator (OASLM), onto which segments of the large pixel count CGH are loaded or written sequentially before the whole CGH frame is read out simultaneously. The OASLM device structure used consists of an amorphous silicon photosensor layer combined with surface stabilised ferroelectric liquid crystal (SSFLC) light modulation layer. A number of experiments have been conducted to determine the performance and suitability of this device for replaying a CGH. These experiments include electro-optic switching to determine the operating window and diffraction efficiency (DE) measurements to determine spatial resolution performance. A detailed description of the experimental apparatus and method used for measuring DE is presented, and results show the OASLM to be capable of diffracting light from fringe patterns with spatial periods as low as 3 micrometers (333 lp/mm). Examples of CGH replay of 3D images from the OASLM when operating within the AT system are also presented.

Recombination processes in midinfrared AlxIn1−xSb light-emitting diodes

Emission characteristics, spectral properties, and quantum efficiencies of AlxIn1−xSb light-emitting diodes, with aluminum compositions between 0% and 8.75%, have been investigated as a function of temperature from 25 to 300 K, and a function of current from 1 to 100 mA. As both current and temperature are varied a change in the dominant recombination mechanism is observed as indicated by changes in the measured emission. An analysis of the light-current characteristics shows that Auger processes become important in all devices at temperatures above 100 K, implying an activation energy of approximately 7–13 meV depending on the aluminum composition.

Mid-Infrared

The properties of AlxIn1-xSb light-emitting diodes (LEDs) and photodetectors have been investigated to establish their suitability for methane sensing. Using these components it is possible to achieve good signal-to-noise values at both the characteristic absorption wavelength and also at 4 ¿m, an attractive wavelength for use as a reference channel. A limit of sensitivity of approximately 400 ppm, with an integration time of 10 s and a path length of 5 cm, was estimated for methane detection.

{\rm Al}_{x}{\rm In}_{1-x}{\rm Sb}

Photoluminescence (PL) from GaInSb/AlInSb type I multi-quantum-wells, grown on GaAs, has been investigated as a function of strain in the quantum wells. Luminescence, between 3 and 4 μm, was observed for all samples, with good agreement between the measured and calculated peak emission energies. Analysis of the temperature dependence of the luminescence suggests that population of excited quantum well hole subbands occurs at high temperature, leading to a reduction in the PL signal. Room temperature luminescence was obtained from a sample with ∼0.8% strain in the quantum wells. Preliminary results from laser diodes fabricated from companion wafers indicate lasing up to 220 K.