Showing papers by "Neil Gordon published in 2006"
TL;DR: In this article, the room-temperature electroluminescent properties of InSb/AlxIn1-xSb quantum-well light-emitting diodes were investigated.
Abstract: We have investigated the room-temperature electroluminescent properties of InSb/AlxIn1-xSb quantum-well light-emitting diodes. The maximum emission from diodes containing quantum wells occurred at significantly higher energies than the band gap of InSb. Close agreement between experimental and theoretical data confirms that recombination occurs within the quantum well.
27 citations
TL;DR: In this article, an approach for producing two-dimensional arrays based on biasing the detector elements at close to zero bias so that the 1/f noise is minimized is described and an example of the imaging performance is shown.
Abstract: This paper reports progress with work aimed at using HgCdTe detector arrays at temperatures above 200 K where cooling is possible with thermo-electric coolers. Both theoretical analysis and calculations based on the detector dark currents indicate that useful performance should be obtainable in this temperature range. However, measurements on the performance of two-dimensional arrays show that the thermal sensitivity degrades rapidly for temperatures above 200 K. The reduction in performance at higher temperatures is shown to be mainly due to increasing 1/f noise as the temperature increases. The noise is characterized as a function of bias and temperature and this is used to predict the noise equivalent temperature difference (NETD) as a function of temperature. We describe an approach for producing two-dimensional arrays based on biasing the detector elements at close to zero bias so that the 1/f noise is minimized. A camera based on this concept is described and an example of the imaging performance is shown.
14 citations
01 Sep 2006
TL;DR: The Kull-back divergence is extensively used to compare estimated distributions, and methods with ability to express non-Gaussian posterior distributions are shown to give superior performance over classical second-order moment based estimators.
Abstract: Performance for filtering problems is usually measured using the second-order moment. For non-Gaussian applications, this measure is not always sufficient. In this paper, the Kull-back divergence is extensively used to compare estimated distributions. Several estimation techniques are compared, and methods with ability to express non-Gaussian posterior distributions are shown to give superior performance over classical second-order moment based estimators.
12 citations
TL;DR: CdxHg1−xTe layers with bandgap in the midwavelength infrared (MWIR) and long-wavelength IR (LWIR) regions were grown by molecular beam epitaxy, and one-dimensional and two-dimensional (2D) arrays of planar photodiodes were fabricated by ion milling of vacancy-doped layers as discussed by the authors.
Abstract: CdxHg1−xTe layers with bandgap in the mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) regions were grown by molecular beam epitaxy, and one-dimensional (1D) and two-dimensional (2D) arrays of planar photodiodes were fabricated by ion milling of vacancy-doped layers. The grown layers have varying densities of needle-shaped structures on the surface. The needles are not associated with twins or dislocations in the layers, but could instead be due to (111) facets being reinforced by a preferential Te diffusion direction over steps on the surface. The needles do not seem to affect diode quality. 64 element 1D arrays of 26×26 μm2 or 26×56 μm2 diodes were processed, and zero-bias resistance-times-area values (R0A) at 77 K of 4×106 Ω cm2 at cutoff wavelength λCO=4.5 μm were measured, as well as high quantum efficiencies. To avoid creating a leakage current during ball-bonding to the 1D array diodes, a ZnS layer was deposited on top of the CdTe passivation layer, as well as extra electroplated Au on the bonding pads. The median measured noise equivalent temperature difference (NETD) on a LWIR array was 14 mK for the 42 operable diodes. 2D arrays showed reasonably good uniformity of R0A and zero-bias current (I0) values. The first 64×64 element 2D array of 16×16 μm2 MWIR diodes has been hybridized to read-out electronics and gave median NETD of 60 mK. Images from both a 1D and a 2D array are shown.
10 citations
05 May 2006
TL;DR: In this article, the authors proposed a method for growing epitaxial MCT on a suitable substrate, which is then diced and hybridized on to the readout integrated circuit (ROIC).
Abstract: The standard process for manufacturing mercury cadmium telluride (MCT) infrared focal plane arrays (FPAs) involves hybridising detectors onto a readout integrated circuit (ROIC). Wafer scale processing is used to fabricate both the detector arrays and the ROICs. The detectors are usually made by growing epitaxial MCT on to a suitable substrate, which is then diced and hybridised on to the ROIC. It is this hybridisation process that prevents true wafer scale production; if the MCT could be grown directly onto the ROIC, then wafer scale production of infrared FPAs could be achieved. In order to achieve this, a ROIC compatible with the growth process needs to be designed and fabricated and the growth and processing procedures modified to ensure survival of the ROIC. Medium waveband IR detector test structures have been fabricated with resistance area product of around 3x10 4 Ω cm 2 at 77K. This is background limited in f/2 and demonstrates that wafer scale production is achievable.
9 citations
28 Sep 2006
TL;DR: The first generation of high performance thermal imaging sensors in the UK was based on two axis opto-mechanical scanning systems and small (4-16 element) arrays of the SPRITE detector, developed during the 1970s as mentioned in this paper.
Abstract: The first generation of high performance thermal imaging sensors in the UK was based on two axis opto-mechanical scanning systems and small (4-16 element) arrays of the SPRITE detector, developed during the 1970s. Almost two decades later, a 2nd Generation system, STAIRS C was introduced, based on single axis scanning and a long linear array of approximately 3000 elements. This paper addresses the development of the UK's 3rd Generation High Performance Thermal Imaging sensor systems, under a programme known as "Albion". Three new high performance detectors, manufactured in cadmium mercury telluride, operating in both MWIR and LWIR, providing high resolution and sensitivities without need for opto-mechanical scanning systems will be described. The CMT material is grown by MOVPE on low cost substrates and bump bonded to the silicon read out circuit (ROIC). All three detectors are designed to fit with existing standard Integrated Detector Cooling Assemblies (IDCAs). The two largest detectors will be integrated with field demonstrator cameras providing MWIR and LWIR solutions that can rapidly be tailored to specific military requirements. The remaining detector will be a LWIR device with a smart ROIC, facilitating integration times much longer than can typically be achieved with focal plane arrays and consequently yield very high thermal sensitivity. This device will be demonstrated in a lab based camera system.
9 citations
07 Mar 2006
TL;DR: In this article, recursive triangulation using a bearings-only sensor is investigated for a fly-by scenario, and several estimators are compared, fundamental estimation limits are calculated for different measurement noise assumptions.
Abstract: Recursive triangulation, using a bearings-only sensor, is investigated for a fly-by scenario. In a simulation study, several estimators are compared, fundamental estimation limits are calculated for different measurement noise assumptions. The quality of the estimated state distributions is evaluated.
8 citations