Bob Grietens

1.7–1.9 μm InxGa1−xAs/InyAl1−yAs light‐emitting diodes lattice‐mismatched grown on GaAs

InxGa1−xAs/InyAl1−yAs based light‐emitting diodes emitting in the wavelength range 1.7–1.9 μm have been grown nonlattice matched on GaAs. Electroluminescence spectra are measured at 77 K and the injection level dependence has been studied. Mechanisms that broaden the lineshape are discussed. The position of the band gap and the electron temperature are derived by fitting the spectra. Band gap narrowing was observed as a function of the injected carrier density.

Compositional dependence of AlAsySb1−y ternaries on the ratio of Sb/As fluxes and on the substrate temperature

We present a systematic study of the compositional dependence of AlAsySb1−y layers, grown by molecular beam epitaxy, on the ratio of As to Sb fluxes and on the substrate temperature. The initial results clearly demonstrate that variations in the composition can be observed by changing the above‐mentioned parameters. The emphasis of this communication is on understanding the qualitative trends of these dependencies.

Molecular Beam Epitaxial Growth of Bulk AlAs0.16Sb0.84 and AlAs0.16Sb0.84/InAs Superlattices on Lattice-Matched InAs Substrates

AlAs0.16Sb0.84 ternaries and AlAs0.16Sb0.84/InAs superlattices have been grown by molecular beam epitaxy lattice-matched on InAs substrates. The compositional dependence of AlAsy Sb1-y on the ratio of Sb4 to As2 fluxes as well as on the substrate temperature has been investigated and can be explained qualitatively. The growth of AlAs0.16Sb0.84/InAs superlattices is described and illustrated by the results of reflection high-energy electron diffraction measurements. The crystalline quality of the superlattices is demonstrated by means of transmission electron microscopy and X-ray diffraction measurements.

Micromachined poly-SiGe bolometer arrays for infrared imaging and spectroscopy

The state-of-the-art characteristics of micromachined polycrystalline SiGe microbolometer arrays are reported. An average NETD of 85 mK at a time constant of 14 ms is already achievable on typical self-supported 50 μm pixels in a linear 64-element array. In order to reach these values, the design optimization was performed based on the performance characteristics of linear 32-, 64- and 128-element arrays of 50-, 60- and 75-μm-pixel bolometers on several detector lots. The infrared and thermal modeling accounting for the read-out properties and self-heating effect in bolometers resulted in improved designs and competitive NETD values of 80 mK on 50 μm pixels in a 160x128 format at standard frame rates and f-number of 1. In parallel, the TCR-to-1/f noise ratio and the mechanical design of the pixels were improved making poly-SiGe a good candidate for a low-cost uncooled thermal array. The technological CMOS-based process possesses an attractive balance between characteristics and price, and allows the micromachining of thin structures, less than 0.2 μm. The resistance and TCR non-uniformity with σ/μ better than 0.2% combined with 99.93% yield are demonstrated. The first lots of fully processed linear arrays have already come from the IMEC process line and the results of characterization are presented. Next year, the first linear and small 2D arrays will be introduced on the market.

InAs/(GaIn)Sb superlattices for IR optoelectronics: Strain optimization by controlled interface formation

Abstract The structural properties of InAs/(GaIn)Sb and (InGa)As/GaSb superlattices (SLs), grown by solid-source molecular-beam epitaxy on (0 0 1) GaAs substrates using a strain relaxed GaSb or InAs buffer layer or directly on (0 0 1) InAs substrates, were analyzed by high-resolution X-ray diffraction and Raman spectroscopy. The residual strain within the SL was found to depend critically on the type of interface bonds, which can be either InSb- or GaAs-like. Thus, to achieve lattice matching to the buffer layer or substrate by strain compensation within the SL stack, the controlled formation of the interface bonds is vital. On the other hand, minimization of the residual strain is shown to be a prerequisite for achieving a high photoluminescence yield and high responsivities for InAs/(GaIn)Sb SL based IR detectors.

Optimization of design and technology for uncooled poly-SiGe microbolometer arrays

The performance characteristics of polycrystalline SiGe microbolometer arrays are the subject of both design and technological optimizations performed in this work to move the arrays towards the production. An NETD of 90 mK at a time constant of 11 ms is already achievable for the best non-optimized 60 micrometers pixel, 0.26 micrometers thick bolometer design in a linear 128 pixel array according to the results of LWIR characterization. The performance of linear 32, 64 and 128 element arrays of 50-, 60- and 75-micrometers pixel bolometers made with 0.26...0.13 micrometers thin poly-SiGe on several wafer runs was the starting point for the computer simulation of detector features and evolution of its characteristics under reading bias pulses. The material properties and parameters of read-outs are taken into account in the optimization of the design parameters of arrays as well. The typical bolometer characteristics achieved on the latest wafer run if processed with the PC-program accounting for the read-out and heating effects, result in an average NETD of 70 mK at a time constant of 17 ms for 50 micrometers pixels in a 320x240 array. Despite less TCR-to-1/f noise ratio as compared with VOx arrays, the several advantages make poly-SiGe a very attractive candidate for an uncooled array, i.e. full compatibility with CMOS technology, better characteristics/price ratio, resistance nonuniformity s/mean <0.2%, and a possibility to release extra-thin structures.

3000 pixel linear InGaAs sensor for the Proba-V satellite

We report on the design and development of the large linear SWIR focal plane arrays to be deployed in the multispectral instrument of the Proba-V satellite. These sensors are based on mechanical butting of three InGaAs photodiode arrays with 1024 pixels on 25 μm pitch, forming a nearly continuous line of 3072 pixels. A new read-out integrated circuit (ROIC) for photocurrent integration and signal multiplexing with 1024 inputs was designed and manufactured by stitching due to the length of the chip. The ROIC (XRO3508) includes both correlated double sampling (CDS) and autozero features, enabling a very low Dark Signal Non Uniformity (DSNU) and Photoresponse Non-Uniformity (PRNU) less than 0.5% of the available signal range.

Cheetah: A high frame rate, high resolution SWIR image camera

A high resolution, high frame rate InGaAs based image sensor and associated camera has been developed. The sensor and the camera are capable of recording and delivering more than 1700 full 640x512pixel frames per second. The FPA utilizes a low lag CTIA current integrator in each pixel, enabling integration times shorter than one microsecond. On-chip logics allows for four different sub windows to be read out simultaneously at even higher rates. The spectral sensitivity of the FPA is situated in the SWIR range [0.9-1.7 µm] and can be further extended into the Visible and NIR range. The Cheetah camera has max 16 GB of on-board memory to store the acquired images and transfer the data over a Gigabit Ethernet connection to the PC. The camera is also equipped with a full CameralinkTM interface to directly stream the data to a frame grabber or dedicated image processing unit. The Cheetah camera is completely under software control.

Thermal infrared detection using linear arrays of poly SiGe uncooled microbolometers

In this paper, we discuss the SiGe technology for uncooled microbolometer arrays of small format, ie 200/spl times/1 and 14/spl times/14, is transferred from IMEC to XenICs allowing of the poly-SiGe arrays for application in non-contact temperature measurements, infrared spectroscopy, technological process monitoring, quality control, etc. The arrays demonstrate an exceptional uniformity, about 100% pixel yield, 100% operability, and a NETD of about 100 mK at a readout level. These advantages combined with a possibility of hermetic zero-level micropacking make the SiGe technology a proper one for the low-cost production of infrared arrays.

Growth and characterization of mid‐infrared InGaAs/InAlAs strained triple‐quantum‐well light‐emitting diodes grown on lattice‐mismatched GaAs substrates

Strained triple‐quantum‐well In0.9Ga0.1As/In0.8Al0.2As light‐emitting diodes were grown on lattice‐mismatched GaAs substrates by molecular‐beam epitaxy. The diodes exhibit room‐temperature external electroluminescent light emission at 2.4 μm with efficiencies up to 6.4×10−5. The maximum output power at room temperature is 1.85 μW under pulsed operation at 150 mA, (1 kHz, 50% duty cycle). Although the diodes have excellent electrical properties, their optical performance is still found to be limited by the nonradiative Shockley–Read–Hall recombination.