Gabby Sarusi

Improved performance of quantum well infrared photodetectors using random scattering optical coupling

We demonstrate that a random scattering reflector on top of a quantum well infrared photodetector increases the optical coupling (i.e., increases the infrared absorption, responsivity, and detectivity) by an order of magnitude compared with a one‐dimensional grating or 45° angle of incidence geometry.

OPTIMIZATION OF TWO DIMENSIONAL GRATINGS FOR VERY LONG WAVELENGTH QUANTUM WELL INFRARED PHOTODETECTORS

We have performed a detailed study of two‐dimensional grating coupling for quantum well infrared photodetectors in the very long wavelength spectral region λ∼16–17 μm. Using calculations based on the modal expansion method we quantitatively explain the double peaked responsivity spectrum. By optimizing the grating parameters we achieve a normal incidence responsivity and detectivity which are three times larger than the 45° angle of incidence geometry.

Very long wavelength InxGa1−xAs/GaAs quantum well infrared photodetectors

We demonstrate a long wavelength (λc=20 μm) quantum well infrared photodetector using nonlattice matched InxGa1−xAs/GaAs materials system. High optical gains (low capture probabilities) were achieved by using GaAs as a barrier material in this system. A detectivity of D*=9.7×1010 cm√Hz/W at T=10 K has been achieved.

Design and performance of very long‐wavelength GaAs/AlxGa1−xAs quantum‐well infrared photodetectors

We present an extensive and detailed study of very long wavelength quantum well infrared photodetectors covering the spectral region between 14 and 20 μm. Measurements were made on seven different molecular beam epitaxy grown samples having different well widths and barrier heights. In this study we combine experimental results with theoretical analysis and focus on the relationship between the quantum well structure and detector performance, i.e., responsivity, dark current, dynamic resistance, noise current, optical‐gain, and detectivity. These results provide the basis for further optimization, and the detector parameters needed for the design of the readout circuit for focal plane arrays.

1 Gb/s Si high quantum efficiency monolithically integrable λ=0.88 μm detector

We propose and demonstrate a 1 Gb/s high quantum efficiency Si MSM metal‐semiconductor‐metal detector which is complementary metal‐oxide semiconductor compatible. The detector absorbs over 50% of the light entering the active layer at a wavelength of λ=0.88 μm.

High Performance InGaAs/GaAs Quantum Well Infrared Photodetectors

We have measured the optical and transport properties of In0.2Ga0.8As/GaAs quantum well infrared photodetectors based on bound‐to‐bound, bound‐to‐quasibound, and bound‐to‐continuum intersubband transitions. Excellent hot electron transport and high detectivity D*=1.8×1010 cm√Hz/W (at λp=16.7 μm) were achieved at temperature T=40 K.

QWIP or other alternative for third generation infrared systems

Abstract Choosing the right detector technology for third generation thermal imaging systems is directly derived from the requirements of these new generation infrared imaging systems. It is now evident that third generation thermal imager will still need the higher resolution capabilities as well as capabilities in multispectral detection and polarization sensitivity. Four technologies candidates are analyzed; the field-proved HgCdTe (MCT), uncooled microbolometer technology, antimonide based materials and quantum well infrared photodetectors (QWIP). Taking into account the risks, maturity and technologies barrier of each technology, we claim that for non-strategic applications (not low background conditions), QWIP technology is the most favorite. The ternary and superlattice antimonide based materials group seems to be theoretically the best alternative, but are not recommended due to its immaturity and the high risk involved in this technology (passivation, doping control, etc.). We anticipate large penetration of the uncooled detectors to the low-end and medium-end market. The HgCdTe will still be in progress due to the inertia of the large funding and the strategic importance of this detectors technology.

Chemically deposited PbS thin film photo-conducting layers for optically addressed spatial light modulators

Lead sulfide semiconducting thin films were chemically deposited on indium tin oxide coated glass plates for use as photoreceptor layers in conjugation with optically addressed spatial light modulators (OASLMs). Deposition conditions such as temperature, reagent concentration, pH and deposition time were optimized in order to achieve homogeneous, continuous and adherent films. Mirror-like films with tunable particle size and film thickness were obtained. The microstructure and morphology evolution of the films were investigated using X-ray diffraction, scanning electron microscopy and atomic force microscopy. Electrical and optical properties were studied using four-point probe measurements, FTIR spectroscopy, photoluminescence spectroscopy, photo-current and photo-voltage measurements. Blue shift of the band gap to the short wavelength infra-red (SWIR) range was obtained as a function of particle size, and significant photovoltaic effect was measured. The resistivity of the films, as well as their photo-voltage response, were enhanced after thermal annealing. These results indicate that PbS films can serve as effective photoreceptors in OASLMs for applications including SWIR detection for night vision purposes.

Enhanced SWIR absorption in chemical bath deposited PbS thin films alloyed with thorium and oxygen

We report on chemically deposited thin films of PbS alloyed with thorium. Control over the thorium content in the films was achieved by lowering the solution pH and compensating by adding tri sodium citrate as a co-complexant. Homogeneous distribution of thorium was achieved, accompanied by substantial oxygen content, up to concentrations of 9 at% thorium and 20 at% oxygen. Regardless of these relatively high concentrations, a single phase of alloyed PbS was found in X-ray and electron diffraction, indicating complete solubility of the species within the lattice. Physical properties such as the optical band gap and transmission spectra showed a strong dependence on thorium content due to chemical variations and size dependent quantum confinement. This new system is a promising candidate for electro-optic applications due to ease of band-gap tuning and enhanced optical absorption in the short wave infrared (SWIR) range.

A monolithic LWIR/NIR multispectral QWIP for night vision and see spot

A two stack two color quantum well infrared photodetector (QWIP) for simultaneously detection of LWIR and near infrared (NIR) radiation is demonstrated. The LWIR sensor is based on a regular GaAs/AlGaAs QWIP, while the NIR sensor is based on a strained InGaAs/GaAs quantum wells structure. Optical and electrical measurements of the NIR detector and the inclusive device are presented and discussed.