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Gunapala, S. D.

Publications and source records attributed to Gunapala, S. D..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Quantum Well Infrared Photodetectors for low background application

QWIPs operate by photoexcitation of electrons between ground and first excited state subbands of multi-quantum wells (MQWs) which are artificially fabricated by placing thin layers of two dfferent, high-bandgap semiconductor materials alternately. The bandgap discontinuity of two materials creates quantized subbands in the potential wells associated with conduction bands.

infrared focal plane arrays quantum wells↗
NASA NTRS2000

Recent Developments and Applications of Quantum Well Infrared Photodetector Focal Plane Arrays

There are many applications that require long wavelength, large, uniform, reproducible, low cost, stable, and radiation-hard infrared (IR) focal plane arrays (FPAs). For example, the absorption lines of many gas molecules, such as ozone, water, carbon monoxide, carbon dioxide, and nitrous oxide occur in the wavelength region from 3 to 18 micron. Thus, IR imaging systems that operate in the long wavelength IR (LWIR) region (6 - 18 micron) are required in many space borne applications such as monitoring the global atmospheric temperature profiles, relative humidity profiles, cloud characteristics, and the distribution of minor constituents in the atmosphere which are being planned for future NASA Earth and planetary remote sensing systems. Due to higher radiation hardness, lower 1/f noise, and larger array size the GaAs based Quantum Well Infrared Photodetector (QWIP) FPAs are very attractive for such space borne applications compared to intrinsic narrow band gap detector arrays. In this presentation we will discuss the optimization of the detector design, material growth and processing that has culminated in realization of large format long-wavelength QWIP FPAs, portable and miniature LWIR cameras, holding forth great promise for myriad applications in 6-18 micron wavelength range in science, medicine, defense and industry. In addition, we will present some system demonstrations using broadband, two-color, and high quantum efficiency long-wavelength QWIP FPAs.

Gunapala, S. D.↗
NASA NTRS2000

8-9 and 14-15 Micron Two-Color 640x486 GaAs/AlGaAs Quantum Well Infrared Photodetector (QWIP) Focal Plane Array Camera

An optimized long-wavelength two-color Quantum Well Infrared Photodetector (QWIP) device structure has been designed. This device structure was grown on a three inch semi-insulating GaAs substrate by molecular beam epitaxy (MBE). This wafer was processed into several 640x486 format monolithically integrated 8-9 and 14-15 micron two color (or dual wavelength) QWIP focal plane arrays (FPAs). These FPAs were then hybridized to 640x486 silicon CMOS readout multiplexers. A thinned (i.e., substrate removed) FPA hybrid was integrated into a liquid helium cooled dewar to perform electrical and optical characterization and to demonstrate simultaneous two-color imagery. The 8-9 micron detectors in the FPA have shown background limited performance (BLIP) at 70 K operating temperature, at 300 K background with f/2 cold stop. The 14-15 micron detectors of the FPA have reached BLIP at 40 K operating temperature at the same background conditions. In this presentation we discuss the performance of this long-wavelength dualband QWIP FPA in quantum efficiency, detectivity, noise equivalent temperature difference (NEAT), uniformity, and operability.

Gunapala, S. D.↗
NASA NTRS1999

Recent developments and applications of Quantum Well Infrared Photodetector focal plane arrays

In this paper we discuss the optimization of the detector design, material growth and processing that has culminated in realization of 15 micron cutoff 128x128 QWIP focal plane array camera, hand-held and palmsize 256x256 long wavelength QWIP cameras and 648x480 long-wavelength camera, holding forth great promise for myriad applications in 6-25 micron wavelength range in science, medicine, defense and industry.

multi-quantum-wells↗
NASA NTRS1998

Bandgap Shifting of an Ultra-Thin InGaAs/InP Quantum Well Infrared Photodetector

We demonstrate that SiO(sub 2) cap annealing in the ultra-thin p-type InGaAs/InP quantum wells can be used to produce large blue shifts of the band edge. A substantial bandgap blue shift, as much a 292.5 meV at 900 degrees C have been measured and the value of the bandgap shift can be controlled by the anneal time.

Bandgap shifting photodetector quantum well infrar↗
NASA NTRS1998

Recent Progress in Quantum Well Infrared Photodetector Research and Development at Jet Propulsion Laboratory

One of the simplest device realizations of the classic particle-in-the-box problem of basic quantum mechanics is the Quantum Well Infrared Photodetector (QWIP). In this paper we discuss the optimization of the detector design, material growth and processing that has culminated in realization of 15 micron cutoff 128x128 QWIP focal plane array camera, hand-held and palmsize 256x256 long-wavelength QWIP cameras and 648x480 long-wavelength cameras, holding forth great promise for myriad applications in 6-25 micron wavelength range in science, medicine, defense and industry.

quantum↗
NASA NTRS1998

Wavelength Shifting in InP based Ultra-thin Quantum Well Infrared Photodetectors

We have demonstrated red-shifting of the wavelength response of a bound-to-continuum p-type ultra-thin InGaAs/Inp quantum well infrared photodetector after growth via rapid thermal annealing. Compared to the as-grown detector, the peak spectral response of the annealed detector was shifted to longer wavelength without any major degradation in responsivity characteristics.

Photodetector Thermal Annealing↗
NASA NTRS1998

Quantum Well Infrared Photodetectors for Low Background Applications

High performance long-wavelength GaAs/Al(x)Ga(1-x)As quantum well infrared photodetectors for low background applications have been demonstrated. This is the first theoretical analysis of quantum well infrared photodetectors for low background applications and the detectivity D* of 6 x 10(exp 13) cm.square root of Hz/W has been achieved at T = 40 K with 2 x 10(exp 9) photons/cm2/sec background. In addition, this paper describes the demonstration of mid-wavelength/long-wavelength dualband quantum well infrared photodetectors and long-wavelength/very long-wavelength dualband quantum well infrared photodetectors in 4-26 micrometers wavelength region.

Gunapala, S. D.↗
NASA NTRS1998

Quantum Well Infrared Photodetectors (QWIPs) for Astronomy

In recent years, many research groups in the world have demonstrated large format Quantum Well Infrared Photodetector (QWIP) focal plane arrays for various thermal imaging applications. QWIPs as opposed to conventional low bandgap infrared detectors, are limited by thermionic dark current and not tunneling currents down to 30K or less. As a result the performance of QWIPs can be substantially improved (orders of magnitude) by cooling from 70K to 30K. Cooling does not induce any nonuniformity or 1/f noise in QWIP focal plane arrays. In this paper, we discuss the development of highly uniform long- wavelength QWIPs for astronomical applications.

Gunapala, S. D.↗