Project Title:

Long-Wavelength, Gated, Mercury-Cadmium-Telluride, N+N-P, Photodiodes for Heterodyne

08.12-6000
912004
Long-Wavelength, Gated, Mercury-Cadmium-Telluride, N+N-P, Photodiodes for Heterodyne
Applications
Spire Corporation
One Patriots Park
Bedford
MA
01730-2396
Nasser H.
Karam
617-275-6000
GSFC
NAS5-31930
156

08.12-6000
912004

Abstract:

Long-Wavelength, Gated, Mercury-Cadmium-Telluride, N+N-P, Photodiodes for Heterodyne
Applications
High-sensitivity, wide bandwidth, photomixers operating at 15 to 30 microns are of
great interest for applications that range from the detection of molecular species,
both within the atmosphere and in outer space, to the determination of wind velocities
and distribution from satellite-based systems. HgCdTe photodiodes are the detector
of choice because of their tunable band gap. Previous investigations in this area
concluded that better surface passivation and material quality were required to improve
device performance. By applying state-of-the-art CdTe passivation to a gated N+N-P
detector structure on MOCVD HgCdTe, control of the surface leakage currents that
can degrade device performance will be achieved. Phase I will demonstrate the photodetector
structure on CdTe substrates and will determine its heterodyne sensitivity by analysis
of variable temperature data. Phase II will apply the same structure to HgCdTe grown
on GaAs and/or GaAs on Si substrates by MOCVD. Selective area epitaxy will be utilized
for the fabrication of monolithic HgCdTe photomixers and preamplifiers for faster,
more compact, lighter detectors with superior performance and radiation resistance.
Improved and more producible long wavelength photomixers will find their way into
a variety of instruments in which heterodyne radiometry is applied. These will include
infrared spectrometers, gas analyzers for field use, and LIDAR systems for the detection
of localized atmospheric disturbances (such as wind shear).
heterodyne, HgCdTe, CdTe, GaAs, MOCVD, photodiodes, preamplifiers