Michael A. Gritz

Development of device fabrication process for strained layer superlattice IR detectors

We report on progress in the development of a device fabrication process for type-II strained layer superlattice IR detectors, composed of InAs/GaSb or InAs/GaInSb. Steps of the process include etching the mesas, cleaning up the surface, and applying a surface passivation treatment. Certain etchants have been evaluated and calibrated. The surface has been studied with single wavelength ellipsometry and results have been compared with modeled ellipsometry values, revealing effects of surface residues and surface roughness. An initial investigation of ammonium sulfide treatment for surface passivation has been made. Initial measurements of the IR transmission of the GaSb substrate have also been made to determine how much thinning is needed for back side illuminated operation of the IR detectors.

Terahertz spectroscopy of TNT for explosive detection

Transmittance spectra of solid and vapor samples of trinitrotoluene (TNT) in the spectral range 0.6 to 10 THz at resolutions up to 1 GHz are reported. Uniform solid samples of ~100 &mgr;m thickness gave stronger absorption and more resolved structure than previous studies. New absorption lines for TNT solid below 100 cm-1 are reported. A heated 10 m multpass White cell was used for spectroscopy of the vapor. Strong absorption bands yield unexpectedly large absorption cross sections for the anticipated saturated vapor pressure at the cell temperature, leaving their assignment to TNT in doubt. These results indicate that path lengths exceeding 10 m and temperatures higher than 40 C, or significantly higher instrumental sensitivity, are needed for sensing of TNT vapor in the spectral range 0.6 to 10 THz.

Antenna Coupled Detectors for 2D Staring Focal Plane Arrays

Millimeter-wave (mmW)/sub-mmW/THz region of the electro-magnetic spectrum enables imaging thru clothing and other obscurants such as fog, clouds, smoke, sand, and dust. Therefore considerable interest exists in developing low cost millimeter-wave imaging (MMWI) systems. Previous MMWI systems have evolved from crude mechanically scanned, single element receiver systems into very complex multiple receiver camera systems. Initial systems required many expensive mmW integrated-circuit low-noise amplifiers. In order to reduce the cost and complexity of the existing systems, attempts have been made to develop new mmW imaging sensors employing direct detection arrays. In this paper, we report on Raytheon’s recent development of a unique focal plane array technology, which operates broadly from the mmW through the sub-mmW/THz region. Raytheon’s innovative nano-antenna based detector enables low cost production of 2D staring mmW focal plane arrays (mmW FPA), which not only have equivalent sensitivity and performance to existing MMWI systems, but require no mechanical scanning.

Direct detection antenna-coupled mmW sensors for the detection of explosive vapors

The low vapor pressure and concentration of explosive such as TNT and RDX pose significant problems for the detection of explosive vapors in the mmW bands. For the positive identification of explosive vapors using an uncooled passive mmW imaging spectrometer with a low false alarm rate (FAR) requires an unprecedented sensitivity of <150 fW. We report on the recent development of a novel uncooled mmW antenna-coupled direct detector, which shows promise of meeting this requirement.