Sandip K. Sengupta

Schottky diodes using poly(3‐hexylthiophene)

Schottky barrier diodes have been fabricated using poly(3‐hexylthiophene)(P3HT) as the semiconductor and indium as the metal. P3HT was doped with FeCl3 at room temperature to form a p‐type semiconductor. The Schottky junctions of In on FeCl3‐doped P3HT using pressure contact exhibit rectification ratios ranging from 104:1 to 106:1 at a bias of ±1 V.

Photoconductive optically driven deformable membrane for spatial light modulator applications utilizing GaAs substrates.

The fabrication and characterization of an optically addressable deformable mirror for a spatial light modulator is described. Device operation utilizes an electrostatically driven pixellated aluminized polymeric membrane mirror supported above an optically controlled photoconductive GaAs substrate. A 5 microm thick grid of patterned photoresist supports the 2 microm thick aluminized Mylar membrane. A conductive ZnO layer is placed on the back side of the GaAs wafer. A standard Michelson interferometer is used to measure mirror deformation data as a function of illumination, applied voltage, and frequency. A simplified analysis of device operation is also presented.

Temperature and electric-field dependences of hole mobility in light-emitting diodes based on poly [2-methoxy-5-(2-ethylhexoxy)-1,4-phenylene vinylene]

The current-voltage characteristics of poly [2-methoxy-5-(2-ethylhexoxy)-1,4-phenylene vinylene] (MEH-PPV)-based hole-only light-emitting diodes are measured as a function of temperature. The hole current is found to be space-charge limited, providing a direct measure of the mobility as a function of temperature and electric field. A thermal activation energy of 0.2eV is obtained for the zero-field mobility, with a room-temperature low-field mobility value for holes of 3.3×10−7cm2∕Vs. The hole mobility exhibits field dependence in accordance with the Poole-Frenkel effect. The combination of space-charge effects and field-dependent mobility thus provides a consistent description of hole transport as a function of temperature and bias voltage in MEH-PPV films.

Schottky diodes of poly(3-undecylthiophene) containing fullerene C60

Abstract The conducting polymer poly(3-undecylthiophene) (PUT) was doped with fullerene C60. The effects of doping on the current-voltage characteristics of aluminum Schottky contacts in the dark and under 488 nm laser illumination were investigated. C60 doping produced near ideal Schottky behavior, changed the optical absorption and introduced an acceptor level.

Schottky and Metal-Insulator-Semiconductor Diodes Using Poly(3-hexylthiophene)

The semiconducting polymer poly(3-hexylthiophene) (P3HT) has been previously used to fabricate Schottky barriers and metal-insulator-semiconductor (MIS) tunnel diodes using indium as the blocking contact. When P3HT is doped with FeCl3, the conductivity increases and the polymer behaves as a p-type semiconductor. Schottky junctions fabricated on the doped material exhibited higher rectification ratios than equivalent junctions fabricated on undoped material. An indium contact evaporated on FeCl3-doped P3HT film gave the current-voltage ( I-V) characteristics of a minority carrier tunnel diode. Similar I-V characteristics were observed when a thin insulating polymer film was placed between the indium contact and the doped P3HT film.

Optically driven microelectromechanical-system deformable mirror under high-frequency AC bias

A new, optically addressed deformable mirror device is demonstrated. The device consists of a pixellated metalized polymeric membrane mirror supported above an optically addressed photoconductive substrate. A conductive transparent ZnO layer is deposited on the back side of the substrate. A very high-frequency AC bias is applied between the membrane and the back electrode of the device. The membrane is deformed when the back of the device is illuminated because of impedance and bias redistribution between two cascaded impedances. We fabricated, demonstrated, and modeled the operation of this device.

Patterned Multipixel Membrane Mirror MEMS Optically Addressed Spatial Light Modulator With Megahertz Response

In this letter, we report the fabrication, modeling and characterization of an all-optically addressed spring patterned silicon-nitride deformable mirror microelectromechanical-systems device. Combinations of high-frequency ac and dc bias voltages are applied across the device. The experimental verified theoretical modeling for this device shows the mirror deflection saturation as a function of light intensity appropriate for the dynamic range compression deconvolution. Frequency response up to 10MHz, practical for correcting very fast turbulences, was measured

Nonlinear dynamic range compression deconvolution.

We introduce a dynamic range image compression technique for nonlinear deconvolution; the impulse response of the distortion function and the noisy distorted image are jointly transformed to pump a clean reference beam in a two-beam coupling arrangement. The Fourier transform of the pumped reference beam contains the deconvolved image and its conjugate. In contrast to standard deconvolution approaches, for which noise can be a limiting factor in the performance, this approach allows the retrieval of distorted signals embedded in a very high-noise environment.

Mapping approach for image correction and processing for bidirectional resonant scanners

We have developed a mapping algorithm for correcting sinusoidally scanned images from their distortions. Our algorithm is based on the close relationship between linear and sinusoidal scanning. Straightforward implementation of this algorithm showed that the mapped image has either missing lines or redundant lines. The missing lines were filled by fusing the mapped image with its median-filtered or interpolated version. The implementation of this algorithm shows that it is possible to retrieve up to 98% of the original image (depending on the algorithm used for data fusion) as measured by the recovered energy. Excellent correction was obtained for both simulated scanned images and actual images from a scanning laser radar system.

Intelligent Systems Based on Ordered Arrays of Biological Molecules Using the LB Technique

The Langmuir-Blodgett (LB) technique has been used to incorporate photodynamic proteins into molecular assemblies. One technique of incorporation involves a generalized cassette attachment methodology which employs a biotin-streptavidin complexation with an electroactive polymer matrix. We have focused the efforts described here on phycobiliproteins and bacteriorho dopsin, although antibodies, enzymes, gene probes and other moieties could also be coupled into the system to build in selectivity. Photoconductivity and photobleaching of these protein systems were investigated. These results suggest that coupling these proteins, either in mixed monolayers or in multilayers, with appropriate conductive polymers or other materials will provide the opto electronic signal transduction needed for biosensor, optical display and other applications. Initial studies involving the integration of conductive polymers into the molecular assemblies to enhance optical signal transduction are also discussed.