US Government As Represented by the Secretary of the Army

Other

Paul H Shen

Michael Wraback

Mitra Dutta

Jagadeesh Pamulapati

Anand Venktesh Sampath

Weimin Zhou

Yicheng Lu

Barry Lee Stann

William Charles Ruff

Arthur D Ballato

Charles J Collins

Brian C Redman

Gerald J Iafrate

Michael A Stroscio

Chandrasekhar R Gorla

Richard H Wittstruck

Meredith Reed

Gregory Alan Garrett

Paul W Cooke

Shaohua Liang

Grace D Metcalfe

Lee Ellen Rodak

Chad Stephen Gallinat

Vijay S Parameshwaran

Wayne H Chang

Keith M Aliberti

Disclosed is a semiconductor-liquid junction based photoelectrochemical (PEC) cell for the unassisted solar splitting of water into hydrogen and oxygen gas, the solar-driven reduction of COto higher-order hydrocarbons, and the solar-driven synthesis of NH. The disclosed system can employ a photocathode based upon wurtzite hexagonal semiconductors that can be tailored with proper band alignment for the redox potentials for water, COreduction, and NHproduction, and with bandgap energy for maximum solar absorption. The design maximizes the carrier collection efficiency by leveraging spontaneous and piezoelectric polarization in these materials systems to generate hot electrons within the photocathode. These electrons have sufficient excess energy, preserved at a designed energy capture region, to overcome the kinetic overpotential (surface chemistry limitation) required for the reactions to occur at a high rate.

Electron acceleration and capture device for preserving excess kinetic energy to drive electrochemical reduction reactions

A photodiode for detecting photons comprising a substrate; first semiconducting region suitable for forming a contact thereon; a first contact; a second semiconducting region comprising an absorption region for the photons and being formed of a semiconductor having one or more of a high surface recombination velocity or a high interface recombination velocity; a second contact operatively associated with the second region; the first semiconducting region and the second semiconducting region forming a first interface; the second semiconducting region being configured such that reverse biasing the photodiode between the first and second contacts results in the absorption region having a portion depleted of electrical carriers and an undepleted portion at the reverse bias point of operation; the undepleted portion being smaller than the absorption depth for photons; whereby the depletion results in the creation of an electric field and photogenerated carriers are collected by drift; and a method of making.

Enhanced deep ultraviolet photodetector and method thereof

A method of making and a photodetector comprising a substrate; a p-type or n-type layer; first and second region each having polarizations, a first interface therebetween, the magnitudes and directions of the first and second polarizations being such that a scalar projection of second polarization on the growth direction relative to the scalar projection of the first polarization projected onto the growth direction is sufficient to create a first interface charge; and a third region suitable for forming one of an n-metal or p-metal contact thereon having a third polarization, a second interface between the second and third regions, the third polarization having a scalar projection on the growth direction that, relative to scalar projection of the second polarization onto the growth direction, is sufficient to create a second interface charge; the first and second interface charges creating an electrostatic potential barrier to carriers defining a predetermined wavelength range.

Variable range photodetector and method thereof

An avalanche photodetector comprising a multiplication layer formed of a first material having a first polarization; the multiplication layer having a first electric field upon application of a bias voltage; an absorption layer formed of a second material having a second polarization forming an interface with the multiplication layer; the absorption layer having a second electric field upon application of the bias voltage, the second electric field being less than the first electric field or substantially zero, carriers created by light absorbed in the absorption layer being multiplied in the multiplication layer due to the first electric field; the absorption layer having a second polarization which is greater or less than the first polarization to thereby create an interface charge; the interface charge being positive when the first material predominately multiplies holes, the interface charge being negative when the first material predominately multiplies electrons, the change in electric field at the interface occurring abruptly at the atomic level; the interface charge creating electric field discontinuity causing first electric field to attain the breakdown field in the multiplication region and the second electric field to be low or zero in the absorption layer to thereby eliminate the need for a doped charge layer and the associated thickness of the doped charge layer required to transition from the low field to the high field. Also claimed is a method of making.

Polarization enhanced avalanche photodetector and method thereof

A detection device comprising a photodetector comprising a first semiconductor layer through which light first enters the photodetector; the first semiconductor layer formed of a first semiconductor material crystal lattice which terminates at an interface creating a first interface charge; the first semiconductor layer being an absorption layer in which photons in a predetermined wavelength range are absorbed and create photogenerated carriers; and a second polar semiconductor layer deposited on the crystal lattice of the first semiconductor layer substantially transparent to light in the predetermined wavelength range and having a total polarization different from the first semiconductor layer so that a second interface charge is induced at the interface between the first and second semiconductor layers; the induced second interface charge reduces or substantially cancels the first interface charge so as to increase the collection of photogenerated carriers by the photodetector. ; and a methodproviding the above.

Semiconductor photodetector with transparent interface charge control layer and method thereof

A method and device for generating terahertz radiation comprising a substrate; a plurality of segments of polar crystal material formed on the substrate, the segments having an internal electric polarization; each segment comprising at least two edges oriented substantially perpendicular to the polar axis such that the electric polarization terminates at the edges and the segment comprises a majority of positive charges on one edge and a majority of negative charges on the opposite edge thereby leading to creation of an internal electric field; whereby when irradiated by a pulsed source of duration less than one picosecond, electron-hole pairs are generated within the segments and the internal electric field separates and accelerates the electron-hole pairs to thereby produce terahertz radiation.

Terahertz radiation device and method of generating terahertz radiation

A method and device for generating terahertz radiation comprising a plurality of layers of polar crystal material operative to emit terahertz radiation; the plurality of layers comprising transport layers and divider layers, the plane of the layers being not parallel to the polar axis, the interface between the transport layers and divider layers forming boundaries at which the internal electric polarization terminates leading to charges accumulating at the boundaries, and creation of internal electric fields oriented along the polar axis.

Terahertz radiation device using polar semiconductor materials and method of generating terahertz radiation

A light emitting device comprising: a polar template; a p-type layer grown thereon; the p-type layer having a first polarization vector having a first projection relative to a growth direction; an n-type layer grown on the p-type layer; the n-type layer having a second polarization vector that is larger than the first polarization vector; the n-type layer and p-type layer forming an interface. Another preferred embodiment light emitting device comprises a polar template; an n-type layer grown on the template; the n-type layer having a first polarization vector having a first projection relative to a growth direction; a p-type layer grown on the n-type layer having a second polarization vector that is larger than the first polarization vector. In both embodiments, the first polarization vector in the p-layer and second polarization vector in the n-layer create discontinuity at the interface resulting in a negative charge appearing at the interface.

Light emitting diode

A method and device for generating terahertz radiation comprising a polar crystal material layer operative to emit terahertz radiation; the polar crystal material layer comprising a plurality of stacking faults; the stacking faults lying substantially perpendicular to the polar axis and forming boundaries at which the internal electric polarization terminates leading to charges accumulating at the boundaries, and creation of internal electric fields oriented along the polar axis; a pulsed radiation source for creating photogenerated carriers in the polar crystal material; whereby the photogenerated carriers accelerate in the internal electric fields associated with the termination of the internal electric polarization by the stacking faults to thereby generate terahertz radiation.

Method and apparatus for enhanced terahertz radiation from high stacking fault density

An AlGaN composition is provided comprising a group III-Nitride active region layer, for use in an active region of a UV light emitting device, wherein light-generation occurs through radiative recombination of carriers in nanometer scale size, compositionally inhomogeneous regions having band-gap energy less than the surrounding material. Further, a semiconductor UV light emitting device having an active region layer comprised of the AlGaN composition above is provided, as well as a method of producing the AlGaN composition and semiconductor UV light emitting device, involving molecular beam epitaxy.

Method of manufacturing an ultraviolet light emitting AlGaN composition and ultraviolet light emitting device containing same

A system and method for performing high-resolution imagery of a target are provided. One embodiment is a method of performing high-resolution imagery of a target comprising: generating a chirped waveform that modulates a light signal transmitted toward a target for performing active LADAR of the target; generating a low-frequency local oscillator waveform for performing active imaging; and simultaneously performing passive imaging and active LADAR.

Systems and methods for performing active LADAR and passive high resolution imagery

A high range resolution ladar includes a chirp generator for producing a chirp signal waveform that is used by a laser diode to propagate a divergent laser light waveform. The reflected light signals from the target are directed to a self mixing detector that is coupled to the chirp generator where the responsivity of the detector varies in accordance with the chirp waveform for converting reflected light signals from the target to electrical signals and for mixing the converted electrical signal with the chirp waveform to produce an output electrical signal whose frequency is proportional to the range to the target. The self-mixing detector includes at least one detector having a semiconductor substrate and first and second electrodes deposited on the substrate and spaced from each other, wherein the first set of electrodes is connected to the chirp generator and the second set of electrodes is connected to a memory for storing a plurality of frames of image data.

Ladar system for detecting objects

A terahertz electromagnetic energy detector comprises a (100) oriented multiple quantum well thermally bonded to a first transparent substrate having a direction dependent thermal coefficient of expansion such that this coefficient matches the thermal coefficient of expansion of MQW in one direction but different form the direction-dependent thermal coefficient of expansion of the MQW in a perpendicular direction. The resultant internal thermally induced anisotropic strain leads to a polarization dependence of the optical absorption that is strongest near the lowest heavy-hole and light-hole exciton peaks. A second transparent substrate is placed beneath the first transparent substrate and is oriented so that its thermal coefficients of expansion act in a direction perpendicular to those of the first transparent substrate so that the accumulated phase retardation of the optical wave associated with birefringence of the substrate is effectively cancelled. A transverse electric and electromagnetic field is applied across the plane of the quantum well layers to ionize the excitons, which produces an anisotropic bleaching and concomitant line broadening of the anisotropic excitonic absorption. This phenomenon results in a polarization rotation of the transmitted optical field such that light passing through the device may be detected by a photosensitive polarization detector. The device is capable of effectively measuring the phase and frequency of terahertz energy over a wide bandwidth.

Method and apparatus for detection of terahertz electric fields using polarization-sensitive excitonic electroabsorption

A high contrast ultrahigh speed optically-addressed ultraviolet light modulator exploits the optical anisotropy in a ZnO film epitaxially grown on sapphire. This device, which could also be realized in a ZnO bulk crystal or similar wide bandgap material, achieves both high contrast and high speed by exploiting the anisotropic bleaching of the anisotropic absorption and concomitant ultrafast polarization rotation near the lowest exciton resonances produced by femtosecond ultraviolet pulses. The resultant modulation in a preferred embodiment is characterized by a contrast ratio of 70:1, corresponding to a dynamic polarization rotation of 12&deg;, and decays to a quasi-equilibrium value within 100 ps.

High contrast, ultrafast optically-addressed ultraviolet light modulator based upon optical anisotropy

An optical signal processor is implemented as a monolithically integrated semiconductor structure having optical waveguide devices forming beam splitters, optical amplifiers and optical phase shifters. The monolithic structure photonically controls a phased-array microwave antenna. Phase-locked master and slave lasers generate orthogonal light beams having a difference frequency that corresponds to the microwave carrier frequency of the phased-array antenna. The lasers feed the signal processor, which performs beam splitting, optical amplifying and phase shifting functions. A polarizer and an array of diode detectors convert optical output signals from the signal processor into microwave signals that feed the phased-array antenna. The optical waveguides of the signal processor are fabricated in a single selective epitaxial growth step on a semiconductor substrate.

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North Potomac, MD, United States of America

Paul H Shen