US Government As Represented by the Secretary of the Army

Other

Michael Wraback

Paul H Shen

Anand Venktesh Sampath

Charles J Collins

Mitra Dutta

Gregory Alan Garrett

Grace D Metcalfe

H Paul Shen

Yicheng Lu

Xin Zhang

Jagadeesh Pamulapati

Richard Douglas Averitt

Chandrasekhar R Gorla

Meredith Reed

Kebin Fan

Shaohua Liang

Andrew Strikwerda

Lee Ellen Rodak

Chad Stephen Gallinat

Vijay S Parameshwaran

Paul Hongen Shen

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 reflection-mode waveplate for operation in the terahertz region by shifting the phase between two perpendicular polarization components of the light wave, comprising a ground plane; an array of polygonal unit cells; the polygonal unit cells comprising a polymer positioned between the ground plane and the exterior of the array of polygonal patches.

Electromagnetic composite-based reflecting terahertz waveplate

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 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.

Ultraviolet light emitting AlGaN composition and ultraviolet light emitting device containing same

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

Ultraviolet light emitting AlGaN composition, and ultraviolet light emitting device containing same

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

Methods and devices for creating an anisotropic strain in a semiconductor quantum well structure to induce anisotropy thereof are disclosed herein. Initially, a substrate is provided, and a quantum well structure formed upon the substrate. A first crystalline layer (e.g., a GaAs layer) having a first crystalline phase can then be deposited upon the quantum well structure. Thereafter, a second crystalline layer (e.g., a GaN layer) having a second crystalline phase and a thickness thereof can be formed upon the first crystalline layer to thereby induce an anisotropic strain in the quantum well structure to produce a quantum well device thereof. Additionally, the second crystalline layer (e.g., GaN) can be formed from a transparent material and utilized as an anti-reflection layer. By properly choosing the thickness of the second crystalline layer (e.g., a GaN layer), a desired anisotropic strain as well as a desired anti-reflection wavelength can be achieved.

Creation of anisotropic strain in semiconductor quantum well

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.

Growing community of inventors

Germantown, MD, United States of America

Michael Wraback