US Government As Represented by the Secretary of the Army

Michael A Stroscio

Mitra Dutta

Gerald J Iafrate

Ki Wook Kim

Serge Luryi

Gregory L Belenky

Vladimir V Mitin

Rimvydas Mickevicius

Yuri M Sirenko

Mikhail Kisin

Arthur D Ballato

Paul H Shen

Hongen Shen

Viatcheslav Kochelap

Jun He

Harold L Grubin

Gerald J Lafrate

Intersubband semiconductor lasers (ISLs) are of great interest for mid-infrared (2-20 &#x3bc;m) device applications. These semiconductor devices have a wide range of applications from pollution detection and industrial monitoring to military functions. ISLs have generally encountered several problems which include slow intrawell intersubband relaxation times due to the large momentum transfer and small wave-function overlap of the initial and final electron states in interwell transitions. Overall, the ISL's of the prior art are subject to weak intersubband population inversion. The semiconductor device of the present invention provides optimal intersubband population inversion by providing a double quantum well active region in the semiconductor device. This region allows for small momentum transfer in the intersubband electron-phonon resonance with the substantial wave-function overlap characteristic of the intersubband scattering.

Intersubband semiconductor lasers with enhanced subband depopulation rate

A mesoscopic structure is fabricated such that the desired dominant modes of the acoustic phonons in the structure have wavelengths such that the length of a half-integral number of wavelengths equals the length of the structure through which the desired electron wave is propagating. A manner of achieving this object is to provide for a material in a quantum wire and a material at the end of the quantum wire such that the two materials have such different properties (as disclosed hereinafter) to abruptly dampen the phonon modes at the interface between the two materials. With such an interface, a clamped boundary condition will occur and the modes of amplitude can be assumed to vanish at the interface. Such a case applies at some metal-semiconductor interfaces. In particular, for a mesoscopic device having wire-like regions which terminate on a variety of metal regions (regions used as contacts, gates, barriers, etc.), it is satisfactory to apply clamped boundary conditions. At these boundaries, the acoustic modes will have nodes instead of the anti-nodes that are established in the case of an open boundary.

Mesoscopic electronic devices with tailored energy loss scattering

A carrier transport media is doped with impurities or includes barrier structures within or on the carrier transport media and a sinusoidally alternating external electric field(s) with frequencies equal to the Bloch frequency divided by an integer is applied to the carrier transport media to alter the effective barriers of the impurities or barrier structures to an arbitrarily large potential compared to the zero field barrier potential. The various impurities or barrier structures are band engineered and deposited, grown or implanted in the carrier transport media and can take any form such as barrier layers in or on the transport media, laterally induced barriers, and impurities or defects in the carrier transport media. The application of time-dependent external fields across a length of nanoscale or mesoscopic structure leads to an effective renominalization of the barrier potential strengths when the frequency of the applied electric field multiplied by an integer is equal to the Bloch frequency. Under these conditions the transmission probability is altered and the current ratio, i.sub.2 /i.sub.1, will be modulated strongly.

Field controlled current modulators based on tunable barrier strengths

A semiconductor lasing device is formed by disposing a quantum well or quum wire array between positive and negative ohmic contacts such that different potentials are applied along the array to establish a transverse electromagnetic (TEM) mode of the optic signal (i.e. where the field components lie in a plane perpendicular to the direction of propagation). Thus, the light confinement l will be on the order of the electron confinement a. By applying different potentials via the positive and negative ohmic contacts to multiply connected waveguides, the established TEM mode does not have a cut-off frequency, and therefore, the gain of device can be greatly enhanced while still providing increased anisotropy and a low threshold current.

TEM mode quantum wire or well structure

A submatrix of semiconductor material contains plural electron conduction annels in either or both series and parallel arrangements. Electrons in the channels are confined by the submatrix and a surrounding main matrix provides photon confinement within the submatrix for nonequilibrium phonons which are mutually interchanged between channels. The confinement enhances the efficiency of energy and momentum transfer by means of nonequilibrium phonons. Embodiments of the invention as a transformer, bistable switch, controlled switch and amplifier are disclosed.

Interchannel nonequilibrium confined-phonon exchange device

An thermal imaging device having a transparent substrate, an active multiple quantum well (MQW) epilayer with bottom electrical contacts bonded to the substrate, wherein the substrate is cut such that its thermal expansion coefficient is matched or roughly matched to that of the MQW epilayer in the direction parallel to the long axis of the bottom contacts and so that the thermal expansion coefficient of the substrate is mismatched in a direction normal to the long axis of the bottom contacts. Infrared radiation incident on each unit cell of the n.times.m array will produce a temperature change .DELTA.T in the MQW which will produce stress normal to the long axis of the bottom contacts. The uniaxial stress produced by the temperature changes .DELTA.T breaks the rotation symmetry in the plane of the MQW structure. This will result in anisotropic mixing of the heavy and light holes in the MQW epilayer and thus, will result in an anisotropic excitonic absorption of the MQW epilayer, which can be detected and analyzed either electrically or optically.

Infrared imaging array based on temperature driven anisotropic optical

A quantum wire embedded in another material or a quantum wire which is free standing. Specifically, the quantum wire structure is fabricated such that a quantum well semiconductor material, for example Gallium Arsenide (GaAS), is embedded in a quantum barrier semiconductor material, for example Aluminum Arsenide (AlAs). Preferably, the entire quantum wire structure is engineered to form multiple subbands and is limited to a low dimensional quantum structure. The dimensions of the quantum wire structure are preferably around 150.times.250 .ANG.. This structure has a negative absolute conductance at a predetermined voltage and temperature. As a result of the resonant behavior of the density of states, the rates of electron scattering in the passive region (acoustic phonon and ionized impurity scattering as well as absorption of optical phonons) decrease dramatically as the electron kinetic energy increases.

Negative absolute conductance device and method

An optic modulator having a transparent piezoelectric substrate, an active multiple quantum well (MQW) epilayer with bottom electrical contacts bonded to the substrate, wherein the substrate is cut such that its thermal expansion coefficient is matched or roughly matched to that of the MQW epilayer in the direction parallel to the long axes of the bottom contacts and so that the piezoelectrically-active direction of the substrate is normal to the long axes of the bottom contacts. In order to control the bias of the MQW epilayer a transparent contact is disposed over the MQW epilayer. In operation, the piezoelectric substrate, when activated, will displace an anisotropic strain on the MQW epilayer which will break the rotational symmetry in the plane of the MQW. This will result in anisotropic mixing of the heavy and light holes in the MQW epilayer and thus, will result in an anisotropic excitonic absorption of light normal to the MQW epilayer.

Optical modulator based on piezoelectrically driven anisotropic optical

A phonon modulator which includes a semiconductor body having at least first and second polar semiconductor quantum wells formed therein separated by a polar semiconductor barrier. The conduction band energies of the wells and barrier are selected such that the lowest energy electronic states in the two wells are separated by an energy which is greater than the energies of optical phonons in the well and barrier materials. Respective voltages are applied to the wells which are less than the optical phonon emission threshold in the well and barrier materials to generate respective currents therein. Increasing the voltage to the first well to a level in excess of such optical phonon emission threshold causes optical phonons to be emitted from the first well to create a standing interface mode from the first well through the barrier to the second well, thereby providing a scattering mechanism for electrons in the second well and reducing the current thereof.

Quantum well phonon modulator

A polar semiconductor quantum wire for use in electronic and opto-electronic devices. The polar semiconductor quantum wire is either completely or partially encapsulated in metal to reduce the strength of the scattering potential associated with interface optical phonons normally established at the lateral boundaries of polar semiconductor quantum wires. Metal alone or metal employed in conjunction with modulation doping enhances the transport of charge carriers within the polar semiconductor quantum wire.

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Durham, NC, United States of America

Michael A Stroscio