Abstract: A high-resolution scanning probe microscope using a coherent dual-tip probe comprises two single-atom protrusions on a single crystal metal wire. As the dual-tip probe scans across the surface of a sample material under an electrical bias, an interferenced electron wave function formed by two protruding atoms interacts with electron wave functions of the sample surface. Such an interferenced wave function has a distinctive pattern of electron wave density as high as four times that of a single-atom tip. A more distinctive microscopic image of the sample surface is therefore generated. The resolution of the dual-tip scanning probe microscopic image is also higher than that obtained by a single-tip probe because the interferenced electron wave function provides a confined and densely distributed interactive region.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: Multidimensional quantum-well arrays are made by electron-beam lithographic atterning, followed by solid-state diffusion.

Abstract: A multi-terminal Group III-V semiconductor high electron mobility field effect transistor comprised of a sandwich of molecular beam epitaxially grown layers and including two high mobility charge flow channels in respective two dimensional electron gas regions implemented, for example, by at least one doped layer of aluminum gallium arsenide adjacent an undoped gallium arsenide layer separated by a heterojunction. A pair of opposing two dimensional electron gas (2DEG) regions are generated in the layer of undoped gallium arsenide by the bending of the energy levels of the semiconductor materials. Charge flow occurs in a unidirectional fashion from one channel to the other in the common undoped gallium arsenide layer under the control of an electric field applied transversely through the structure by means of a top gate electrode and a bottom field plate electrode.

Abstract: An electronic oscillator being operable to detect millimeter wave and infrared frequency output signals over the range of 1-1000 GHz consists of a semiconductor device having a structure comprised of a first planar doped barrier region separated from a second planar doped barrier region by a superlattice region. Upon the application of a uniform electric field, the first planar doped barrier region operates as a means for injecting electrons into the superlattice region which then traverse to the second planar doped barrier region which operates as means for receiving the electrons. During transit through the superlattice region, the electrons undergo an oscillatory motion thereby making possible the detection of signals whose frequency is a function of the applied voltage and the periodic spacing of the superlattice.

Abstract: A transferred electron semiconductor device in the form of an oscillator, for example, is fabricated by a molecular beam epitaxy growth process wherein a plurality of semiconductor layers are sequentially grown on a planar substrate. A pair of ohmic contacts are formed on the outer surface of the substrate and the uppermost layer with the resulting structure including two distinct intermediate semiconductor regions, the first being a drift region adapted to exhibit a differential negative resistance due to the transferred electron effect, and the second being a planar doped barrier region for accelerating electrons into the upper valley and injecting them into the drift region. By the use of a planar doped barrier a more uniform electric field is obtained along with a controlled lower barrier height whereby the transfer of electrons to the upper conduction band satellite valley can be made to occur over much shorter times and distances thus extending the upper frequency range of operation.

Abstract: A superlattice semiconductor device consisting of a plurality of multi-dimensional charge carrier confinement regions of semiconductor material exhibiting relatively high charge carrier mobility and a low band gap which are laterally located in a single planar layer of semiconductor material exhibiting a relatively low charge carrier mobility and high band gap and wherein the confinement regions have sizes and mutual separation substantially equal to or less than the appropriate deBroglie wavelength. The device, in its preferred form, comprises a thin film of semiconductor material selected from group II-VI or III-V compounds or silicon wherein there is formed laterally located cylindrically shaped periodic regions which are adapted to act as quantum well confinement regions for electrons.

Abstract: The use of fabricated periodic piezoelectric structures fabricated from h resistivity semiconducting crystals in detecting millimeter waves in the GHz range is disclosed.

Abstract: Methods and apparatus for contactless, non-destructive resistivity measurnts on semiconducting crystalline material, for example gallium arsenide. The material to be tested is formed into a disc which is supported within an air gap. The holder for the disc is such as to support the disc only about its outer edges; thus, the disc is free to vibrate piezoelectrically. A measuring circuit connected to the electrodes, which establish the air gap, applies an alternating electric field in the air gap which causes the crystal to vibrate. By adjusting the frequency of excitation, resonance may be established in the crystal and by comparing the current drawn through the air gap with graphs previously established for material of the type under test, the resistivity of the disc can be determined.