J. H. Abeles

High‐frequency amplification and generation in charge injection devices

Room‐temperature high‐frequency measurements on a three‐terminal amplifying device based on real‐space hot‐electron transfer between two conducting layers separated by a potential barrier have been performed. The devices grown by organometallic chemical vapor deposition utilize a novel undoped GaAs/AlGaAs heterostructure which, through its dramatically reduced parasitic leakage compared to previous structures, permits, for the first time, operation as a charge injection transistor. The charge injection transistor exhibits true three‐terminal amplification due to real‐space hot‐electron transfer controlled by electron temperature in a high mobility channel. The device demonstrates power and current gains with cut‐off frequencies of 9.8 and 29 GHz, respectively, with maximum current gain of 39 dB. In the negative resistance transistor mode, the same device was found capable of microwave generation up to 7.7 GHz. The frequency response of our device is shown to be limited by RC in the output circuit and meth...

High‐speed electrical sampling by fs photoemission

We propose and demonstrate a new method for contactless sampling of high‐speed electrical signals, by spectral analysis of photoelectrons emitted when a signal‐carrying conductor is illuminated by ultrashort light pulses. We present time‐resolved measurements of sub‐ns electrical signals on a gold transmission line on GaAs using three‐photon photoemission induced by 80 fs visible laser pulses, and we discuss the temporal resolution of these measurements. This method is applicable to devices and circuits on any semiconductor.

Suppression of sidelobes in the far‐field radiation patterns of optical waveguide arrays

Arrays of coherent optical emitters are attractive for high‐speed, wide‐angle optical beamsteering or deflection, but uniform arrays radiate undesirable sidelobes. It is shown that dramatic suppression of sidelobes can be accomplished by configuring emitters in a nonuniform pattern. A nearly optimum radiation pattern for scanning results from gradually doubling the interelement spacing across a one‐dimensional array. As an example, a 100‐element waveguide array of minimum interelement spacing 5 μm radiates a 0.08° main lobe (full width at half‐maximum) with a 30× suppression of sidelobe intensity.

Novel optoelectronic single quantum well devices based on electron bleaching of exciton absorption

Novel planar optoelectronic devices with two‐dimensional exciton absorption controlled by free‐carrier‐induced bleaching are proposed. Exciton‐resonant light propagates along a single mode rib waveguide containing a single quantum well (SQW), the only absorbing medium in the waveguide. Three such devices operating as optical modulators are (1) a gate‐controlled field‐effect transistor optical modulator (FETOM), (2) an optically readable memory element, and (3) an optically switched charge storage device. The FETOM, in which free‐carrier density in the SQW is controlled by gate voltage, offers high speed (37.5 ps), small size (125 μm), and low power (86 nW/MHz).

Junction field‐effect transistor single quantum well optical waveguide modulator employing the two‐dimensional Moss–Burstein effect

A modulation‐doped junction field‐effect transistor incorporating an optical waveguide under the gate modulates light by the carrier band‐filling effect (two‐dimensional Moss–Burstein effect) in a single quantum well, achieving a 5:1 extinction ratio in a 250‐μm‐long waveguide for 4 V reverse gate‐source bias Vgs swing and 0 V drain‐source bias Vds. Similar performance is obtained over a 16 nm spectral range. A novel band‐edge transparency effect is observed for Vds>0 allowing an extinction ratio of 10:1, corresponding to a change in absorption of 92 cm−1 to be obtained through band‐gap dilation by hot electrons at biases of Vds =8 V. Below‐band‐gap refractive index modulation of 1.6×10−3 is obtained for a Vgs swing of 2.4 V. The novel junction field‐effect transistor optical modulator also functions as a photovoltaic or photoconductive optical detector, a transistor, and a light‐emitting diode.

Nonlinear high‐frequency response of GaAs metal‐semiconductor field‐effect transistors

Calculations show that phase nonlinearity in 1 μm gate length power GaAs metal‐semiconductor field‐effect transistors (MESFET’s) can be accounted for by the variation of gate‐channel capacitance with gate bias voltage. Buried‐layer GaAs MESFET’s having constant gate‐channel capacitance have been fabricated and their high‐frequency linearity measured. The devices display dramatic reductions of phase nonlinearity to 0.15°/W output power at 6 GHz for powers below saturation in 8 mm gate‐width devices confirming that nonlinear capacitance causes nonlinearity observed in conventional GaAs MESFET’s. Channel transit time, estimated at 3–6 ps, is not significant as a cause of nonlinearity and varies less than 100 fs with signal level.

Characterization of Al/sub 0.3/Ga/sub 0.7/As/GaAs quantum-well delta-doped channel FET grown by molecular-beam epitaxy

Summary form only given. The authors investigated the transport properties of electrons in delta-doped channels formed both in bulk GaAs and in quantum wells by Hall and Schubnikov-de Haas measurements. They also investigated the DC and microwave characteristics of FETs made from Al/sub 0.3/Ga/sub 0.7/As/GaAs heterostructures with a quantum-well delta-doped channel. FETs showed a high drain current capability, large breakdown voltage, low output conductance, large intrinsic transconductance, and large gate voltage swing around maximum transconductance. >

Experimental measurement of a high‐field dipole in GaAs field‐effect transistors

GaAs short channel metal‐semiconductor field‐effect transistor models predict the formation of a high‐field dipole layer with current saturation. In this work, the formation of such a dipole at the onset of current saturation is experimentally verified through measurement of the high‐frequency conductivity of the channel. The complex conductivity and its dependence on frequency are analyzed to yield the capacitance of the high‐field domain and its dependence on source‐drain voltage. The corresponding peak electric field in the domain is ∼1.5×105 V/cm under current saturation conditions. The implications of the formation of such a domain on the speed of response of these devices are discussed.

Novel single quantum well optoelectronic devices based on exciton bleaching

Novel planar high-speed optoelectronic devices offering advantages for optoelectronic integration are proposed. Exciton-resonant light propagates along a single-mode rib waveguide containing a single quantum well (SQW), the only absorbing medium in the waveguide. The two-dimensional (2D) excitonic optical absorption is controlled by the bleaching effect induced by free carriers, whose electrical conduction simultaneously makes possible optical detection and high-speed transistor action. Three such optical modulating devices are: 1) a gate-controlled single quantum well field-effect transistor (FET) optical modulator (FETOM), 2) an optically-readable memory element, and 3) an optically-switched charge storage device. The FETOM, in which the free-carrier density in the SQW is controlled by the gate voltage, offers high speed (22 ps), small size (125 μm), and unique potential for optoelectronic integration.

Langmuir-Blodgett Deposited Gates For InP-InGaAs Field Effect Transistors

We report on the novel application of Langmuir-Blodgett film deposition of cadmium di-stearate to form a high barrier height Schottky barrier on n-In0.53Ga0.47As. The method is simple and can be applied to integrated optoelectronics where conflicting device requirements impose astringent constraints on the material and processing technology. Using this technique to form the gate electrode, we fabricated a 1μm gate length inverted InP-InGaAs modulation doped field effect transistor (MODFET) with an extrinsic transconductance of 170 mS/mm and a current gain cut-off frequency fT of 19 GHz.