Alexander Kastalsky

New infrared detector on a silicon chip

We report a single-crystal Si-Ge structure which works as an efficient photodetector in the wavelength region of up to 1.5 µm. The multilevel structure is grown by molecular-beam epitaxy on an n-type 3-in silicon substrate and consists of the following layers: n+silicon (1000 Å), n+GexSi1 - xalloy (1800 Å, graded in ten steps fromx = 0tox = 1), n+germanium (1.25 µm), undoped germanium (2.0 µm), and p+germanium (2500 Å). Top three layers form a germanium p-i-n diode, which is removed from the Ge-Si interface by a buffer layer of high conductivity. An advantage of this structure is that its performance is insensitive to material defects in the buffer layers. Moreover, transmission electron microscopy shows that the density of dislocations introduced by lattice mismatch at the Ge-Si interface falls off with the separation from the interface. Our first experimental structures do exhibit the characteristics of a germanium p-i-n diode. The spectral response curves agree with those given in the literature for germanium, both at room and liquid nitrogen temperatures. For the incident light wavelength of 1.45 µm we have measured a quantum efficiency of 41 percent at T = 300 K. we believe that our approach opens an attractive possibility of fabricating complete infrared optoelectronic systems on a silicon chip.

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...

Hot electron injection devices

Recently we proposed a novel three-terminal structure which employs hot-electron transfer between two conducting layers separated by a potential barrier and contacted individually. Several new device concepts based on this principle have been demonstrated experimentally. In the present work we review these devices —a charge injection transistor, a negative-resistance microwave oscillator controlled by a third terminal, and a memory element — emphasizing the physics of their operation.

HOT-ELECTRON TRANSPORT IN HETEROSTRUCTURE DEVICES

Abstract A number of hot-electron device concepts are reviewed with the emphasis on their potential for applications and the limitations. The discussion is restricted to charge-injection devices, i.e., those in which hot electrons are transported either ballistically or thermionically between adjacent layers. Recent developments related to the metal-base transistor and its all-semiconductor analogs, as well as those related to the real-space-transfer effect in heterolayers, are critically reviewed.

Theory of hot-electron injection in CHINT/NERFET devices

We have considered theoretically the basic physical processes underlying the operation of the charge injection transistor (CHINT) and the negative resistance field-effect transistor (NERFET). Our treatment is based on the electron temperature (Te) approximation for the energy distribution of hot electrons in the two-dimensional electron gas (2DEG) channel. The Teis determined from an energy-balance equation which includes the following processes: 1) electron heating by the source-drain electric field (assumed uniform), 2) energy losses due to the interaction with phonons, 3) energy losses due to the emission of hot electrons from the channel into the second conducting layer (collector) and the attendant nonconservation of the channel current. Our theory gives a semi-quantitative analytical description of the current-voltage characteristics of CHINT/NERFET devices. Most--but not all-- of the important experimental features of the device operation are adequately described. Further improvement of the theory should include a realistic description of the field nonuniformity along the channel.

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.

Novel high-speed transistor based on charge emission from a quantum well

A novel unipolar transistor employing properties of electrons confined in a single quantum well is proposed. The gate modulation of a charge density in the quantum well results in an exponentially strong variation of the output thermionic emission current to the collector. The device combines the attractive features of both bipolar and field‐effect transistors and provides a high speed (2–3 ps intrinsic delay time) with a large current drive (∼105 A/cm2) and high transconductances (1–10 S/mm).

Nonlinear transport phenomena in a triangular quantum well

We have measured transport properties in an AlGaAs/AlxGa1−xAs, triangular quantum well whose energy spectrum has been varied by means of gate bias. We have observed several nonlinear effects in the lateral conductance arising at positive gate voltages as the increasing Fermi level is moved toward the lowering energy positions of the excited subbands in the quantum well. We interpret our results in terms of electron population of the excited subbands in which electrons possess low mobility. Finally, we find new features at high lateral voltages which are considered to be an evidence of previous predicted electrophonon resonance.

Quantum well tunnel triode

We demonstrate a novel three‐terminal device, the tunnel triode, in which the current within the quantum well is a part of the tunnel current through the p+‐n+ junction. A tunnel‐diode‐like negative differential resistance effect with peak‐to‐valley ratio as high as 20 was observed, the tunnel current being controlled by the gate voltage. We show that tunneling occurs not in the quantum well, but in the heavily doped n+‐Al0.3Ga0.7As layer, and it is preceded by a real‐space hot‐electron transfer from the quantum well into this layer. Logic operation of a bistable switch was obtained in a circuit comprising a tunnel triode and a series resistance.