In this article we review the experimental and theoretical investigations of the linear and nonlinear optical properties of semiconductor quantum well structures, including the effects of electrostatic fields, extrinsic carriers and real or virtual photocarriers.

Linear and nonlinear optical properties of semiconductor quantum wells

Oscillations have been obtained at frequencies from 100 to 712 GHz in InAs/AlSb double‐barrier resonant‐tunneling diodes at room temperature. The measured power density at 360 GHz was 90 W cm−2, which is 50 times that generated by GaAs/AlAs diodes at essentially the same frequency. The oscillation at 712 GHz represents the highest frequency reported to date from a solid‐state electronic oscillator at room temperature.

Oscillations up to 712 GHz in InAs/AlSb resonant‐tunneling diodes

This paper provides an overview of research developments toward nanometer-scale electronic switching devices for use in building ultra-densely integrated electronic computers. Specifically, two classes of alternatives to the field-effect transistor are considered: (1) quantum-effect and single-electron solid-state devices and (2) molecular electronic devices. A taxonomy of devices in each class is provided, operational principles are described and compared for the various types of devices, and the literature about each is surveyed. This information is presented in nonmathematical terms intended for a general, technically interested readership.

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Overview of nanoelectronic devices

We describe a new family of clocked logic gates based on the resonant-tunneling diode (RTD). Pairs of RTDs form storage latches, and these are connected by networks consisting of field-effect transistors (FETs), saturated resistors, and RTDs. The design, operation, and expected performance of both a shift register and a matched filter using this logic are discussed. Simulations show that the RTD circuits can achieve higher performance in terms of speed and power in many signal processing applications. Compared to circuits using III-V FETs alone, the RTD circuits are expected to run nearly twice as fast at the same power or at the same speed with reduced power. Compared to circuits using Lincoln Laboratory's fully depleted silicon-on-insulator CMOS, implementation using state-of-the-art RTDs should operate five times faster when both technologies follow the CMOS design rules.

A new RTD-FET logic family

While most of the electronics industry is dependent on the ever-decreasing size of lithographic tran- sistors, this scaling cannot continue indefinitely. Nanoelectro- nics (circuits built with components on the scale of 10 nm) seem to be the most promising successor to lithographic based ICs. Molecular-scale devices including diodes, bistable switches, carbon nanotubes, and nanowires have been fab- ricated and characterized in chemistry labs. Techniques for self-assembling these devices into different architectures have also been demonstrated and used to build small-scale proto- types. While these devices and assembly techniques will lead to nanoscale electronics, they also have the drawback of being prone to defects and transient faults. Fault-tolerance techni- ques will be crucial to the use of nanoelectronics. Lastly, changes to the software tools that support the fabrication and use of ICs will be needed to extend them to support nano- electronics. This paper introduces nanoelectronics and reviews the current progress made in research in the areas of tech- nologies, architectures, fault tolerance, and software tools.

The Future of Integrated Circuits: A Survey of Nanoelectronics Nano-devices, such as molecules that function as computer switches as well as silicon wires and carbon tube interconnections, have been fabricated and demonstrated, and further research is underway.

Picosecond bistable operation has been experimentally observed for the first time in a double‐barrier resonant tunneling diode. A rise time of 2 ps was measured using the electro‐optic sampling technique; this is the fastest switching event yet observed for an electronic device. This time domain measurement adds necessary information to the understanding of the transport mechanisms in the resonant tunneling diode and is consistent with switching time limitations computed for the device. It also demonstrates that appropriately designed double‐barrier quantum well diodes have a response time comparable to that of the fastest all‐optical logic elements, and that they may be very useful in high‐speed logic applications.

Picosecond switching time measurement of a resonant tunneling diode

Optical spectra near the band edges of AlxGa1−xAs/GaAs coupled quantum well structures are found to exhibit rich structure. Under the Stark perturbation, these transitions have behavior remarkably different from those associated with single quantum wells. Positive energy shifts and high sensitivity to electric fields have been observed and interpreted as evidence of well coupling. Results of a simple numerical calculation support this interpretation.

Stark effect in AlxGa1−xAs/GaAs coupled quantum wells

Semiconductor quantum wells (QWs) have been shown to be important for application to electrooptic (EO) modulators.1 Single QWs, however, are structurally too simple for engineering electroabsorption properties, such as large modulation depth with small applied fields.

Stark effect in AlxGa1-xAs/GaAs coupled quantum wells

Tunneling-time measurements on a heterojunction double-barrier resonant tunneling diode (RTD) have been made using electro-optic sampling techniques. Quantum- mechanical tunneling in these single quantum wells is the fastest known charge-transport mechanism in semiconductors. This class of device exhibits such features as negative differential resistance (NDR), an extremely fast current response,1 and a high-frequency output when applied as an oscillator.2 Now, using a laser-based sampling system having a demonstrated subpicosecond temporal response,3 a switching time of less than 2 ps has been measured for a double-barrier RTD. This measurement indicates the potential utility of these diodes as high-speed logic devices4 and helps explain the tunneling mechanisms involved.

W. D. Goodhue

Papers

Picosecond switching time measurement of a resonant tunneling diode

Stark effect in AlxGa1−xAs/GaAs coupled quantum wells

Stark effect in AlxGa1-xAs/GaAs coupled quantum wells

Tunneling-Time Measurements of a Resonant Tunneling Diode