Information is about to be freed from its dependence on wires * But no single company has all the assets it will need to dominate this emerging market * And to win long-term advantages, the sophisticated use of customer information will be essential Wireless information delivery has been around for a long time - indeed, since the first words spoken by human beings. More recently, Wireless information has been transmitted through military walkie-talkies and two-way police radios. And now, with the development of wireless devices that can log on to the Internet and send and receive data, wireless communication is joining, the digital age. Soon you will be able to use wireless services to easily check up on your stock portfolio, log on to your company intranet, check the weather in cities you visit, and read about restaurants where you might wish to eat. These developments are the result of improved mobile networks, the emergence of open Internet-based standards, and better technology for handheld devices. The upshot is that the market for wireless information is finally taking off. Sources of content are proliferating at an explosive rate [ILLUSTRATION FOR EXHIBIT 1 OMITTED], along with Internet and e-mail usage. Meanwhile, the number of professional people who spend time outside their offices is increasing [ILLUSTRATION FOR EXHIBIT 2 OMITTED], and they need portable devices to stay in touch [ILLUSTRATION FOR EXHIBIT 3 OMITTED]. By 2003, there could be 60 million users of wireless-data services in North America, and the market could be worth up to $10 billion. Of course, companies are scrambling to take advantage of this opportunity. Cisco and Motorola, for instance, have announced plans to develop and build wireless networks based on the Internet Protocol(*) (IP). Qualcomm and Ericsson have agreed jointly to support and license a single world standard for the next generation of wireless communications, and this will surely speed the development of wireless-data capabilities. Behind the deals and alliances is a growing awareness that no single player has all of the assets needed to dominate this emerging market. Such natural competitors as content providers, software companies, wireless-service providers, and equipment and device manufacturers will have to work together. Two factors will be decisive: gaining market share quickly by creating a complete wireless-data service and encouraging loyalty among customers by using information about them in a savvy way. How wireless data finally became a reality Three barriers prevented the earlier and wider adoption of wireless-data services. Wireless networks were originally built to carry voice traffic; as a result, their ability to carry data was limited. This problem was addressed at first through the use of overlays of digital protocols on existing analog cellular networks.(**) The new generation of wireless networks is being built on more data-friendly digital platforms, such as Code Division Multiple Access (CDMA) and the Global System for Mobile Communications (GSM). They make it easier to add packet-data protocols and to provide higher speeds. The second barrier was the absence of standards. Without them, developing and rolling out wireless-data applications has been both difficult and costly. Now, however, the creation of wireless support for Internet protocols is solving the problem. Although IP-based platforms and flexible interfaces were designed for wireline environments, they have been adapted to the needs of wireless. Currently, a number of applications are successfully taking shape. Meanwhile, additional enablers for wireless have been developed, such as the Wireless Markup Language (WML), a version of the HyperText Markup Language (HTML), which is used to design pages for the World Wide Web. WML makes it possible to adapt Web-based content for display across a range of devices with limited memory and small screens. …

We have observed a far-infrared (0.3–2.5 THz) radiation-induced photovoltaic signal in an antenna-coupled quantum point contract, which oscillates with the gate voltage and peaks at the onset of each subband. The polarity of this photovoltaic signal can be reversed by shifting the far-infrared beam from the drain to the source, or vice versa. This signal has been unambiguously attributed to thermopower generated by asymmetric heating of the drain and the source by the far-infrared radiation. Quantitative agreement has been obtained between measurements and calculations based on ballistic transport in one-dimensional electron systems and the electrical and thermal circuit elements in our experimental system.

Results of transport measurements on a GaAs quantum dot are presented in which the gate geometry allows the dot to be accessed by three, rather than two, contacts. In the Coulomb blockade regime, conductance oscillations periodic in gate voltage are measured concurrently at two contacts in response to a small excitation voltage at the third contact. When the dot is in the strongly blockaded regime, we obtain the expected result from single electron tunneling theory that oscillations at the two output contacts are correlated with each other in gate voltage. As the tunnel barriers are made softer by changing the gate voltage, a strikingly different phenomenon is observed: conductance peaks at the two output leads evolve from perfect correlation to perfect anticorrelation with each other.

In our quest to demonstrate electron directional coupling, the coherent tunneling of electrons between two electron waveguides, we have investigated split-gate dual electron waveguide devices. With the structure biased in a ''leaky'' electron waveguide configuration we have carried out extensive observations of one-dimensional (1D) to two-dimensional (2D) tunneling between a waveguide and a neighboring two-dimensional electron gas. These tunneling spectroscopy experiments have provided the first glimpse of the one-dimensional density of states of a 1D electronic system. We have also carried out experimental observations of 1D to 1D tunneling between two electron waveguides. Demonstrating electron directional coupling will still require the development of a new generation of ultrashallow heterostructures with sharp confining potential barriers.

We report the observation of controlled electron tunnelling between two closely spaced one-dimensional (1D) electron waveguides implemented using a split-gate scheme on a high mobility AlGaAs/GaAs heterostructure. The 1D to 1D tunnelling current shows a distinct bumpy pattern when the electronic subband population in the two waveguides is modulated. These results are consistent with a picture in which tunnelling primarily occurs when the 1D subbands in both waveguides line up in energy as expected from energy and momentum conservation rules.

The discovery of electron waveguiding in one-dimensional (1D) semiconductor nanostructures has uncovered a new regime of electron transport with fascinating physics. The device potential of electron waveguides, however, remains largely unexplored. Over the last few years, our interuniversity team has been conducting research on the physics, technology and opportunities for device applications of split-gate AlGaAs/GaAs electron waveguides. We have examined electronic devices based on electron transport, tunneling and interference. Many problems have been identified in transport-type devices, but much more research is required before the engineering potential of tunneling and interference devices is understood. We have also investigated the potential of electron waveguides in photonic applications, with emphasis on far-infrared (or THz) photodetectors. Our research to date has revealed strong photon-induced currents in antenna-coupled electron waveguides that arise from quantum thermopower. Far-infrared photodetectors based on photon-induced quantum transport remain an interesting opportunity for the application of electron waveguides.

We are developing a novel submillimeter-wave and THz detector using semiconductor quantum point contacts. The operation principle of this unique device is based on a new physical phenomenon, called photon-assisted quantum transport,' in which photons efihance the energy of ballistic transport electrons and produce a photon-induced drain/source current A quantum point contact is formed by depleting the 2DEG (two-dimensional electron gas) underneath a split-gate electrode on a MODFET (modulation-doped field-effect transistor) structure. For our device, the split-gate also serves as the two terminals of a planar antenna which concentrates the radiation field in the point contact region. The electrical field of the radiation near the split-gate is orthogonal to the drain/source conduction path. Intersubband transitions can therefore be excited that contribute to the drain/source conduction. It is estimated in our theory that the current responsivity of the quantum point contact detectors can be comparable to the quantum efficiency e/fiti) at and above 1 THz. The capacitance of this device should be small due to the planar geometry. Thus, the RC roll-off, which is inevitable in all tunnel devices such as SIS junctions and Schottky diodes, is negligible. Consequently, a very high-frequency quantum photon detector (.. .1 THz) could be developed. We have fabricated several quantum point contacts with antenna/split-gate structures using a combination of optical and electron-beam lithography on a GaAsiAlGaAs MODFET structure with a 2D electron density 2.8x10 11 cm-, and an electron mobility 200,000 cni/Visec at 45 K. Under a 300 Gliz coherent radiation at about 0.5 mW level, a profound photon-induced drain/source current is produced throughout the entire gate voltage region in which the quantum point contact exhibits the behavior of an 1D electron system. The amplitude of the photon-induced current is comparable to that corresponding to a quantized conductance step, i.e. (2e 1h)VDS, and it oscillates with the gate voltage. Our analysis suggests that the photon-induced drain/source current is mainly due to heating (or a bolometric effect). Future improvement of device parameters are discussed. Page 606 Fourth International Symposium on Space Terahertz Technology

We present a comprehensive experimental study of the tunneling and transport characteristics of split-gate ``leaky'' one-dimensional (1D) electron waveguides implemented in ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/GaAs heterostructures. In a leaky electron waveguide, electrons can tunnel out of the 1D channel through a thin side wall barrier into an adjacent 2D electron bath. A sharp peak and valley structure is observed in the 1D-to-2D tunneling current as the carrier concentration is modulated in the 1D waveguide through the field-effect action of the split gates. A semiclassical model confirms that the tunneling features originate from the 1D subbands in the channel.

The authors report the first unambiguous observation of controlled electron tunneling between two closely spaced 1D electron waveguides. This represents a significant step toward the realization of a quantum field-effect electron directional coupler (QFED). The authors have fabricated a variety of dual electron waveguide devices with different lengths and widths on an AlGaAs/GaAs heterostructure (...

We have demonstrated a novel analog-to-digital (A:D) conversion architecture based on the quantized conductance of electron waveguides. In our scheme, a dual electron waveguide (DWG) device implements a binary quantizer and encoder for one significant bit. The conductance values of the on and off states are 2e/sup 2//h and zero, respectively. By cascading multiple DWG devices, higher order bits can be attained. In this paper, we demonstrate the first significant bit and the second significant bit for a 2-bit analog-to-digital converter using a DWG device fabricated in an AlGaAs/GaAs modulation-doped heterostructure.<>

Motivated by the recently developed theory of photon-assisted quantum transport, we have studied transport properties of an antenna-coupled quantum point contract under coherent far-infrared (285 GHz) radiation. A pronounced photon-induced drain/source current is observed. The amplitude of the photon-induced current is about 10% of that corresponding to a quantized conductance step, and it oscillates with the gate voltage. Our analysis suggests that the observed photon-induced current is mainly due to heating of the electron gas in the source and drain (a bolometric effect) rather than photon-assisted quantum transport. Future improvement of the device parameters to enhance the effect of photon-assisted transport will be discussed.

Using an AlGaAs/GaAs modulation-doped heterostructure, we have fabricated a novel split-gate electron waveguide with a thin gate as one of its confining electrodes. This scheme implements a ''leaky'' waveguide out of which electrons can tunnel through the thin side-wall. The resulting tunneling current shows strong oscillations as the electron concentration in the waveguide is modulated. This result is attributed to a direct observation of the one-dimensional density of states of the electron waveguide.

Contains reports on four research projects, the research facility and a list of publications.

We report on the fabrication of AlGaAs/GaAs split-gate electron waveguide devices of lengths between 0.1 and 2 μm using x-ray lithography, and the measurements of these devices at liquid-helium temperatures and up to 15 K. An x-ray mask (parent mask) was fabricated using e-beam lithography and replicated using proximity x-ray lithography (λ=1.32 nm) to generate a replica (daughter) mask. The daughter mask was then aligned to patterns on a high-mobility AlGaAs/GaAs sample and x ray exposed using a conformable mask fixture. The conductance of the electron waveguides was measured as a function of the split-gate bias. Sharp 2e2/h conductance steps were observed in devices up to 0.75 μm long at T=2 K. The features in the conductance remain visible up to 15 K.

The effects of single scatterers on the transport and tunneling characteristics of a dual-electron-waveguide device have been studied. We observe a dramatic degradation in the quantized conductance steps of the waveguides as the one-dimensional channel is electrostatically steered into a scatterer. By analyzing the magnitude and shape of the quantized conductance steps for different lateral regions between the confining split gates, we are able to pinpoint the location of the scatterers in the device. In addition, the oscillations in the tunneling current out of one of the waveguides are found to also be very sensitive to the presence of a single scatterer within the waveguide and in the tunneling region.

It is shown that a severe degradation in the quantum-effect features occurs when only a single impurity exists in the device. Transport in different lateral regions of the waveguide is studied for a 0.5- mu m-long, 0.3- mu m-wide waveguide. As the waveguide is opened to include a single impurity, an immediate and drastic degradation in the conductance steps is observed, because the presence of the...

A split-gate technology on an AlGaAs/GaAs heterostructure is used to implement a novel quantum-effect device which allows two electron waveguides to come into very close proximity to each other over a certain length. The field-effect action of a middle gate controls the height and width of the energy barrier between the waveguides. This allows a gradual transition from two isolated waveguides to two closely spaced waveguides and finally to the merging of both waveguides into a single broad waveguide. Two side gates can control the number of occupied subbands in each waveguide. This is confirmed by the observation of sharp 2e2/h conductance steps in each waveguide at 1.8 K as the side-gate voltage is modulated.