P. Omling

Unidirectional electron flow in a nanometer-scale semiconductor channel: A self-switching device

By tailoring the boundary of a narrow semiconductor channel to break its symmetry, we have realized a type of nanometer-scale nonlinear device, which we refer to as self-switching device (SSD). An applied voltage V not only changes the potential profile along the channel direction, but also either widens or narrows the effective channel depending on the sign of V. This results in a diode-like characteristic but without the use of any doping junction or barrier structure. The turn-on voltage can also be widely tuned from virtually zero to more than 10 V, by simply adjusting the channel width. The planar and two-terminal structure of the SSD also allows SSD-based circuits to be realized by only one step of lithography.

Hole photoionization cross sections of EL2 in GaAs

The spectral dependence of the hole photoionization cross section σ0p of EL2 in GaAs has been determined in absolute numbers at T=78 and 295 K. From simultaneous measurements of the electron photoionization cross section σ0n, accurate values of the photon energies and the cross sections at which σ0n=σ0p could be obtained. These data are of importance for rapid and accurate determination of concentration and charge states of EL2 in GaAs, e.g., in wafer mapping applications.

Nonlinear operation of GaInAs/InP-based three-terminal ballistic junctions

We report on nonlinear electrical properties of three-terminal ballistic junctions (TBJs) based on high-electron-mobility GaInAs/InP quantum-well structures. Nonlinear electrical transport behavior of the TBJs is found, and we show a correlation between this behavior and the linear regime of electron transmission in the devices. We also study device geometry effects on these electrical properties of the TBJs. Finally, we demonstrate room-temperature operation of the devices. The results obtained are compared with recent predictions by Xu [H. Q. Xu, Appl. Phys. Lett. 78, 2064 (2001)] and good agreement is found.

Room-temperature and 50 GHz operation of a functional nanomaterial

We demonstrate an artificial electronic nanomaterial, constructed by arrangement of nanometer-sized symmetry-breaking elements into a two-dimensional lattice. The material exhibits intrinsic nonlinear electronic functionality, and therefore functions also as a two-dimensional ratchet. We show that individual devices can be made by simply cutting pieces from the material. We also demonstrate that these devices operate at temperatures up to room temperature and at frequencies at least up to 50 GHz.

Operation of InGaAs/InP-Based Ballistic Rectifiers at Room Temperature and Frequencies up to 50 GHz

Novel semiconductor rectifiers based on ballistic electron transport are fabricated from a high electron-mobility InGaAs/InP wafer. Because the device sizes are sufficiently small, operations at room temperature are achieved. Furthermore, the devices are shown to work not only at least up to 50 GHz but also with a sensitivity roughly the same as commercial microwave diodes, despite the fact that the devices have not yet been optimized. Aspects of using the devices in microwave applications are discussed in terms of the physical mechanism of the novel rectifying effect.

Defects in porous silicon investigated by optically detected and by electron paramagnetic resonance techniques

The defect properties of as‐etched and annealed porous silicon are studied by electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR). The paramagnetic defect observed is closely related to the Pb0 center at the Si/SiO2 interface. In EPR a minimum defect density of 1016 cm−3 is observed for the as‐etched silicon, which reaches a maximum of 8×1018 cm−3 for samples annealed at about 400 °C. In the ODMR experiments, the same dangling bond center is observed on the 1.5 eV luminescence band enhancing the luminescence—but with increased sensitivity and as a decrease of the emission intensity in the infrared emission band at 1 eV of porous silicon.

Actomyosin motility on nanostructured surfaces

We have here, for the first time, used nanofabrication techniques to reproduce aspects of the ordered actomyosin arrangement in a muscle cell. The adsorption of functional heavy meromyosin (HMM) to five different resist polymers was first assessed. One group of resists (MRL-6000.1XP and ZEP-520) consistently exhibited high quality motility of actin filaments after incubation with HMM. A second group (PMMA-200, PMMA-950, and MRI-9030) generally gave low quality of motility with only few smoothly moving filaments. Based on these findings electron beam lithography was applied to a bi-layer resist system with PMMA-950 on top of MRL-6000.1XP. Grooves (100-200nm wide) in the PMMA layer were created to expose the MRL-6000.1XP surface for adsorption of HMM and guidance of actin filament motility. This guidance was quite efficient allowing no U-turns of the filaments and approximately 20 times higher density of moving filaments in the grooves than on the surrounding PMMA.

Ga0.25In0.75As/InP quantum wells with extremely high and anisotropic two‐dimensional electron gas mobilities

Measurements of modulation‐doped Ga0.25In0.75As/InP quantum wells show, in the 〈−110〉 direction, a record electron mobility of 520 000 cm2/V s at 300 mK. A mobility difference of 15% between the 〈110〉 direction and the 〈−110〉 direction is observed. This anisotropy is tentatively attributed to an ordering effect. The mobilities at room temperature and at 77 K were 16 100 and 170 000 cm2/V s, respectively. By separating out the ionized impurity scattering from other scattering processes in the quantum well, we conclude that at low electron concentrations ionized impurity scattering is limiting the mobility, while alloy scattering has a strong influence on the mobility at high electron concentrations. From this result we determine the first experimental value of the alloy‐scattering potential as ΔV=0.3 eV.

Electron spin resonance investigations of oxidized porous silicon

The defect properties of rapidly thermally oxidized porous silicon are studied by electron paramagnetic resonance. Two different types of defects can be distinguished. One is very similar to the defects observed in damaged crystalline or amorphous Si, whereas the second one is closely related to the Pb center. A maximum defect density of 8×1018 cm−3 is observed for samples annealed at about 600 °C. The intensity of the photoluminescence band at 1.7 eV anticorrelates with the density of the defects.

Guiding motor-propelled molecules with nanoscale precision through silanized bi-channel structures

Guiding motor-propelled molecules with nanoscale precision through silanized bi-channel structures