Electron/Hole Transport in III-V One-Dimensional Nanostructures - Quantum Wires

One-dimensional nanostructures have attracted much attention due to their unique electronic properties and their potential for device applications including field-effect transistors, magnetic sensors, infra-red photodetectors, lasers, and thermoelectric elements. We grow self-organized nanowires using solid-source molecular beam epitaxy to study electron transport in these nanostructures. Previously much attention has been devoted to their optical and structural properties, however little experimental work on the electron/hole transport in these nanostructures has been done. To understand the theoretically predicted transport and the underlying physics in this class of materials we are studying the temperature dependent Hall effect, magnetoresistance (Shubnikov-de-Haas experiments), quantum Hall effect, and capacitance-voltage characteristics. Primarily, we focus on the electron scattering phenomena which determine conductivity, lateral coupling between nanowires through tunneling and hopping, weak localization and electron-electron scattering, anti-weak localization effects and spin-orbit coupling in one-dimensional self-organized nanostructures.

Applied Physics Letters 97, 262103 (2010)

Electron Transport in III-V Hybrid One-Dimensional Nanostructures - Quantum Dot Chains

Separately quantum dots and quantum wires were studied optically and structurally by many groups. Hybrid structures such as quantum dot-chains confined in two dimensions (1D wetting layer) and all three dimensions (aligned and coupled 0D quantum dots) were recently grown in our MBE laboratory providing a unique opportunity to explore the physics of this class of nanostructures. Currently, we focus on electronic properties by probing quantum dot chain nanostructures optically and electrically. In particular, we are interested in electron self-interference phenomena at low temperatures (weak localization), dot-to-dot electron hopping, tunneling, electron-phonon interaction, etc. We believe that these materials are promising for optoelectronic and thermoelectric device applications.

Fluctuations Studies in Heterostructures with Reduced Dimensionality

Low frequency noise in semiconductors is a result of fluctuations in conductivity which can be caused by fluctuations in the number of carriers or in the mobility fluctuations of those carriers. Even for bulk materials there is an open discussion about which phenomena dominates low frequency noise. For heterosructures, where charge is confined in one, two, or three dimensions, the electronic properties of these structures differ from bulk materials. The question is how the electron/hole confinement will affect low frequency fluctuations of conductivity? Answering this question will shed more light on advantages and drawbacks of these materials for device applications. Additionally, we use low frequency noise measurements to probe material quality, study defects in semiconductors, and to characterize defects in terms of activation energies, capture cross sections, spatial location, and densities. Furthermore, the low-frequency noise measurements let us estimate the signal to noise ratio of a variety of devices and determine their lower measurement thresholds. For example, by knowing the signal-to-noise ratio of a Hall effect magnetometer one can establish the lowest magnetic field the device is capable of detecting.

Journal of Applied Physics 104, 103709 (2008)

Development of Highly Sensitive, Low Noise Micro-Hall Sensors

Micro-Hall effect sensors, which are widely used in industry and research applications, have recently been considered for bio-medical investigations as they possess important characteristics for bio applications: high spatial resolution, high sensitivity, and operate at room temperature. We focus on growth, fabrication, and characterization of these devices using high electron drift velocity semiconductors such as InAs, InSb and InGaAs. The main goal of this research is the improvement of magnetometer sensitivity, the reduction of low-frequency noise, and optimization of sensor thermal drift. Most of these devices are built of InSb, InGaAs, or InAs quantum wells doped remotely or directly in the conductive channel.

Development of New Generation of Photovoltaic Devices