Nanoscale Semiconductor Structures Research Articles

INFLUENCE О F А STR О NG M А GNETIC FIELD О N FERMI ENERGY О SCILL А TI О NS IN TW О -DIMENSI О N А L SEMIC О NDUCT О R M А TERI А LS

This article shows that the Fermi levels of a nanoscale semiconductor in a quantizing magnetic field are quantized. A method is proposed for calculating the Fermi energy oscillations for a two-dimensional electron gas at different magnetic fields and temperatures. An analytical expression is obtained for calculating the Fermi-Dira c distribution function at high temperatures and weak magnetic fields. With the help of the propos ed formula, the experimental results in nanoscale semiconductor structures are investigated. Using fo rmula, Fermi energy oscillations are explained for two-dimensional electron gases in quantum wells (quantum wells, mainly GaAs/GaAlAs heterostructures) with a parabolic dispersion law. Keywоrds:quаntizing mа gnetic field, temperаture, Fermi energy, n аnоscаle semicоnductоrs,twо-dimensiоnаl structures, dispersiоn.

DETERMINATION OF THE TEMPERATURE DE PENDENCE OF THE FERMI ENERGY OSCILLATIONS IN NANOSTRUCTURED SE MICONDUCTOR MATERIALS IN THE PRESENCE OF A QUANTIZING MAGNETIC FIELD

In this article investigated the effects of a quantizing magnetic field and temperature on Fermi energy oscillations in nanoscale semiconducto r materials. It is shown that the Fermi energy of a nanoscale semiconductor material in a quantizing magnetic field is quantized. For the first time, a mathematical model was developed for determining the effect of temperature and a quantizing magnetic field on oscillations of the Fermi energy in nanoscale semiconductor structures with a parabolic dispersion law

МОДЕЛИРОВАНИЕ ТЕМПЕРАТУРНОЙ ЗАВИСИМОСТИ КВАНТОВЫХ ОСЦИЛЯЦИОННЫХ ЭФФЕКТОВ В 2D ПОЛУПРОВОДНИКОВЫХ МАТЕРИАЛАХ

For the first time, a mathematical model was developed for determining the effect o f temperature and a quantizing magnetic field on oscillations o f the Fermi energy in nanoscale semiconductor structures with a parabolic dispersion law. A mathematical expression is derived for calculating the dependence o f the distribution o f the Fermi-Dirac function on the magnetic field, on the thickness o f the quantum well and on the temperature in low-dimensional semiconductor materials. The possibility o f calculating the Fermi energy oscillations in two-dimensional electron gases at high temperatures and weak magnetic fields is shown for the first time. The proposed theory explains the experimental results in two-dimensional semiconductor structures with a parabolic dispersion law.

Highly Directional Deposition of Oriented Nanoscale Semiconductor Structures with Phototropic Control

Semiconducting chalcogen films consisting of high-fidelity, periodic nanoscale elements displaying significant structural anistotropy were deposited using a light-guided electroplating technique without any lithographic processing. The direction of the material growth with respect to the substrate was controlled by manipulating the light propagation vector. Thus, the morphological determination of the structures was guided in the same manner as the growth of sunflowers and palm trees are guided by the sun, natural phototropism. Additional morphological complexity was generated by combining the use of inclined illumination with a series of defined polarization and wavelength inputs which allowed variation of the feature anisotropy, in-plane and out-of-plane orientation, spacing, and periodicity. The optical control of the morphological determination was a consequence of light scattering and a spontaneous optimization of the interfacial light absorption during deposition. These fundamental processes were simulated using a finite-difference time domain method to model the light-matter interactions and a Monte Carlo method for mass addition. The results of the simulation successfully reproduced the experimentally observed morphologies, affirming that the light response was a fully optically-induced phenomenon. The underlying optical basis was further investigated using a simplified light scattering model that corroborated the magnitude and direction of the empirically-observed phototropic responses.

Growth and characterization of grid-like β-Ga2O3 nanowires by electric field assisted chemical vapor deposition method

Gallium oxide (Ga2O3) has five crystalline polymorphs, i.e. corundum (α-phase), monoclinic (β-phase), spinel (γ-phase), bixbite (δ-phase) and orthorhombic (ε-phase). Among these phases, the monoclinic structured β-Ga2O3 is the most stable form, and is a ultraviolet (UV) transparent semiconductor with a wide band gap of 4.9 eV. It is a promising candidate for applications in UV transparent electrodes, solar-blind photodetectors, gas sensors and optoelectronic devices. In recent years, one-dimensional (1D) nanoscale semiconductor structures, such as nanowires, nanobelts, and nanorods, have attracted considerable attention due to their interesting fundamental properties and potential applications in nanoscale opto-electronic devices.Numerous efforts have been made to fabricate such devices in 1D nanostructures such as nanowires and nanorods. Comparing with the thin film form, the device performance in the 1D form is significantly enhanced as the surface-to-volume ratio increases. In order to realize β-Ga2O3 based nano-optoelectronic devices, it is necessary to obtain controlled-synthesis and the high-quality β-Ga2O3 nanomaterials. According to the present difficulties in synthesizing β-Ga2O3 nanomaterials, in this paper, the grid-like β-Ga2O3 nanowires are prepared on sapphire substrates via electric field assisted chemical vapor deposition method.High-purity metallic Ga (99.99%) is used as Ga vapor source. High-purity Ar gas is used as carrier gas. The flow rate of high-purity Ar carrier gas is controlled at 200 sccm. Then, oxygen reactant gas with a flow rate of 2 sccm enters into the system. The temperature is kept at 900℃ for 20 min. The effect of the external electric voltage on the surface morphology, crystal structure and optical properties of β-Ga2O3 nanowires are investigated. It is found that the external electric voltage has a great influence on the surface morphology of the sample. The orientation of the β-Ga2O3 nanowires grown under the action of an applied electric field begins to improve. Only a grid composed of three different growth directions appears. And with the increase of applied voltage, the distribution of nanowires becomes denser and the length increases significantly. In addition, it is found that the chemical vapor deposition method assisted by this external electric field can significantly improve the crystallization and optical quality of the samples.

Enhanced light–matter interaction at nanoscale by utilizing high-aspect-ratio metallic gratings

We report the design, fabrication, and experimental characterization of high-aspect-ratio metallic gratings integrated with nanoscale semiconductor structures, which enable efficient light-matter interaction at the nanoscale over interaction lengths as long as two times of the effective optical wavelength. The efficient light-matter interaction at the nanoscale is enabled by excitation of the guided modes of subwavelength slab waveguides formed by the high-aspect-ratio metallic gratings. By controlling the height of the high-aspect-ratio gratings, the wavelength of the guided modes through the nanoscale semiconductor structures is determined.

Conditional statistics of electron transport in interacting nanoscale conductors

Interactions between nanoscale semiconductor structures form the basis for charge detectors in the solid state. Recent experimental advances have demonstrated the on-chip detection of single electron transport through a quantum dot (QD). The discreteness of charge in units of e leads to intrinsic fluctuations in the electrical current, known as shot noise. To measure these single-electron fluctuations a nearby coherent conductor, called a quantum point contact (QPC), interacts with the QD and acts as a detector. An important property of the QPC charge detector is noninvasiveness: the system physically affects the detector, not visa-versa. Here we predict that even for ideal noninvasive detectors such as the QPC, when a particular detector result is observed, the system suffers an informational backaction, radically altering the statistics of transport through the QD as compared to the unconditional shot noise. We develop a theoretical model to make predictions about the joint current probability distributions and conditional transport statistics. The experimental findings reported here demonstrate the reality of informational backaction in nanoscale systems as well as a variety of new effects, such as conditional noise enhancement, which are in essentially perfect agreement with our model calculations. This type of switching telegraph process occurs abundantly in nature, indicating that these results are applicable to a wide variety of systems.

Quasi-ballistic electron transport in nanoscale semiconductor structures

Quasi-ballistic electron transport in nanoscale semiconductor structures

Inclusion of Nonlinear Strain Effects in the Hamiltonian for Nanoscale Semiconductor Structures

Inclusion of Nonlinear Strain Effects in the Hamiltonian for Nanoscale Semiconductor Structures

Optical phonon instability induced by high-speed electron transport in nanoscale semiconductor structures

We analyze the interaction of high-speed electrons and polar optical phonons in nanoscale semiconductor structures. Under the velocity overshoot regime, it is found that electrons can induce optical phonon instability (i.e., the lattice optical vibrations grow in time when the electric current exceeds a threshold value). For nanoscale diodes based on III-V compounds, the threshold current density is estimated to be of the order of $100\phantom{\rule{0.3em}{0ex}}\mathrm{kA}∕{\mathrm{cm}}^{2}$ and the corresponding bias $0.5--1.5\phantom{\rule{0.3em}{0ex}}\mathrm{V}$ for the diode lengths of $50--100\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The wavelengths of unstable phonons are about $10\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ with the characteristic time for instability development in the $10\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ range. We suggest that this phenomenon can lead to efficient generation of coherent optical phonons with a number of potential applications.

Kinetics of Quasiballistic Transport in Nanoscale Semiconductor Structures: Is the Ballistic Limit Attainable at Room Temperature?

Electron transport in nanoscale semiconductor structures is theoretically investigated to answer the question of whether or not the ballistic limit is really attainable under room temperature operation. The semiclassical Boltzmann transport equation is solved analytically under the relaxation time approximation for n(+)-n-n(+) test structures. We demonstrate that the solution of the Boltzmann transport equation exhibits a boundary layer structure near the potential barrier and thus the scatterings in the active region cannot be neglected even in nanoscale structures, as far as they are operated at room temperature under high applied voltages.

Kinetic study of velocity distributions in nanoscale semiconductor devices under room-temperature operation

Quasiballistic electron transport in nanoscale semiconductor structures is investigated to clarify the importance of scatterings under room-temperature operation as reflected in the velocity distribution functions. The analyses are carried out for n+-n-n+ structures based on the semiclassical Boltzmann transport equation (BTE). It is shown that the number of electrons with negative velocity grows exponetially due to scatterings around the top of the electronic potential barrier in the channel region and, thus, the scatterings cannot be neglected even in nanoscale device structures. This is closely related to the mathematical structure of the BTE whose solution exhibits the boundary-layer structure.

The contribution of the amorphous phase in nanocrystalline thin films of germanium and gallium arsenide

AbstractThe nanoscale semiconductor structures obtained by evaporation in high vacuum at different temperatures show anomalous high photoconductivity. This may be connected with the structure of clusters which can consist of both crystalline and amorphous phases. We propose a method of extracting amorphous and crystalline contributions to the clusters. This method is based on the extraction of corresponding contributions to the extended x‐ray absorption fine structure (EXAFS) spectra. The method of EXAFS spectroscopy allows information to be obtained about the local atomic structure of materials in different states, including gases and liquids. The macro‐structure of films was examined by different methods, i.e. x‐ray diffraction, transmission electron microscopy (TEM), and atomic force microscopy (AFM). We obtained the volume portion of the amorphous phase to the nanosized particles of Ge as about 70% and for GaAs about 50%. Copyright © 2004 John Wiley & Sons, Ltd.

Dopant atom clustering and charge screening induced roughness of electronic interfaces in GaAsp-nmultilayers

The roughness of the electronic interfaces of p-n GaAs multilayers is investigated by cross-sectional scanning tunneling microscopy. Two physically different contributions to the roughness are found, both much larger than the underlying atomically sharp ``metallurgical'' interface. The roughness arises from the individual electrostatic screening fields around each dopant atom near the interface and from a clustering of dopant atoms. The latter leads to charge-carrier-depleted zones extending locally through the entire nominally homogeneously doped layer for layer thicknesses close to the cluster dimension, hence limiting the precision of the spatial and energetic positioning of the Fermi energy in nanoscale semiconductor structures.

Roughness of electronic interfaces in Ga As p-n multilayers investigated by cross-sectional scanning tunneling microscopy

AbstractWe investigated the roughness of the electronic interfaces of GaAs p-n multilayers using cross-sectional scanning tunneling microscopy. We demonstrate that these interfaces exhibit a much larger roughness than the underlying essentially perfect ‘metallurgical’ interface, due to the individual long range electrostatic screening fields around each dopant atom near the interface and due to a clustering of dopant atoms. The clustering and the inherently connected local lack of dopant atoms gives rise to charge carrier depletion zones extending locally through entire nominally homogeneously doped layers once the layer thickness is close to the cluster dimensions. Thus, local variations in the dopant atom distribution limit the precision of the spatial and energetic positioning of the Fermi energy in nanoscale semiconductor structures.

Tailoring of optical phonon modes in nanoscale semiconductor structures: role of interface-optical phonons in quantum-well lasers

This paper discusses the concept of enhancing semiconductor laser performance through tailoring of scattering rates of confined polar-optical phonons. Studies of optically pumped intersubband scattering in coupled quantum-well lasers have demonstrated that interface-phonon-assisted transitions are important in such structures; furthermore, simple analytical expressions have been derived that indicate the importance of interface-phonon scattering in quantum-well lasers. These calculations reveal that the interface-phonon-assisted transitions are dominant for small quantum well dimensions of approximately 40 Å; such dimensions are typical of novel lasers including both the unipolar quantum cascade laser and the tunneling injection laser. Recent numerical calculations have confirmed these effects and have extended them to indicate how confined and interface phonons also affect critical laser properties such as optical gain. The application of confined phonon effects to intersubband lasers is one of the most important applications of confined-phonon physics to the present time.