Investigation on deep level defects in rapid thermal annealed undoped n-type InP

Deep levels in rapid thermal annealed Pd/n-InP Schottky contacts have been studied using deep level transient spectroscopy. It is observed that the as-deposited Pd/n-InP Schottky sample exhibit two deep levels with activation energies of 0.53 and 0.70 eV. In samples annealed at 400 °C, three deep levels having activation energies 0.18, 0.30 and 0.86 eV below the conduction band are observed and for samples annealed at 500 °C, four deep levels with activation energies 0.33, 0.44, 0.70 and 0.82 eV are observed. Fourier transform infrared spectroscopy measurements have been carried out on undoped as-deposited and annealed InP wafers at 300, 400 and 500 °C. The measurements revealed high concentration of hydrogen complexes in the form of V_InH₄ existing in InP wafer. The results show that V_InH₄ complex annihilates with increase of annealing temperature and results in the formation of P _In ²⁺ and V _P ⁺ defects at 0.70 and 0.44 eV, respectively.     

Prediction of phonon thermal transport in thin GaAs, InAs and InP nanowires by molecular dynamics simulations: influence of the interatomic potential

A number of different potentials are currently being used in molecular dynamics simulations of semiconductor nanostructures. Confusion can arise if an inappropriate potential is used. To illustrate this point, we performed direct molecular dynamics simulations to predict the room temperature lattice thermal conductivity λ of thin GaAs, InAs and InP nanowires. In each case, simulations performed using the classical Harrison potential afforded values of λ about an order of magnitude smaller than those obtained using more elaborate potentials (an Abell-Tersoff, as parameterized by Hammerschmidt et al for GaAs and InAs, and a potential of Vashishta type for InP). These results will be a warning to those wishing to use computer simulations to orient the development of quasi-one-dimensional systems as heat sinks or thermoelectric devices.     

Probing the wurtzite conduction band structure using state filling in highly doped InP nanowires

We have grown InP nanowires doped with hydrogen sulfide, which exhibit sulfur concentrations of up to 1.4%. The highest doped nanowires show a pure wurtzite crystal structure, in contrast to bulk InP which has the zinc blende structure. The nanowires display photoluminescence which is strongly blue shifted compared with the band gap, well into the visible range. We find evidence of a second conduction band minimum at the gamma point about 0.23 eV above the band edge, in excellent agreement with recent theoretical predictions. Electrical measurements show high conductivity and breakdown currents of 10(7) A/cm(2).     

Anisotropies of the g-factor tensor and diamagnetic coefficient in crystal-phase quantum dots in InP nanowires

Nano Research - Crystal-phase low-dimensional structures offer great potential for the implementation of photonic devices of interest for quantum information processing. In this context, unveiling...     

Core-shell multi-quantum wells in ZnO/ZnMgO nanowires with high optical efficiency at room temperature

Nanowire-based light-emitting devices require multi-quantum well heterostructures with high room temperature optical efficiencies. We demonstrate that such efficiencies can be attained through the use of ZnO/Zn((1-x))Mg(x)O core-shell quantum well heterostructures grown by metal organic vapor phase epitaxy. Varying the barrier Mg concentration from x?=?0.15 to 0.3 leads to the formation of misfit induced dislocations in the multi-quantum wells. Correlatively, temperature dependent photoluminescence reveals that the radial well luminescence intensity decreases much less rapidly with increasing temperature for the lower Mg concentration. Indeed, about 54% of the 10?K intensity is retained at room temperature with x?=?0.15, against 1% with x?=?0.30. These results open the way to the realization of high optical efficiency nanowire-based light-emitting diodes.     

Large-energy-shift photon upconversion in degenerately doped InP nanowires by direct excitation into the electron gas

Realizing photon upconversion in nanostructures is important for many next- generation applications such as biological labelling, infrared detectors and solar cells. In particular nanowires are attractive for optoelectronics because they can easily be electrically contacted. Here we demonstrate photon upconversion with a large energy shift in highly n-doped InP nanowires. Crucially, the mechanism responsible for the upconversion in our system does not rely on multi-photon absorption via intermediate states, thus eliminating the need for high photon fluxes to achieve upconversion. The demonstrated upconversion paves the way for utilizing nanowires--with their inherent flexibility such as electrical contactability and the ability to position individual nanowires--for photon upconversion devices also at low photon fluxes, possibly down to the single photon level in optimised structures.     

Resolution limit due to thermal effects in low-temperature scanning electron microscopy

By scanning a thin-film superconductor with the electron beam in a scanning electron microscope equipped with a low-temperature stage, a two-dimensional voltage image of spatial structures in the sample configuration can be generated. The spatial resolution of this technique has been investigated by monitoring the voltage response of a current-biased superconducting microbridge as a function of the distance between the microbridge and the point of the electron-beam focus. The results indicate that the electron irradiation can be treated as a local heating effect and that the spatial resolution is dominated by the thermal healing length. By modulating the beam at high frequencies, one can reduce the thermal healing length considerably below its low-frequency limit because of the thermal skin effect. It appears that, depending upon the sample parameters, a spatial resolution limit of less than1 µm can be obtained.     

气态膜过程中的热效应

实验表明提高温度（Ｔ）能大幅度增加挥发性物质在气态膜过程中的传质系数（Ｋ），Ｋ和Ｔ间的关系符合Ａｒｒｈｅｎｉｕｓ方程Ｋ＝Ｋｏｅｘｐ（－Ｅ／ＲＴ）。用Ｓｔｏｋｅｓ－Ｅｉｎｔｅｉｎｓ和Ｌｅｖｅｑｅ方程，从理论上证实：（１）对于易挥发性物质（如ＨＣＮ），温度主要是通过降低进水边界层中水溶液的粘度或提高扩散系数，而使传质系数大幅度升高；（２）对于挥发性较小的物质（如苯酚），温度主要是通过提高其蒸汽压或进水     

Non fermi liquid behavior in semimetals. Applications to the fullerenes

In a variety of semimetals with vanishing density of states the Fermi level, the low energy electronic states are described by an effective Dirac equation, instead, of the more conventional effective mass approximation (equivalent to Schrodinger equation). When this happens, electron-electron interactions give rise to anomalous features, which differ from those of conventional metals and insulators. A comprehensive discussion of these effects is presented, making use of the fact that Dirac electrons interacting through Coulomb forces lead to a well defined, renormalizable, quantum field theory, which has many similarities to quantum electrodynamics. The most remarkable feature is the absence of a coherent quasiparticle pole, like in 1D Luttinger liquids.     

Using quantum interferometers to make measurements at the Heisenberg limit

In recent work we proposed a quantum interferometer and showed how it could be used to significantly enhance the resolution that could be achieved in measurement schemes. In this paper, we outline a detailed scheme on how these quantum interferometers could be implemented. We also analyze the effects of dissipation and of imperfect detectors and show that this scheme is remarkably robust to both. This suggests that quantum interferometers may provide a promising route for implementing sub-shot-noise limited measurements in the laboratory.     

Practical low dose limits for passive personal dosemeters and the implications for uncertainties close to the limit of detection

Recent years have seen the increasing use of passive dosemeters that have high sensitivities and, in laboratory conditions, detection limits of <10 μSv. However, in real operational use the detection limits will be markedly higher, because a large fraction of the accrued dose will be due to natural background, and this must be subtracted in order to obtain the desired occupational dose. No matter how well known the natural background is, the measurement uncertainty on doses of a few tens of microsieverts will be large. Individual monitoring services need to recognise this and manage the expectations of their clients by providing sufficient information.     

Measurement of refractive-index change at a liquid-solid interface close to the critical angle

We measured the refractive-index change on a liquid sample, using the reflection of a polarized Gaussian laser beam close to the angle of total reflection. We applied this technique to a solution of nickel (ii) phthalocyanine tetrasulfonated (NiPTS) in water-ethanol (1/1 v/v), in which the nonlinearity of the refractive index is due to optically induced thermal effects. We show that close to the angle of total reflection the sensitivity of this technique is four times bigger than at normal incidence.     

On the strength of a body at temperatures close to its melting point

On the example of frozen soils and ice existing at temperatures close to the melting point, the existence of two mechanisms (types) of destruction related to the phase transitions of water is shown. The first mechanism that operates near the melting point is plastic destruction, it gradually converts an ice body into a liquid-like state. The second mechanism operating far from the melting point is brittle destruction, disintegration into parts, with a slight preliminary deformation. For both types of destruction equations of long-term strength and of the behavior of deformation in time have been obtained.     

Statistical analysis of excitonic transitions in single,free-standing GaN nanowires: Probing impurity incorporation in the poissonian limit

Single, free-standing GaN nanowires grown by plasma-assisted molecular-beam epitaxy have been investigated with low temperature micro-photoluminescence. The quantitative analysis of the luminescence spectra of around 100 nanowires revealed that each nanowire exhibits its own individual spectrum. A significant fraction of nanowires exclusively emits at energies corresponding to either surface-donor-bound or free excitons, demonstrating that optical properties of individual nanowires are determined by a few impurity atoms alone. The number of impurities per nanowire and their location within the nanowires varies according to Poissonian statistics.     

The viscosity and thermal conductivity of ethane in the limit of zero density

New representations of the viscosity and thermal conductivity of ethane in the limit of zero density are provided. The correlation for the viscosity extends over the temperature range 200 to 1000 K, whereas that for thermal conductivity extends from 225 to 725 K. The behavior of each property is represented by an independent correlation of the appropriate effective collision cross section as a function of temperature. The final results are compared with experimental data as well as with earlier correlations. The accuracy of the viscosity correlation is estimated to be ±0.5 % in the temperature range 300 KT600 K, increasing to ±1.5 and ±2.5% at 200 and 1000 K, respectively. The uncertainty associated with the thermal conductivity correlation is ±2 % in the temperature range 300 KT500 K, increasing to ±3% at either end. The results of this study indicate that there is an urgent need for additional high-precision measurements of thermal conductivity especially for temperatures above 400 K.     

Modeling the delay in mixing to the molecular level in calculating the thermal radiation of turbulent flows

An appropriate method is proposed for taking account of the delay in mixing to the molecular level in turbulent flows of jet type; the method is intended for the calculation of the thermal radiation.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 46, No. 2, pp. 225–233, February, 1984.     

Normalized parameter relating the spherical aberration of a thin lens to the diffraction limit and fiber coupling efficiency

In this paper, we calculate the transverse spherical aberration TA of a thin lens and defines a normalized aberration Y equal to TA divided by the theoretical resolution limit. As a rule of thumb, (a) a thin lens that suffers only from spherical aberration may be considered effectively diffraction-limited as long as Y < 1.6. Similarly, (b) the coupling efficiency of a Gaussian beam to a single-mode fiber may be high even when Y > 1.6, and, specifically, (c) the lens need be diffraction-limited only over a radius approximately equal to the radius (to the 1/e-point) of the Gaussian beam.