Hole capture barrier of self-organized InAs quantum dots

Deep level transient spectroscopy (DLTS) technique was successfully applied to characterize the electric properties of p type self-organized InAs quantum dots. The ground state energy and capture barrier energy of hole of quantum dots were measured for the first time. The energy of ground state of 2.5ML InAs quantum dots with respect to the valence band of bulk GaAs was obtained being about 0.09eV, and there was a barrier associated to the change of charge state of quantum dots. The capture barrier energy of such dots for hole was about 0.26eV. The work is very meaningful for further understanding the intrinsic properties of quantum dots.

Temperature-induced turnover of the well and barrier layers in ZnSe/Zn0.84Mn0.16Se superlattices

Photoluminescence of ZnSe, Zn0.84Mn0.16Se alloy, and ZnSe/Zn0.84Mn0.16Se superlattice (SL) have been measured in the temperature range from 10 to 300 K. It is found that the band gap of the ZnSe was smaller than that of the Zn0.84Mn0.16Se alloy at 10 K, but larger than that of the alloy at 300 K. Then the well and barrier layers of the ZnSe/Zn0.84Mn0.16Se SL would be expected to turn over at about 180 K. This type of turn over was observed in the SL sample. The turn over took place at 80 K, somewhat lower than the expected temperature. A calculation including the strain in the ZnSe/Zn0.84Mn0.16Se SL indicates that the heavy-hole bands begin crossing at 75 K, which agrees well with experimental results. [S0163-1829(99)13127-8].

Structural and photoelectric studies on double barrier quantum well infrared detectors

GaAs/AlAs/GaAlAs double barrier quantum well (DBQW) structures are employed for making 3-5 um photovoltaic infrared (IR) detectors with a peak detectivity of 5 x 10(11) cm Hz(1/2)/W at 80 K. Double crystal X-ray diffraction is combined with synchrotron radiation X-ray analysis to determine successfully the exact thickness of GaAs, AlAs and GaAlAs sublayers. The interband photovoltaic (PV) spectra of the linear array of the detectors are measured directly by edge excitation method, providing the information about spatial separation processes of photogenerated carriers in the multiquantum wells and the distribution of built-in field in the active region. The spectral response of the IR photocurrent of the devices is also measured and compared with the temperature dependent IR absorption of the DBQW samples in order to get a better understanding of the bias-controlled optical and transport behavior of the detector photoresponse and thus to optimize the detector performance. (C) 1999 Elsevier Science Ltd. All rights reserved.

Transport property in narrow barrier GaAs/AlAs superlattice under hydrostatic pressure

The current-voltage (I-V) characteristics of a doped weakly coupled GaAs/AlAs superlattice (SL) with narrow barriers are measured under hydrostatic pressure from 1 bar to 13.5 kbar at both 77 and 300 K. The experimental results show that, contrary to the results in SL with wide barriers, the plateau in the I-V curve at 77 K does not shrink with increasing pressure, and becomes wider after 10.5 kbar. It is explained by the fact that the E-Gamma 1-E-Gamma 1 resonance peak is higher than the E-Gamma 1-E-X1 resonance peak. At 300 K, however, because of the more important contribution of the nonresonant component to the current, the plateau shrinks with increasing pressure. (C) 1999 American Institute of Physics. [S0021-8979(99)02008-3].

Suppression of sequential tunneling current by a perpendicular magnetic field in a three-barrier, two-well heterostructure

When an intersubband relaxation is involved in vertical transport in a tunneling heterostructure, the magnetic suppression of the intersubband LO or LA phonon scattering may also give rise to a noticeable depression of the resonant tunneling current, unrelated to the Coulomb correlation effect. The slowdown of the intersubband scattering rate makes fewer electrons able to tunnel resonantly between two adjacent quantum wells (QWs) in a three-barrier, two-well heterostructure. The influence of the magnetic field on the intersubband relaxation can be studied in an explicit way by a physical model based on the dynamics of carrier populations in the ground and excited subbands of the incident QW. (C) 1998 American Institute of Physics. [S0003-6951(98)00925-5].

Oscillatory magneto-conductance in quantum waveguides with lateral multi-barrier structures

The magneto-transport properties of a narrow quantum waveguide with lateral multibarrier modulation are investigated theoretically. It is found that the magnetoconductance as a function of Fermi energy or magnetic field exhibits square-wave-like oscillations. In the presence of magnetic field, the edge states are formed near each barrier and the boundaries. Therefore, the number of edge states increases with the number of lateral barriers, leading to the increase of the propagating modes. On the other hand, owing to the tunneling effect a pair of edge states around the barrier region with opposite moving directions may be coupled and formed a circulating localized state, leading to the quenching of the related propagating states. The resulting dispersion relation exhibits oscillation structures superimposed on the bulk Landau levels. These novel conductance characteristics may provide potential applications to the fabrication of new quantum devices.

Energy spectrum and persistent currents in finite-width mesoscopic ring with radial potential barrier threading a magnetic flux through its hole

The energy spectrum and the persistent currents are calculated for a finite-width mesoscopic annulus with radial potential barrier, threading a magnetic flux through the hole of the ring. Owing to the presence of tunneling barrier, the coupling effect leads to the splitting of each radial energy subband of individual concentrical rings into two one. Thus, total currents and currents carried by single high-lying eigenstate as a function of magnetic flux exhibit complicated patterns. However, periodicity and antisymmetry of current curves in the flux still preserve.

Tunneling transmission in two quantum wires coupled by a magnetically defined barrier

A numerical analysis of an electron waveguide coupler based on two quantum wires coupled by a magnetically defined barrier is presented with the use of the scattering-matrix method. For different geometry parameters and magnetic fields, tunneling transmission spectrum is obtained as a function of the electron energy. Different from that of conventional electron waveguide couplers, the transmission spectrum of the magnetically coupled quantum wires does not have the symmetry with regard to those geometrically symmetrical ports, It was found that the magnetic field in the coupling region drastically enhances the coupling between the two quantum wires for one specific input port while it weakens the coupling for the other input port. The results can be well understood by the formation of the edge states in the magnetically defined barrier region. Thus, whether these edge states couple or decouple to the electronic propagation modes in the two quantum wires, strongly depend on the relative moving directions of electrons in the propagating mode in the input port and the edge states in the magnetic region. This leads to a big difference in transmission coefficients between two quantum wires when injecting electrons via different input ports. Two important coupler specifications, the directivity and uniformity, are calculated which show that the system we considered behaves as a good quantum directional coupler. (C) 1997 American Institute of Physics.

Color filter-less technology of LED back light for LCD-TV - art. no. 68410G

Back Light Unit (BLU) and Color Filter are the two key components for the perfect color display of Liquid Crystal Display (LCD) device. LCD can not light actively itself, so a form of illumination, Back Light Unit is needed for its display. The color filter which consists of RGB primary colors, is used to generate three basic colors for LCD display. Traditional CCFL back light source has several disadvantages, while LED back light technology makes LCD obtain quite higher display quality than the CCFL back light. LCD device based on LED back light owns promoted efficiency of display. Moreover it can generate color gamut above 100% of the NTSC specification. Especially, we put forward an idea of Color Filter-Less technology that we design a film which is patterned of red and green emitting phosphors, then make it be excited by a blue light LED panel we fabricate, for its special emitting mechanism, this film can emit RGB basic color, therefore replace the color filter of LCD device. This frame typically benefits for lighting uniformity and provide pretty high light utilization ratio. Also simplifies back light structure thus cut down the expenses.

A New Technique for Side Pumping of Double-Clad Fiber Lasers

We report a new technique, called SAP, for side pumping of double-clad, rare-earth-doped fiber lasers using fiber-coupled pump sources. The highest coupling efficiency can even exceed 92% in theory with this structure.

Resonance-enhanced group delay times in an asymmetric single quantum barrier

It is shown that transmission and reflection group delay times in an asymmetric single quantum barrier are greatly enhanced by the transmission resonance when the energy of incident particles is larger than the height of the barrier. The resonant transmission group delay is of the order of the quasibound state lifetime in the barrier region. The reflection group delay can be either positive or negative, depending on the relative height of the potential energies on the two sides of the barrier. Its magnitude is much larger than the quasibound state lifetime. These predictions have been observed in microwave experiments. (c) 2005 Elsevier B.V. All rights reserved.

Kinetics of photoinduced anisotropy in bacteriorhodopsin film under two pumping beams

Photoinduced anisotropy in bacteriorhodopsin (BR) film arises from the selective bleaching of BR molecules to linearly polarized light. The kinetics of photoinduced anisotropy excited by single and two pumping beams are investigated theoretically and experimentally. Compared with a single pumping beam (650 nm), which produces comparatively small photoinduced anisotropy, dual-wavelength linearly polarized pumping beams (650 and 405 nm) can obviously change the photoinduced anisotropy. When the polarization orientation of the 405 ran pumping beam is perpendicular to that of the 650 nm pumping beam, the peak and steady values of the photoinduced anisotropy kinetic curves are remarkably enhanced. But when the two pumping beams have parallel polarization orientation, the peak and steady values are restrained. At a fixed intensity of the 650 nm pumping beam, there exists an optimal intensity for the 405 nm pumping beam to maximize the value of the photoinduced anisotropy. The photoinduced transmittance of the polarizer-BR-analyzer system is modulated by the polarization angle of the 405 nm pumping beam in an approximate-cosine form. (C) 2008 Optical Society of America.

Magnetic barrier on strained graphene: A possible valley filter

We put forward a two-terminal valley filter based on a bulk graphene sheet under the modulations of both a local perpendicular magnetic field and a substrate strain. When only one of the two modulations is present, no valley polarization can be generated. A combination of the two modulations leads to a different (but not opposite) shifts of the K and K' valleys, which could be utilized to generate a valley-polarized current. The degree of the valley polarization can be tuned by the strain strength and the inclusion of a scalar potential. The valley polarization changes its polarity as the local magnetic field switches its direction.

DENSITY-OF-STATES OF THE 2-DIMENSIONAL ELECTRON-GAS STUDIED BY MAGNETOCAPACITANCES OF BIASED DOUBLE-BARRIER STRUCTURES

The magnetocapacitive response of a double-barrier structure (DBS), biased beyond resonances, has been employed to determine the density of states (DOS) of the two-dimensional electron gas residing in the accumulation layer on the incident side of the DBS. An adequate procedure is developed to compare the model calculation of the magnetocapacitance with the experimental C vs B curves measured at different temperatures and biases. The results show that the fitting is not only self-consistent but also remarkably good even in well-defined quantum Hall regimes. As a result, information about the DOS in strong magnetic fields could reliably be extracted.