摘要:

We have studied the luminescence properties of microcavities which are formed by a single layer of poly(para‐phenylenevinylene) sandwiched between a dielectric mirror coated with a conducting indium tin oxide layer and a semitransparent metal electrode. Compared with a device without cavity structure, the spectral and spatial emission are significantly narrowed, and the forward emission intensity is enhanced. We measure a spectral linewidth (full width at half maximum) of the cavity modes of about 4 nm in photoluminescence and 20 nm in electroluminescence and an enhancement of luminescence intensity in the forward direction of more than an order of magnitude. The implications of the narrowing of the emission and possible transfer mechanisms for excitation energy are discussed. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362806

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An extended photoluminescence (PL) study of porous silicon is presented. Different PL techniques have been used: continuous wave excited (cw) PL, selectively excited PL, excitation spectroscopy of the PL, time decay of the PL, and time resolved PL. These measurements have been performed on a set of samples of various porosities and at various temperatures. Strong experimental evidence is found for the influence of disorder and of dispersive motion of excitons on the recombination dynamics. The data are interpreted in the framework of the trap‐controlled hopping mechanism for the dispersive motion of excitons in a disordered array of Si nanocrystals. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362807

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present an approach to the simulation of ultrasmall semiconductor devices based on Brownian motion of the carriers described by the Langevin equation. It follows the trajectories of individual particles in real space but does not require the computational effort of a full Monte Carlo simulation. This method is particularly useful for modeling very small devices where individual impurities and carriers must be considered, and the dynamics need to be treated atomistically, in a full‐scale three‐dimensional simulation. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362808

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Films of Sn oxide and oxyfluoride were made by reactive rf magnetron sputtering onto ITO‐coated glass. We analyzed the composition by Rutherford backscattering spectrometry, the structure by x‐ray diffraction, and the surface topography by atomic force microscopy. Li intercalation from a liquid electrolyte was more facile in the oxide than in the oxyfluoride, as found from cyclic voltammetry. Impedance spectra were taken for a wide range of frequencies and polarizing voltages. Nyqvist diagrams were interpreted from a circuit model with elements representing Li insertion at the electrolyte/film interface and electron insertion at the film/ITO interface. The data were consistent with a fractal surface of the Sn oxide film, with a dimension in excellent agreement with measures obtained through several independent techniques. The chemical diffusion coefficient was ∼10−13cm2/s and slightly decreasing with increasing potential for all films. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362809

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Carrier transport properties of (ZnS)3(ZnSe)42ordered and ZnS0.07Se0.93disordered alloys are studied. Iodine‐doped ZnS0.07Se0.93was grown by hydrogen radical‐enhanced chemical vapor deposition at a low temperature of 200 °C. These iodine‐doped ZnS0.07Se0.93are characterized by sharp x‐ray diffraction peaks and dominant blue band‐edge emissions in photoluminescence spectra. It was found that (ZnS)3(ZnSe)42ordered alloys show higher electron mobility over 100 cm2/V s than that of ZnS0.07Se0.93disordered alloys at a low electron concentration of ∼1016cm−3, even though these crystals have the same sulfur composition and crystallinity. This mobility enhancement in the ordered alloys is attributed to the elimination of ‘‘disorder scattering’’ originated from random atomic fluctuations in the disordered alloys. Carrier scattering mechanisms and donor activation processes in the ordered and disordered alloys were further determined by a temperature dependence of Hall measurement. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362810

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A closed, quantum, double barrier, GaAs/AlGaAs heterostructure is considered, and the dynamical behavior of an electron cloud moving in the heterostructure is examined. The motion of the electron cloud is represented by a mean field approximation, thus we have a representation of a nondissipative system which mixes in some region of its phase space, showing some chaotic characteristics. With the addition of the potential term &agr;⟨Q(t)⟩, the nonlinear, time‐dependent Schro¨dinger equation is solved for the amount of charge trapped in the heterostructure. As the nonlinear parameter &agr; increases, we find a tenfold increase in the Lyapunov exponent which provides a quantitative measure of the chaos inherent in the system. The phase space plots, autocorrelation function, and power spectrum are also discussed as a function of &agr;. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362811

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A method is presented to perform direct photoconductivity measurements of Sr0.61Ba0.39Nb2O6:Ce crystals at high intensities: A high voltage is applied to the sample and subsequent illumination yields a photocurrent through the crystal which charges a capacitor. Finally an electrometer measures the voltage of this capacitor. From voltage, capacity and exposure time the photoconductivity is calculated. Measurements with light pulses of a Q‐switched frequency‐doubled Nd:YAG laser (pulse duration 20 ns, light wavelength 532 nm) are performed. The photoconductivity &sgr;phincreases sublinearly with light intensityIaccording to &sgr;ph∝Ixwithx<1. The experimental results point to Ce3+/4+as the dominant photo‐ refractive center in Sr0.61Ba0.39Nb2O6:Ce at high intensities. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362812

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Arrays of tunnel junctions provide simple thermometric parameters in the limit where thermal excitations dominate over charging effects. We present numerical simulations for calculating the current versus voltage characteristics of an arbitrary one‐dimensional array at arbitrary temperatures on the premise of the ‘‘orthodox theory.’’ The purpose of the computer simulations is to investigate the suitability of tunnel junction arrays for thermometry at low temperatures when the analytical formulas do not hold and, specifically, to see the effect of background charges in this regime. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362813

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A systematic investigation of the transport properties of GdAs single crystals is presented. We report on measurements of the electric resistivity, magnetoresistance and Hall effect performed on a stoichiometric and a nonstoichiometric sample at temperatures between 1.6 and 300 K in fields up to 10 T. The stoichiometric sample behaved as a well compensated semimetal that orders antiferromagnetically, while the nonstoichiometric sample showed some anomalies that could be explained qualitatively by the model of trapped magnetic polarons. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362814

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have studied the defects created inp‐metal‐oxide‐semiconductor capacitors by Fowler– Nordheim injection. This injection has been performed either from the gate or from the substrate. We have shown that the oxide keeps no memory of the trapped holes created by an injection from the gate, once they have been neutralized. Nevertheless, we think that the corresponding traps are stress created by a mechanism similar to that which creates the slow states. The trapped hole annihilation has no influence on the number of interface states or slow states present after stress in the oxide. The increase of the interface state density with injected charge depends on whether the injection is from the gate or from the substrate. In both cases, the increase of the interface density differs from that of the trapped holes and slow states which suggests that the formation mechanisms of trapped holes and slow states are not the same as those of interface states. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362815

出版商:AIP    

年代:1996

数据来源: AIP