Volume 95, Issue 11, 01 June 2004
Index of content:
95(2004); http://dx.doi.org/10.1063/1.1715143View Description Hide Description
Measurements of the Hall-effect, photoluminescence (PL), and photocurrent(PC) have been made on Te-doped GaSe. The carrier transport for the Hall-effect measurement is dominated by the two acceptor levels at 0.08 and 0.02 eV above the valence band. The two acceptor levels have the same energy positions as the impurity levels in the PC spectra. By comparison with the results of GaSe grown with excess Se atoms, it was found that these acceptor levels are caused by the interstitial Te atoms. Moreover, the PC and PL spectra are dominated by the transition related to the indirect band and show the relaxation of the selection rule.
95(2004); http://dx.doi.org/10.1063/1.1728308View Description Hide Description
High-dielectric-constant (CCTO) thin films were prepared on substrates by pulsed-laser deposition (PLD). The 480 nm thick polycrystalline films have preferred orientation and show obvious crystallization on the surface. The temperature dependence of dielectric constant and loss of the Pt/CCTO/Pt capacitors is comparable with that obtained in the epitaxial CCTO filmsgrown on oxides substrates. We found that the dielectric properties are very sensitive to the postannealing atmosphere and temperature. Postannealing in nitrogen atmosphere produces larger low-frequency dielectric relaxation as the annealingtemperature increases, while annealing in oxygen atmosphere at high temperature suppresses the relaxation and decreases the dielectric constant of the thin films. Such results are attributed to the presence of insulating grain-boundary barrier layers.
95(2004); http://dx.doi.org/10.1063/1.1695604View Description Hide Description
The metal–insulator–silicon light-emitting diode (MIS LED) using a high-dielectric-constant material is studied. The external quantum efficiency for light emission at room temperature from the MIS LED was observed to be as compared to for the metal–oxide–silicon (MOS)LED. The large hole concentration at the interface created by the high dielectric constant of may be responsible for the enhancement. The emission line shape of the MIS LED can be fitted by the electron-hole plasma recombination model, similar to the MOSLED. The LED with a high interface trap density has a continuous spectrum below the Si gap beside the electron-hole plasma emission, probably due to the radiative recombination between the electrons and holes via the interface states.
95(2004); http://dx.doi.org/10.1063/1.1715131View Description Hide Description
We demonstrate a divergence-narrowed broad-area laser-diode array (LDA) with an external-cavity configuration that consists of a beam-transformation system and an off-axis reflecting mirror. Sixteen off-axis external-cavity laser diodes are formed for the high-power LDA. At a drive current of 21.2 A (four times the threshold current), the divergence angle full width at half maximum of the slow axis is reduced from without the external cavity to with the external cavity. The external-cavity LDA achieves a cw power output of 9.8 W, which is 60% of the free-running LDA.
95(2004); http://dx.doi.org/10.1063/1.1736319View Description Hide Description
A nanofluid is a fluid containing suspended solid particles, with sizes on the order of nanometers. Normally, nanofluids have higher thermal conductivities than their base fluids. Therefore, it is of interest to predict the effective thermal conductivity of such a nanofluid under different conditions, especially since only limited experimental data are available. We have developed a technique to compute the effective thermal conductivity of a nanofluid using Brownian dynamics simulation, which has the advantage of being computationally less expensive than molecular dynamics, and have coupled that with the equilibrium Green–Kubo method. By comparing the results of our calculation with the available experimental data, we show that our technique predicts the thermal conductivity of nanofluids to a good level of accuracy.