1.5 mu m luminescence characteristic of erbium in B, P doped a-SiO : H films

Hydrogenated amorphous silicon films co-doped with oxygen (O), boron (B) and phosphorus (P) were fabricated using PECVD technique. The erbium (Er) implanted samples were annealed in a N-2 ambient by rapid thermal annealing. Strong photoluminescence (PL) spectra of these samples were observed at room temperature. The incorporation of O, B and P could not only enhance the PL intensity but also the thermal annealing temperature of the strongest PL intensity. It seems that the incorporation of B or P can decrease the grain boundary potential barriers thus leading to an easier movement of carriers and a stronger PL intensity. Temperature dependence of PL indicated the thermal quenching of Er-doped hydrogenated amorphous silicon is very weak.

Degenerate four-wave-mixing signals from dc- and ac-driven semiconductor superlattice

Within the one-dimensional tight-binding model;rnd chi-3 approximation, we have calculated four-wave-mixing (FWM) signals for a semiconductor superlattice in the presence of both static and high-frequency electric fields. When the exciton effect is negligible, the time-periodic field dynamically delocalizes the otherwise localized Wannier-Stark states, and accordingly quasienergy band structures are formed, and manifest in the FWM spectra as a series of equally separated continua. The width of each continuum is proportional to the joint width of the valence and conduction minibands and is independent of the Wannier-Stark index. The realistic homogeneous broadening blurs the continua into broad peaks, whose line shapes, far from the Lorentzian, vary with the delay time in the FWM spectra. The swinging range of the peaks is just the quasienergy bandwidth. The dynamical delocalization (DDL) also induces significant FWM signals well beyond the excitation energy window. When the Coulomb interaction is taken into account, the unequal spacing between the excitonic Wannier-Stark levels weakens the DDL effect, and the FWM spectrum is transformed into groups of discrete lines. Strikingly, the groups are evenly spaced by the ac field frequency, reflecting the characteristic of the quasienergy states. The homogeneous broadening again smears out the line structures, leading to the excitonic FWM spectra quite similar to those without the exciton effect. However, all these features predicted by the dynamical theory do not appear in a recent experiment [Phys. Rev. Lett. 79, 301 (1997)], in which, by using the static approximation the observed Wannier-Stark ladder with delay-time-dependent spacing in the FWM spectra is attributed to a temporally periodic dipole field, produced by the Bloch oscillation of electrons in real space. The contradiction between the dynamical theory and the experiments is discussed. In addition, our calculation indicates that the dynamical localization coherently enhances the time-integrated FWM signals. The feasibility of using such a technique to study the dynamical localization phenomena is shown. [S0163-1829(99)10607-6].

High Characteristic Temperature 1.3 mu m InAs/GaAs Quantum-Dot Lasers Grown by Molecular Beam Epitaxy

We report the molecular beam epitaxy growth of 1.3 mu m InAs/GaAs quantum-dot (QD) lasers with high characteristic temperature T-0. The active region of the lasers consists of five-layer InAs QDs with p-type modulation doping. Devices with a stripe width of 4 mu m and a cavity length of 1200 mu m are fabricated and tested in the pulsed regime under different temperatures. It is found that T-0 of the QD lasers is as high as 532K in the temperature range from 10 degrees C to 60 degrees C. In addition, the aging test for the lasers under continuous wave operation at 100 degrees C for 72 h shows almost no degradation, indicating the high crystal quality of the devices.

Characteristic of the ultrawideband electromagnetic radiation generated by PCSS

A novel ultra-wideband electromagnetic pulse generating method based on the photoconductive semiconductor switches (PCSS) is presented. Gallium arsenide is used to develop the PCSS for an ultrashort electromagnetic pulse source. The pulse generated by such PCSS is within picosecond (ps) time scale, and can yield power pulse with an voltage over 10 kV. The experimental results show that the pulses are stable, with the peak-peak amplitude change of 6% and the time jitter within several picoseconds. The radiations of the PCSS triggered by the picosecond laser and fenitosecond laser pulse series illustrate that the electromagnetic pulses would have high repetition of more than 80 MHz and frequency bandwidth of DC-6 GHz. The radiations of "lock-on " mode of the PCSS are also analyzed here. (c) 2007 Wiley Periodicals, Inc.

Radiation hardness characteristic of N-implanted and F-implanted SIMOX/NMOSFET

Radiation hardness of SIMOX(separation by implanted oxygen)/NMOSFET by implanting N and F ion has been carefully studied in this paper.Both N and F ion implantation can reduce hole traps in the buried oxide and the interfacial regions,which consequently improves the radiation hardness,especially under high dose radiation conditions.Moreover,experimental data show that the higher dose of the N and F ion implantation is,the better radiation hardness is achieved.In order to minimize the influence on the threshold voltage of devices,it is important to choose suitable implantation dose and energy of N or F implantation that have smaller impact on the preradiation device performance.

High Characteristic Temperature InGaAsP/InP Tunnel Injection Multiple-Quantum-Well Lasers

We fabricate 1.5 mu m InGaAsP/InP tunnel injection multiple-quantum-well (TI-MQW) Fabry-Perot (F-P) ridge lasers. The laser heterostructures, including an inner cladding layer and an InP tunnel barrier layer, are grown by metal-organic chemical-vapor deposition (MOCVD). Characteristic temperature.. 0 of 160K at 20 degrees C is obtained for 500-mu m-long lasers. T-0 is measured as high as 88K in the temperature range of 15-75 degrees C. Cavity length dependence of T-0 is investigated.

Application of the characteristic CIP method to a shallow water model on the sphere

Semi-implicit algorithms are popularly used to deal with the gravitational term in numerical models. In this paper, we adopt the method of characteristics to compute the solutions for gravity waves on a sphere directly using a semi-Lagrangian advection scheme instead of the semi-implicit method in a shallow water model, to avoid expensive matrix inversions. Adoption of the semi-Lagrangian scheme renders the numerical model always stable for any Courant number, and which saves CPU time. To illustrate the efficiency of the characteristic constrained interpolation profile (CIP) method, some numerical results are shown for idealized test cases on a sphere in the Yin-Yang grid system.

Characteristic rainfall for warning of debris flows

A characteristic rainfall is introduced to overcome the difficulties encountered in determining a critical rainfall value for triggering debris flow. The characteristic value is defined as the rainfall at which debris-flow occurrence probability shows a rapid increase, and can be used as a warning rainfall threshold for debris flows. Investigation of recorded debris flows and 24-hour rainfall data at Jiangjia basin, Yunnan Province, in southwestern China, demonstrates the existence of such a characteristic rainfall. It was found that the characteristic rainfall corresponds to the daily rainfall of 90% cumulative probability by analyzing the basin's daily rainfall histogram. The result provides a simple and useful method for estimating a debris-flow warning rainfall threshold from the daily rainfall distribution. It was applied to estimate the debris-flow warning rainfall threshold for the Subaohe basin, a watershed in the 2008 Wenchuan earthquake zone with many physical characteristics similar to those of the Jiangjia basin.