Modelling of submarine landslides and generated water waves

The slide of unstable sedimentary bodies and their hydraulic effects are studied by numerical means. A two-dimensional fluid mechanics model based on Navier-Stokes equations has been developed considering the sediments and water as a mixture. Viscoplastic and diffusion laws for the sediments have been introduced into the model. The numerical model is validated with an analytical solution for a Bingham flow. Laboratory experiments consisting in the slide of gravel mass have been carried out. The results of these experiments have shown the importance of the sediment rheology and the diffusion. The model parameters are adjusted by trial and error to match the observed “sandflow”.

HYDROGEN DIFFUSION IN A-SI-H/A-SI STRUCTURE UNDER ELECTRICAL BIAS

By using the technique of elastic recoil detection (ERD), we have measured the hydrogen profiles in a-Si:H/a-Si structure samples annealed at various temperatures with and without electrical bias, and investigated the influence of electrical bias on hydrogen diffusion. The results show that hydrogen diffusion in a-Si is significantly enhanced by the action of electrical bias. The existence of the excess carriers, which are introduced by electrical injection, is considered to be responsible for the enhancement of hydrogen diffusion, and the microprocess of hydrogen transport has been exploited.

THE MODULATION PRINCIPLE OF VACUUM ON THE SUPERCONDUCTIVITY OF YBCO

By neutron diffraction and other experiments, we have found that oxygen ions in YBCO can diffuse out of the sample in vacuo at room and low temperature, while the T(c) decreases greatly. We have also found that if the vacuum-deoxidation process lasts for several days there will be a damping oscillation of T(c) with time (t), and higher vacuum corresponds to a greater amplitude and a shorter period. We tentatively think that T(c) should satisfy the following function: T(c0) is-proportional-to T(c)e(-betat)cos (omegat + phi); it may be due to the diffusion of oxygen and the saturation of the valence state.

A NEW METHOD FOR MEASURING THE EFFECTIVE DIFFUSION CONSTANT OF 2-DIMENSIONAL ELECTRONS IN THE PRESENCE OF MAGNETIC-FIELDS

The transient charge response Q(t) of a two-dimensional electron gas (2DEG) in GaAs/AlxGa1-xAs heterostructures to a small pulse of the gate voltage, applied between the top gate and source electrodes in a Corbino structure, was employed to directly measure the effective diffusion constant of a 2DEG in the quantum Hall regime. The measured diffusion constant D showed a drastic change as the magnetic field was swept through the integer fillings of the Landau levels.

808 nm high-power laser grown by MBE through the control of Be diffusion and use of superlattice

808 nm high-power laser diodes are gown by MBE. In the laser structure, the combination of Si-doped GRIN (graded-index) region adjacent to n-AlGaAs cladding layer with reduced Be doping concentration near the active region has been used to diminish Be diffusion and oxygen incorporation. As compared with the laser structure which has undoped GRIN region and uniform doping concentration for Si and Be, respectively, in the cladding layers, the slope efficiency has increased by about 8%. Typical threshold current density of 300 A/cm(2) and the minimum threshold current density of 220 A/cm(2) for lasers with 500 mu m cavity length are obtained. A high slope efficiency of 1.3 W/A for coated lasers with 1000 mu m cavity length is also demonstrated, Recorded CW output power at room temperature has reached 2.3 W.

Diffusion of ion implanted as in Si1-xGex epilayers

Diffusion of implanted As ion in relaxed Si1-xGex was studied as a function of Ge content over a wide range of Ge fractions (0-43%) and annealing temperature, and was compared to diffusion in Si. Experimental results showed that the As diffusion is enhanced with increasing annealing temperature for certain Ge content and strongly dependent on the higher Ge content and the faster As diffusion.

Quantum Well Intermixing of InGaAsP QWs by Impurity Free Vacancy Diffusion Using SiO_2 Encapsulation

Experiment on quantum well intermixing (QWI) of InGaAsP QWs by impurity free vacancy diffusion (IFVD) using SiO_2 encapsulation is reported. A maximum band gap wavelength blue-shift as large as 200nm is realized. Furthermore, an FP laser blue-shifted 21nm by QWI is fabricated with characteristics comparable with the asgrown one.

Light induced rapid thermal diffusion of boron atom in silicon

国家自然科学基金

Influence of open-tube Ga diffusion on the characteristics for thyristor

Open-tube Ga diffusion into a SiO2/Si structure was used for fabrication of the high speed thyristor. The advantages of open-tube Ga diffusion are as follows; it is easier to operate and easier to control the profile of the Ga concentration during processing, a clean surface, which is free from alloy spots can be obtained, this technique ensures to improve the on-state characteristics and dynamic characteristics.

Boron diffusion in Ge+ premorphized and BF2+ implanted Si(001)

The annealing behavior of Si implanted with Ge and then BF2 has been characterized by double crystal X-ray diffraction (DCXRD) and secondary ion mass spectroscopy (SIMS). The results show that annealing at 600 degrees C for 60 minutes can only remove a little damage induced by implantation and nearly no redistribution of Ge and B atoms has occurred during the annealing. The initial crystallinity of Si is fully recovered after annealing at 950 degrees C for 60 minutes and accompanied by Ge diffusion. Very shallow boron junction depth has been formed. When annealing temperature rises to 1050 degrees C, B diffusion enhances, which leads to a deep diffusion and good distribution of B atoms into the Si substrate. The X-ray diffraction (004) rocking curves from the samples annealed at 1050 degrees C for 60 minutes display two SiGe peaks, which may be related to the B concentration profiles.

The enhancement of diffusion by strain of InAs quantum dots in a GaAs matrix

We investigate the annealing behavior of Photoluminescence (PL) from self-assembled InAs quantum dots (QDs) with different thicknesses GaAs cap layers. The diffusion introduced by annealing treatment results in a blue-shift of the QD PL peak, and a decrease in the integrated intensity. The strain present in QDs enhances the diffusion, and the QDs with the cap layers of different thicknesses will experience a strain of different strength. This can lend to a, better understanding of the larger blue-shift of the PL peak of the deeper buried QDs, and the different variance of the full width at half maximum of the luminescence from QDs with the cap layers of different thicknesses.