Magnetic frustration induced quantum phase transitions in the S=1/2 vertically asymmetric diamond chain

This work was supported by the National Basic Research Program of China (973 Program) grant No. G2009CB929300 and the National Natural Science Foundation of China under Grant Nos. 60521001 and 60776061.

ANTICROSSING DUE TO RESONANT COUPLING OF HOLE LEVELS IN ASYMMETRIC COUPLED-QUANTUM-WELLS

We present distinct evidence of anticrossing behavior for excitonic transitions due to resonant coupling of heavy-hole ground levels in a biased GaAs/Al0.35Ga0.65As/GaAs (50/40/100 angstrom) asymmetric coupled-double-quantum-wells p-i-n structure by using photoluminescence spectra. The minimum level splitting is about 2.5 meV.

LO-PHONON-ASSISTED TUNNELING IN ASYMMETRIC DOUBLE-WELL STRUCTURES WITH THICK BARRIERS

Nonresonant electron tunneling between asymmetric double quantum wells in AlxGa1-xAs/GaAs systems has been investigated by using steady-state and time-resolved photoluminescence spectra. Experimental evidence of LO-phonon-assisted tunneling through thick barriers has been obtained by enhancing excitation power densities or applying electric fields perpendicular to the well plane. LO-phonon-assisted tunneling times have also been estimated from the variation of the decay time of the narrow-well photoluminescence with applied electric fields. Our findings suggest that LO phonons in the barriers play an important role in the tunneling transfer.

INTERFACIAL REACTIONS IN THE CO/SI/GAAS AND SI/CO/GAAS SYSTEMS

The interfacial reactions between thin films of cobalt and silicon and (100)-oriented GaAs substrates in two configurations, Co/Si/GaAs and Si/Co/GaAs, were studied using a variety of techniques including Auger electron spectroscopy, x-ray diffraction, and transmission electron microscopy. The annealing conditions were 200, 300, 400, 600-degrees-C for 30 min, and rapid thermal annealing for 15 s. It was found that Si layer in the Co/Si/GaAs system acts as a barrier at the interface between Co and GaAs when annealed up to 600-degrees-C. The interfacial reaction between Co and Si is faster than that between Co and GaAs in the system of Si/Co/GaAs. The sequence of compound formation for the two metallizations studied (Co/Si/GaAs and Si/Co/GaAs) depends strongly on the sample configuration as well as the layer thickness of Si and Co (Co/Si atomic ratio). From our results, it is promising to utilize Co/Si/GaAs multilayer film structure to make a CoSi2/GaAs contact, and this CoSi2 may offer an alternative to the commonly used W silicides as improved gate metallurgies in self-aligned metal-semiconductor field effect transistor (MESFET) technologies.

MODELING OF ELECTRON-TUNNELING TIMES IN ASYMMETRIC DOUBLE QUANTUM-WELLS

A scattering process modeled by an imaginary potential V(I) in the wide well of an asymmetric double quantum well structure (DQWS) is used to model the electron tunneling from the narrow well. Taking V(I) approximately -5 meV, the ground resonant level lifetimes of the narrow well in the DQWS are in quantitative agreement with the experimental resonance and non-resonance tunneling times. The corresponding scattering time 66 fs is much faster than the intersubband scattering time of LO-photon emission.

INTERFACIAL FORMATION PROCESS AND REACTIONS BETWEEN AU AND HYDROGENATED AMORPHOUS SI STUDIED BY XPS AND AES

Interfacial formation processes and reactions between Au and hydrogenated amorphous Si have been studied by photoemission spectroscopy and Auger electron spectroscopy. A three-dimensional growth of Au metal cluster occurs at initial formation of the Au/a-Si:H interface. When Au deposition exceeds a critical time, Au and Si begin interdiffusing and react to create an Au-Si alloy region. Annealing enhances interdiffusion and a Si-rich region exists on the topmost surface of Au films on a-Si:H.

PHOTOEMISSION-STUDY OF THE INTERFACIAL FORMATION PROCESS AND REACTIONS BETWEEN AL AND HYDROGENATED AMORPHOUS SI

Using photoemission spectroscopy and Auger electron spectroscopy, the interfacial formation process and the reactions between Al and hydrogenated amorphous Si are probed, and annealing behaviors of the Al/a-Si:H system are investigated as well. It is found that a three-dimensional growth of Al metal clusters which includes reacted Al and non-reacted metal Al occurs at the initial Al deposition time, reacted Al and Si alloyed layers exist in the Al/a-Si:H interface, and non-reacted Al makes layer-by-layer growth forming a metal Al layer on the sample surface. The interfacial reactions and element interdiffusion of Al/a-Si:H are promoted under the vacuum annealing.