Collective excitations in the coupled quantum wires

The dielectric response of an electron system composed of an array of parallel quantum wires with weak coupling and strong coupling are studied, and the dispersions of the collective excitations and the single particle excitations (SPE) as functions of wave-vectors are given. It is found that for the nearly isolated quantum wires with several subbands occupation, there are a series of intra-subband collective excitations between corresponding intra-subband SPE spectra. There also exist inter-subband collective excitations when q(x) not equal 0 (q(x) is the wave-vector component in the modulation direction), whose energies are close by the corresponding inter-subband SPE spectra. The energy of the intra-subband mode decreases and that of inter-subband mode increases with q(x) increasing. The collective excitation dispersions show obvious anisotropy in the 1D quantum limit. The calculated results agree with the experiment well. The coupling between quantum wires affects markedly both the collective and single-particle excitations spectra. The system changes to a near-two-dimensional electron system gradually with increasing coupling.

Collective excitations in coupled quantum wells

The dielectric response of a modulated three-dimensional electron system composed of a periodic array of quantum wells with weak coupling and strong coupling are studied, and the dispersions of the collective excitations and the single particle excitations as functions of wave vectors are given. It is found that for the nearly isolated multiple-quantum-well case with several subbands occupation, there is a three-dimensional-like plasmon when q(z)=0 (q(z) is the wave-vector component in the superlattice axis). There also exist intersubband collective excitations in addition to one intra-subband mode when q(z) not equal 0. The intra-subband mode has a linear dispersion relation with q(//) (the wave-vector component perpendicular to the superlattice axis) when q(//) is small. The inter-subband modes cover wider ranges in q(//) with increasing values of q(z). The energies of inter-subband collective excitations are close by the corresponding inter-subband single-particle excitation spectra. The collective excitation dispersions show obvious anisotropy in the 2D quantum limit. The calculated results agree with the experiment. The coupling between quantum wells affects markedly both the collective excitations and the single particle excitations spectra. The system shows gradually a near-three-dimensional electron gas character with increasing coupling. Copyright (C) 1996 Published by Elsevier Science Ltd

Ge composition saturation behavior during low-temperature Si1-xGex growth by disilane and solid Ge molecular beam epitaxy

Ge composition dependence on the Ge cell temperature has been studied during the growth of Si1-xGex by disilane and solid Ge molecular beam epitaxy at a substrate temperature of 500 degrees C. It is found that the composition x increases and then saturates when the Ge cell temperature increases, which is different from the composition-dependent behavior in growth at high temperature as well as in growth by molecular beam epitaxy using disilane and germane. The enhanced hydrogen desorption from a Ge site alone cannot account for this abnormal composition-variation behavior. We attribute this behavior to the increase of rate constant of H desorption on a Si site when the Ge cell temperature increases.

COMPARISON OF PROPERTIES OF SOLID-PHASE EPITAXIAL SILICON-ON-SAPPHIRE FILMS RECRYSTALLIZED BY RAPID THERMAL ANNEALING AND FURNACE ANNEALING

Chemically vapour deposited silicon on sapphire (SOS) films 0.25 mu m thick were implanted with Si-28(+) and recrystallized in solid phase by furnace annealing (FA) and IR rapid thermal annealing (RTA) in our laboratory. An improvement in crystalline quality can be obtained using both annealing procedures. After FA, it is hard to retain the intrinsic high resistivity value(10(4)-10(5) Ohm cm) observed in as-grown SOS films, so the improvement process cannot be put to practical use effectively. However, it is demonstrated that by properly adjusting the implantation and RTA conditions, significant improvements in both film quality and film autodoping can be accomplished. This work describes a modified double solid phase epitaxy process in which the intrinsic high resistivities of the as grown SOS films are retained. The mechanism of suppression of Al autodoping is discussed.

GaInNAs/GaAs quantum well lasers grown by solid-source molecular beam epitaxy

The growth of GaInNAs/GaAs quantum wells (QW) was investigated by solid-source molecular beam epitaxy. N was introduced by a dc-active plasma source. The effect of growth conditions such as on the N incorporation and photoluminescence (PL) intensity of the QWs has been studied. The PL peak intensity decreased and the PL fun width at half maximum increased with increasing N concentrations. The highest N concentration of 2.6% in a GaInNAs/GaAs QW was obtained, and corresponding to a PL peak wavelength of 1.57 mum at 10K. Rapid thermal annealing at 850degreesC significantly improved the crystal quality of the QWs. An optimum annealing time of 5s at 850degreesC was obtained. A GaInNAs/GaAs SQW laser with the emitting wavelength of 1.2 mum and a high characteristic temperature of 115 K was achieved at room temperature.

Improvement of CMOS SOS devices characteristics by a modified solid phase epitaxy

CMOS/SOS devices have lower carriers mobility and higher channel leakage current than bulk silicon CMOS devices. These mainly results from the defects of heteroepitaxial silicon film, especially from the defects near Si-Sapphire interface. This paper describes the experiment results of CMOS/SOS devices characteristics improved by a better epitaxial silicon quality which is obtained by a modified solid phase epitaxy.

Improvement of thin silicon on sapphire (SOS) film materials and device performances by solid phase epitaxy

The increased emphasis on sub-micron CMOS/SOS devices has placed a demand for high quality thin silicon on sapphire (SOS) films with thickness of the order 100-200 nm. It is demonstrated that the crystalline quality of as-grown thin SOS films by the CVD method can be greatly improved by solid phase epitaxy (SPE) process: implantation of self-silicon ions and subsequent thermal annealing. Subsequent regrowth of this amorphous layer leads to a greater improvement in silicon layer crystallinity and channel carrier mobility, evidenced, respectively, by double crystal X-ray diffraction and electrical measurements. We concluded that the thin SPE SOS films are suitable for application to high-performance CMOS circuitry. (C) 2000 Elsevier Science S.A. All rights reserved.