| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1999: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1998: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1997: ¥700,000 (Direct Cost: ¥700,000)
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| Research Abstract |
With increase in adsorption coverage, a carrier-depletion or carrier-accmulation layer is often formed at a doped semiconductor surface. At the first stage of the present work, using the local-density approximation (LDA), we have analyzed the variation in ground and thermal-equilibrium states in the depletion-layer (D-L) formation process. We have found the variation and the temperature effect in the carrier-density profile. Next, on the basis of the calculated result of thermal-equilibrium states and by means of the time-dependent LDA, we have made a systematic analysis of evolution of surface elementary excitations in the D-L formation process. The elementary excitations studied here are two coupled carrier plasmon (PL)-polar phonon (PH) modes A and B and the surface polar-PH mode C involving screening charges due to presence of carriers. The major results are summarized as follows :
(1) We have examined the evolution of the energy dispersion and the energy-loss intensity of each mode
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in the D-L formation process. In the mode A or B, an initial upward dispersion branch shifts downward, and evolves into a warped one.
(2) The variation in coupling character of PL and PH in the D-L formation process has been clarified by investigating the phase relation and the amplitude ratio of the carrier and the PH components in the induced charge-density distribution.
(3) The contour-map analysis of the induced charge-density distribution has exhibited a significant variation in spatial structure of the mode A or B in the D-L formation process. In the mode C, it has shown how the surface polar phonon propagates along the surface dragging screening charges and how the screening-charge distribution varies in the process.
(4) Our analysis has given a clear explanation of the experimental result of high-resolution electron energy-loss spectroscopy (HREELS).
In addition, our kinematic analysis of HREELS with the specular-reflection geometry has indicated that, with a grazing incident angle fixed and with the incident energy varied in a broad range, we can scan a narrowed probing dispersion region to make a close observation of the dispersion relation of such surface-excitation modes as studied here.
It has become a future problem to analyze the evolution of surface elementary excitations in an accumulation-layer formation process. Less
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