We have studied the origins of the leakage current in polycrystalline silicon (poly-Si) thin film transistors. Temperature dependent transfer characteristics were measured as a function of drain voltage. Three kinds of leakage current were introduced to explain the experimental results. The leakage current may arise from the generation current at very low drain voltage, and may result in the same activation energy between leakage current and conductivity of undoped poly-Si. The leakage current may be due to the thermionic field emission via grain boundary defects in the intermediate drain voltage region. At high drain voltage and high negative gate voltage, the leakage current may result from the field enhanced tunneling of electrons in the valence band to the conduction band via grain boundary traps.

We consider a finite type-II superlattice with different dielectric media on either side of the surfaces, which consist of unit cells with alternating electron and hole layers in the unit cell. Under some assumptions, we have studied the density-density correlation function including overlap effects between electron and hole wave functions of adjacent layers using the random-phase approximation. We have obtained the dispersion relation for surface and bulk plasmons in a few cases. Furthermore, we have calculated the Raman intensity in order to compare the result with those of others.

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A finite HgTe/CdTe superlattice with different dielectric media on either side of the surfaces is investigated by taking into account the wavefunction overlap between the interface states and plasmons. The unit cell of the finite HgTe/CdTe superlattice consists of two electronlike states and a heavy-hole-like state in HgTe and two light-hole-like states in CdTe. Using the random-phase approximation added with some assumptions, we have studied the densitydensity correlation function by considering the interface state with the wavefunctions overlapping with the electron-like states, the light-hole-like states and the heavy-hole-like states. We have calculated the collective excitation spectra of the intrasubband and the intersubband for both the bulk plasmons and the surface plasmons as a function of the number of unit cells. The Raman intensities due to bulk and surface plasmons are expressed by the relative value of the mode energy of the plasmons.

On the basis of the two-state model, the kinetics of hydrogen adsorption on a surface was studied as a function of temperature and time. Following this model, we formulated the hybridizing kinetics and obtained the sticking coefficient of the two-surface state in terms of the bulk fraction x by use of the method of Pick and Greene. We calculated the chemisorption energy and the activation energy for chemisorption by use of the theoretical calculation condition of Davenport, Pick and Greene, and Pick. The estimated chemisorption energy is 13.5-14.3 kcal/mol H and the activation energy for chemisorption is 0.8 -1.6 kcal/mol H. The relation between bulk fraction and heat rate was also obtained by application of the flash-desorption theory to this model.