Experimental and theoretical studies are reviewed on the mechanism of instabilities of the coupled acoustic and optical modes in KDP type ferroelectrics. Light scattering spectra of the acoustic phonons depend upon temperature and the scattering wave vector: Emphasis is placed on the softening of the Brillouin shift and the appearance of a dynamical central component. These results are quantitatively explained as the spectra of the acoustic phonons coupled to a polarization relaxation mode which becomes unstable at a transition temperature. The x-dependence of the relaxation type spectra of mixed crystals KDP1-xDKDPx obtained in the 10cm-1 region can be well explained by taking account of the continuous x-dependence of the relaxation time of an independent dipole. Possible models of the phase transition in these ferroelectrics are discussed on the basis of these experimental results.
A review is given of magnetic resonance studies on defects in tetrahedrally bonded amorphous semiconductors, emphasizing the relation between defects and incorporated H and/or F. The results of ESR due to dangling bonds in a-Si: H, a-Si: F and a-Si: (F, H) are described including annealing effects. Then the origin of new ESR signals observed in P or B doped a-Si is described. The results of H and F NMR in a-Si: H, a-Si: F and a-Si: (F, H) are presented, and the promise of local H and F environments determination by NMR is discussed. Changes in the ESR signal with compositions of binary alloy systems, a-Si1-xCx, a-Si1-xGex and a-Ge1-xCx, are described. The relation between hydrogen attachment and dangling bond reduction among the component atoms is discussed from changes of the ESR and the infrared absorption with annealing. Finally, calculations of ESR g-values by a simple molecular orbital method are given and compared with the observed ones.
Present status of research on III-V compound semiconductor MIS interfaces is reviewed with particular emphasis on GaAs and InP. The following topics are discussed. (1) Summary and comparison of existing methods of oxidation and film deposition in terms of composition, structure of interface region and electrical properties. Interfacial chemical reactions of native oxides are briefly discussed. (2) Electrical characterization of MIS interfaces. MIS capacitance behavior, density-distribution and dynamic properties of interface-states are discussed, and various anomalies that are absent in Si MOS interface, are pointed out. As apossible explanation of these anomalies, authors' unified electrical modeling ofinterface is briefly described. (3) Origin of interface states. Existing models concerning the origin of compound semiconductor MIS interface states are roughly classified into three categories, and a brief comparative discussion is made. (4) Application of MIS interfaces to high-speed MISFET devices and ICs.Application to MIS solar cells is also briefly mentioned.
Plasma production by means of high-power pulsed-laser beam(s) from a solid target pellet has several unique features as compared with the other hot plasma production methods, particularly in connection with the problem of filling magnetic confinement devices with a clean hot plasma. This article reviews She principal results obtained from a series of systematic studies on this subject, performed mainly by the present authors' group, which include: (1) the fundamental properties of plasmas produced by Nd-glass- and/or CO2-laser beam(s), (2) thephysical processes involved in the strong interactions between rapidly expandinglaser-pro-duced plasma and surrounding external magnetic fields, (3) applications to specific type of magnetic bottles, and (4) the related theoretical problemsincluding computer simulations.
Quasi-two-dimensional electron gas accumulating at the heterojunction interface in selectively doped GaAs/N-AlxGal-xAs (x_??_O.3) grown byMBE showed extremely high mobility at low temperatures. The maximum mobilities attained at 77K and 4.2K were 117, 000cm2/Vs and 244, 000cm2/Vs, respectively, with sheet electron concentration of about 4.9x1011cm-2. Eventhe value at 77 K is almost 25 times as high as that of a conventional GaAs MESFET. High electron mobility transistors (HEMT's) were fabricated from the heterostructure material, which showed excellent high-speed performance at low temperatures. An enhancement-mode HEMT with a short gate (gate length LG=2μm, gate width WG=300μm) exhibited transconductance as high as 193ms/mm of the gate widthat 300 K and 409ms/mm at 77 K; the latter is the highest transconductance ever reported for field effect transistors. Consequently, this device has great potential for application as a post-silicon device in high-speed, low-power dissipation integrated circuits.