Hatsuo Kimura

Free-Carrier Infrared Absorption and Determination of Deformation-Potential Constant in n-type InSb

A quantum mechanical theory of the infrared absorption by conduction electrons in InSb is developed according to the second-order perturbation formula in degenerate cases. The absorption coefficient due to acoustical phonons is calculated by means of the deformation-potential method. The deformation-potential constant E 1 is only contained as an unknown parameter and the values of the other quantities are obtainable from measurements. The magnitude of E 1 can be easily determined from the comparison between the theory and experiments, and thus an information about the scattering mechanism is obtainable. When | E 1 | is taken as 30 eV, the present theory is in excellent agreement with the experiment of Kessler and Sutter for various carrier concentrations and wave lengths and also with that of Spitzer and Fan for a more wide range of wavelength. It is also shown that the theoretical value of the optical cross section for free electrons in pure materials is quite consistent with the value found by Kurnick a...

Free-Carrier Infrared Absorption in III-V Semiconductors III. GaAs, InP, GaP and GaSb

The free carrier absorption data for n -GaAs, -InP, -GaP and -GaSb are analysed in order to investigate the scattering mechanism of electrons. The magnitudes of the deformation potential constant E 1 are found to be ∼6 eV for GaAs, ∼0 eV for InP, ∼55 eV for GaP and ∼60 eV for GaSb. It is found from this that, among acoustic and optical phonon scatterings, the former is predominant in GaP and GaSb, and the latter predominant in GaAs and InP. The impurity concentration is found to be very large compared with the electron concentration, for the samples of GaAs and InP with low carrier concentrations. This suggests the presence of some additional scatterers different from the ordinary ones, that is, lattice vibrations and ionized impurities. From the present analysis, it is inferred that the absorption coefficient due to additional scatterers have a wavelength dependence very similar to the one due to ionized impurities.

Nematic Ordering of Rod-Like Molecules Interacting via Anisotropic Dispersion Forces as well as Rigid-Body Repulsions

A theory of nematic ordering in liquid crystals has been developed. The method of symmetry-breaking potential and a first-order cluster expansion technique for the partition function are employed. The obtained results agree with those of the Onsager-Isihara (for hard rods) and of the Meiar-Saupe (for dispersion forces) theories in respective limiting cases. The nematic order parameter is calculated as a function of temperature and density of liquids; the calculated values agree very well with the experimental ones on nematic para-azoxyanisole for the pressure range from 1 to 640 ber. The nematic-isotropic transition temperature T c is calculated as a function of the density and shape of molecules (length, breadth and their ratio). The theory provides good explanations, at least qualitatively, of behavior of T c for various homologous series of nematic liquid crystals.

Nematic-Smectic Transition in an Aligned Rod System

The nematic-smectic transition in the system of completely aligned hard cylindrical rods is investigated, by making use of the method of symmetry breaking potential. In the second virial approximation the transition is found to occur in the 3-dimensional system but not in the 1- and 2-dimensional systems, in contrast with the result obtained by Wadati and Isihara that the 2-dimensional system also exhibits such a transition. It is shown that the transition is very like the second order one. A shape effect is also studied. Furthermore, by introducing an isotropic attractive intermolecular force, the dependence of the transition on the strength of that force as well as the length and diameter of the rod molecule is investigated.

Quantum Statistical-Mechanical Theory of Optical Activity

The expression for the electric current density induced in a system by an incident polarized beam is obtained on the basis of quantum statistical mechanical theory of linear response. It is expressed as a sum of time and space derivatives of the electric polarization and quadripole moment density and of the magnetization. In the case of the solution averaging over whole molecular orientations are applied. By solving the Maxwell equations with substitution of the averaged current density, what sort of polarized beam can travel through the solution is investigated. In the solution of randomly-oriented molecules the contribution from the quadripole moment density vanishes and the usual theory for the solution is attained. In the uniaxially symmetric case of molecular-orientation probability a linearly polarized beam travelling in the direction of the symmetry axis exhibits the optical rotation and circular dichroism, where the quadripole moment density contributes to the phenomena.

Free-Carrier Infrared Absorption in III-V Semiconductors IV. Inter-Conduction Band Transitions

The infrared absorption bands observed in 1∼5 µ are theoretically investigated under the assumption that the absorption is due to the transition of electrons between two conduction bands which have the minima being located at different points in the zone. With use of the second order perturbation in the presence of photons and crystal imperfections, the theoretical curves give different shapes according as the possible intermediate states are the D - or I -type. The first has a sharp peak in the absorption band, while the latter forms a broad band. For AlSb and GaSb, the observed shapes of the absorption bands agree reasonably with the calculated ones for the D - type . The carrier concentration dependence of the absorption coefficient in AlSb can also be explained fairly well. For GaAs, the absorption band calculated for the I - type agrees well with the experimental one at the points of the shape, the carrier concentration dependence and the temperature dependence. Also, the gap energy between two minim...

Statistical Theory of Cholesteric Ordering in Hard-Rod Fluids and Liquid Crystalline Properties of Polypeptide Solutions

A statistical theory of lyotropic cholesteric phase in the system of long coiled rod molecules is presented. Effects of molecular exclusion and of attractive intermolecular force are both taken into consideration. On the basis of the theoretical results, experiments on the cholesteric solutions of polypeptide are investigated, where use is made of the scaled particle theory on the fluid of hard rod molecules. It is thus found that the experimental dependences of cholesteric twisting power on temperature, concentration and molecular weight of the polymer and also the experimental curvature elasticity are explained satisfactorily.

Electronic Properties for Pd Metal and Its Ferromagnetic Alloys –On the Number of Holes in the 4d-Band of Pd Metal–

By making use of a new experimental fact that the number of electrons in the 5 s -band or the number of holes in the 4 d -band is 0.36 per atom for Pd metal, the composition dependence of the magnetization of Pd-Fe and Pd-Co alloys is discussed, and residual electric resistivities for Ni-Pd alloys are calculated. Using the density of states curve which has been determined. from the low temperature specific heat data and modified by taking account of this new fact, the temperature dependence of the electronic specific heat and the paramagnetic susceptibility of Pd metal is calculated. The new value of the number of holes or electrons can give better interpretation of the experimental results than the value 0.6 per atom, which has so far been believed to be most probable.

Effect of Orientational Fluctuation on Nematic-Smectic A Transition in the System of Hard Rod Molecules

By applying the method of symmetry breaking potential to Zwanzigs three direction model for liquid crystal, the nematic-smectic as well as isotropic-nematic transitions are investigated. Particular attention is paid to the effect of orientational fluctuation on the nematic-smectic A transition. It is shown that the nematic-smectic A transition is reduced to the one of first order owing to that kind of fluctuation for the case of short molecule.

Free-Carrier Infrared Absorption in III-V Semiconductors II. InAs

An analysis for the infrared absorption by free carriers in n -type InAs is carried out on the basis of the previous theory developed for n -type InSb, in order to investigate the scattering mechanism. The magnitude of the deformation potential constant E 1 is found to be 10 eV , and it is found that the contribution from acoustical phonons is not important for all samples of Dixon. The impurity concentration is found to be N imp =11 N e for the sample A of the smallest carrier concentration: N e =2.8×10 16 cm -3 , and to be N imp = N e for the other samples. Optical phonons make the most important contribution for samples of relatively low carrier concentrations except the sample A , in which the contribution from impurities is comparable to the one from optical phonons. The presence of an unknown scatterer in the sample A is suggested and a discussion for this is given. A discussion on the screened Coulomb potential used in the calculation of the impurity scattering also is given.