Koziro Narita

Nuclear Magnetic Resonance Powder Patterns of the Second‐Order Nuclear Quadrupole Interaction in Solids with Asymmetric Field Gradient

Numerical calculations of the powder pattern of the central component shifted by the second‐order nuclear quadrupole interaction in solids have been performed for various values of the asymmetry parameter, η. Shape functions have been obtained in units of (νQ2/6νL) (a—¾) for η=0.1, 0.2, ···, 1.0, at 0.1 intervals. Also, positions of special points such as infinities and steps of the shape function have been determined as functions of η. Effects of the dipolar broadening of the single‐crystal resonance upon powder patterns have been estimated for the case of η=0.5. Influences of anisotropic magnetic shift were also discussed on powder patterns obtained experimentally. These relations are useful for simple and rapid determinations of η and νQ from the second‐order powder pattern.

Transport properties of conduction electrons in n-type inversion layers in (100) surfaces of silicon

Abstract The conductivities of n -type inversion layers in (100) surfaces of p -type silicon were measured extensively as functions of electron density in the inversion layer, the ambient temperature and the applied magnetic field. Measurements were made on the carefully fabricated four “classes” of MOS field-effect transistors whose maximum mobilities at 4·2K were 14,000, 8000, 6800 and 1500 cm 2 /V·sec, respectively. From the temperature dependence of the mobility, dominant momentum scattering was reasonably ascribed to surfon at 100 ∼ 300 K. and degenerate or non-degenerate coulomb scattering at lower temperatures as treated by Stern and Howard. From the curves of conductivity vs temperature at low temperatures and low electron concentration for specimens with high mobilities, an activation energy of 1·2 meV, relating to the shallow bound states associated with the lowest electrin sub-band, was observed. The conductivity σ xx of the inversion layer in a strong transverse magnetic field showed behaviors like those of completely free electrons without effects belonging to its material in its oscillation pattern. That is, the peak value of σ xx as a function of the gate voltage V R dependend only on the Landau index. The σ xx as a function of the magnetic field H at a constant V R showed a similar Shubnikov-de Haas (SdH) type oscillation to that of three dimensional one. The SdH oscillation gave an “apparent” g -value g * which ranges from 2 to 5 depending on the surface carrier density n s , due to the change in the ratios of the widths of the Landau levels to the level separation. The “reasonable” g -value of the conduction electrons in the inversion layer has been determined using a modified tilted magnetic field method. The g -value at the fixed magnetic field was independent of surface carrier density n s and tended to 2 in the extreme strong magnetic field. Discussion is made of the g -value relating to the Landau level width and the energy gaps in the density of states under strong magnetic field.

A model for exciton bound to a donor pair in silicon

Abstract A model that an exciton is bound to a pair of donors is proposed to explain the characteristic features of photoluminescence in phosphorus doped silicon, recently observed by Shiraki and Nakashima. In order to substantiate the model, the energy of the exciton bound to a pair of donors is estimated. It is found that calculated line shape for photoluminescence is quite satisfactory both in magnitude of its line width and dependence of its symmetry on the donor concentration.

On the g factor for electrons in n-type silicon surface inversion layers

Abstract Self-consistent calculations for energy levels are performed for n-type inversion layers of silicon with magnetic field perpendicular to the (100) surface. ‘Apparent’ g factor g∗, obtained from the period of oscillation of states density at Fermi level for varying magnetic field, is plotted as a function of the Γ 2βH , where Γ is the width of Landau levels. The results show that g ∗ ∼ g for Γ ⪢ 2β H, and g ∗ ∼ 5 for Γ H . This means that we should be very careful when interpret the g shift of electrons in inversion layers for small surface electron density.

Conductance Anomalies and Electronic States in Silicon Inversion Layers near Threshold at Low Temperatures

The conductivity of n -type inversion layers in silicon MOS field-effect transistors near threshold is studied as a function of electron concentration n s , temperature and magnetic field. In the specimens with a small amount of disorder at the interfaces, the inversion layer conductivity at low concentrations n s <10 11 cm -2 shows a sharp maximum at around 13 K. This anomalous enhancement of inversion layer conductivity is discussed relating to the Wigner crystallization.

ESR Study of Tb3+ and Pr3+ in La2O2S Single Crystals

The electron spin resonance of Tb 3+ and Pr 3+ ions in La 2 O 2 S single crystals in investigated. The symmetry of the centers were determined with the help of crystal structure considerations. Models for these centers are proposed and the electronic structures of the ground state are discussed. For the Tb 3+ ion, there are two types of centers, the symmetry of which are characterized by C 3υ and C 1 h , whereas only one type of center with C 3υ symmetry was observed for Pr 3+ ion. The centers having C 3υ symmetry are considered to be Tb 3+ and Pr 3+ ions which are substituted for La 3+ ion in the host crystal. The line shape is asymmetric, probably due to the dynamical Jahn-Teller effect of non-Kramers doublet. The center with C 1 h symmetry is supposed to be the Tb 3+ ion which is substituted for the La 3+ ion with some defect at the nearest sulphur site.

Effects of Impurity Compensation on Electrical Properties of p‐Type Germanium under Hydrostatic Pressure

The fractional change of resistivity Δρ/ρ0 under hydrostatic pressure up to 30 kbar and Hall effect up to 10 kbar have been measured in Cu‐doped germanium samples with acceptor concentration Na ranging from 1013 to 3.96 × 1016 cm−3, and with compensation ratios K from 0.38 to 0.968. Δρ/ρ0 increases from negative to positive values with increasing K. The experimental behavior of Δρ/ρ0 with hydrostatic pressure P is divided into four categories: (i) negative and linear for Na ∼ 1015 cm−3 and small K; (ii) positive and linear for Na ≥ 3.4 × 1015 cm−3 and 0.7 ≤ K ≤ 0.968; (iii) sublinear for Na < 3 × 1014 cm−3 and any K; and (iv) superlinear (or exponential) and positive for Na ∼ ni, where ni is the intrinsic carrier concentration. These features were analyzed theoretically. A good agreement between analytical calculations and the data is obtained if the values d(lnμhL)/dP = 6.2 × 10−3 kbar−1 and d(lnμhI)/dP = −14.4 × 10−3 kbar−1 are used, where μhL and μhI are the lattice and ionized impurity scattering mobi...