J. Wakabayashi

Quantum galvanomagnetic properties of n-type inversion layers on Si(100) MOSFET

Abstract Transverse magnetoconductivity σxx and Hall effect in n-type inversion layers of Si(100) MOSFET are measured for various source-drain fields between 0.08 and 40 V/cm under magnetic fields up to 150 kOe at 1.4 K. Conductivity peaks in low Landau levels are in good agreement with theory. Effect of the source-drain field in the magnetoconductivity is found to be very important in higher Landau levels as well as in the appearance of the lowest Landau level peak. Immobile electrons are clearly observed in conductivity bottoms. Electrode geometry effect for Hall effect measurement under strong magnetic fields is discussed.

Temperature dependence of the magnetoconductivity in the ground Landau level in silicon inversion layers

Abstract The magnetoconductivity σ xx in the lower edge of the lowest Landau level in silicon inversion layers shows an activation type temperature dependence in H = 97.5 kOe and T = 4.2−1.5 K. An attempt is made to describe the experimental results by a simple model based on the quantum diffusion of Schottky defects in the two-dimensional Wigner crystal.

Experiments on the Critical Exponent of Localization in Landau Subbands with the Landau Quantum Numbers 0 and 1 in Si-MOS Inversion Layers

Temperature ( T ) dependence of the mobility edge is examined by a model calculation which reproduces the experimental line shape of dσ x y /d N s (σ x y : Hall conductivity, N s : electron concentration) for (0↓-) and (1↑-) Landau subbands in Si-MOS inversion layers in the range of 0.35 K≦ T ≦1.5 K and in a magnetic field of 15 T. The result show that the critical behaviour of localization depends on the Landau quantum number.

Temperature Dependence of Transverse and Hall Conductivities of Silicon MOS Inversion Layers under Strong Magnetic Fields

An n-channel MOS inversiln layer on Si (100) surface is a typical two-dimensilnal electrln system. When a strlng magnetic field is applied along a directiln nlrmal tl the Si-SiO2 interface, the continuum of electron energy levels in two-dimensilnal mltiln clalesces intl a series lf perfectly quantized Landau levels [1], In such a system in an extreme-quantum-limit clnditiln, there exist gap regilns in the density of states of electrons between the boundaries of each Landau level.

Self-balancing resistance ratio bridge using a cryogenic current comparator

A cryogenic current comparator resistance bridge, developed to measure the resistance ratios of 1, 10, 100, and 6453.2 Omega against 1 Omega , is described. It is shown that the precision of the 1- Omega comparison is better than 0.01 p.p.m. This is attained by using an improved feedback system in the secondary current source. >

Hall Current Measurement under Strong Magnetic Fields for Silicon MOS Inversion Layers

Quantitative results of Hall conductivity σ x y in n -type silicon inversion layers have been obtained successfully by the use of the Hall current method. Results in the electron mobility dependence of the Landau level width are in good agreement with the theoretical prediction.

Electron localization in silicon inversion layers under strong magnetic fields

The magnetoconductivity σxx of the ground Landau level in n-channel Si(100) inversion layers in low mobility (μpeak = 3600 cm2V · s) and high mobility (μpeak = 12,000 cm2V · s) samples has been measured at temperatures T= 1.5–20 K under magnetic fields up to 150 kOe. Temperature and source-drain field dependences in the low mobility sample suggest the effect of local potentials is stronger than the electron-electron interactions. Temperature and sourcedrain field dependences in the high mobility sample suggest the influence of the electron-electron interaction is stronger than the local potentials in the sample.

Quantized Hall resistance measurements

The quantized Hall resistances, R/sub H/(4), of Si MOSFETs were measured at approximately=0.5 K in a magnetic field of 15 T. The value of R/sub H/(4) was determined in terms of the Commonwealth Scientific and Industrial Research Organization (CSIRO) realization of the SI ohm. A weighted mean of three determinations gave a value for the quantity R/sub H/(4) of (6453.203,36(52)) Omega /sub SI-NML/ which can also be expressed as 6453.2(1.000,000,52(8)) Omega /sub SI-NML/. This R/sub H/(4) value gives a value for h/e/sup 2/ which is about 0.3 p.p.m. larger than the value for h/e/sup 2/ derived from the anomalous moment of the electron, using the quantum electrodynamics (QED) theory. >

Activation Energies of the 1/3 and 2/3 Fractional Quantum Hall Effect in GaAs/AlxGa1-xAs Heterostructures

Activation energies of the diagonal resistivity ρ x x near the minima in the 1/3 and 2/3 fractional quantum Hall effect are determined in very high mobility GaAs/Al x Ga 1- x As ( x ≃0.3) heterostructures. Measurements of ρ x x and ρ x y are made at temperatures ranging from 1 K to 0.1 K in magnetic fields up to 15.5 T. The activation energies are 2.7 K and 0.89 K at the filling factor of a Landau level of 1/3 and 2/3, respectively. The former is in good agreement with theoretical predictions.

An improved Josephson potentiometer system for the measurement of the quantum Hall effect

Several improvements have been made on a Josephson potentiometer and superconducting quantum interference device (SQUID) galvanometer system previously reported. Results of the measurement of the quantized Hall resistance obtained by the use of this system are in agreement with those obtained by means of a conventional potentiometer system to 0.02 ± 0.08 ppm for silicon-MOSFET samples. A comparison of the Hall resistance between two different quantized values corresponding to h/4e2 and h/8e2, for a sample, has been made without an uncertainty associated with the linearity of voltage-ratio measurements. A discussion is presented in relation to completeness of the quantization.