Nobuo Kotera

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.

Noise and electrical transport properties of polycrystalline InSb thin films

Both noise and electrical transport properties of polycrystalline InSb thin films are measured and analyzed for the same potential model. Films are prepared by evaporation upon sputtered SiO2 glass and annealed in an Ar atmosphere. Films are inhomogeneously compensated and show what appears to be p‐ and n‐type conduction at low temperatures. It is found that the n‐type films actually contain p‐n junctions because the measured barrier heights reach the energy of the band gap. Between 150 and 77°K, low conducting sheets along grain boundaries with notch‐type barriers exist. Current noise of 1/f type observed at room temperature is well correlated with this notch‐type barrier. A higher notch‐type barrier leads to lower mobility as well as higher noise voltage. This indicates that the noise originates in the bulk effect of the films.

Differential Negative Resistance of n‐Type Inversion Layer in Silicon MOS Field‐Effect Transistor

A new type of voltage‐controlled differential‐negative‐resistance effect was observed in an n‐type surface inversion layer of a silicon MOS field‐effect transistor with a very high mobility of 104 cm2/V sec at low temperatures.

Microzone Recrystallization of InSb Thin Films for Hall Effect Magnetic Heads

A new processing method is proposed for fabricating indium antimonide thin film Hall elements on ferrite substrates applicable to high singal-to-noise ratio Hall effect magnetic heads. The procedures include (1) coating the substrate with a thin glass layer containing 12 mol% alumina, then evaporating InSb film on it, (2) microzone-recrystallization of the film in a helium atmosphere containing ~300 ppm oxygen, and (3) lapping the film to obtain a desired thickness (2 µm) and smooth surface. The film thus formed, having the grain size of ~3 mm×0.5 mm and dislocation density of ~107 cm-2, shows electron mobility of 60,000 cm2/Vs, Hall coefficient of 350 cm3/C at 300 K (comparable to those of the purest single crystal) and remarkably low current noise in the audio frequency range.

Transverse 1/f noise in InSb thin films and the signal‐to‐noise ratio of related Hall elements

Transverse 1/f noise in approximately 2‐μm‐thick InSb thin films is investigated experimentally at room temperature. Linear dependence of noise voltage on dc bias current is shown quantitatively. The noise intensity is inversely proportional to the number of conduction electrons in the bulk. The temperature rise of specimens due to Joule heating does not affect the noise intensity coefficient. The coefficient differs from sample to sample, which is reduced by the heat treatment of specimens, but is independent of the doped impurity concentration. As a result, the signal‐to‐noise ratio of related Hall elements is formulated for the first time for audio magnetic heads applications. The signal‐to‐noise ratio is nearly 80 dB for a 10‐G magnetic field in the audio frequency range.

Measurement using a current-axis-independent Josephson sampler

We have improved measurement of the current‐axis‐independent Josephson sampler. We use a new chopping detection circuit in the feedback system for sampling point control. Two channels of the sampling head are utilized to cancel drift in the time base. Drift is about 3 ps. We have measured the output of a short pulse generating circuit and obtained a transition duration of 15 ps.

Two-Dimensional Impurity States in an n-Type Inversion Layer of Silicon

Shallow impurity states associated with the electric subband in the n-type surface inversion layers have clearly been observed on the Si (100) surface. Measurements of the conductivity and the transconductance have been made at temperatures from 4.2 to 300 K, especially at low gate voltages near the threshold for the surface inversion, whose values are given in terms of effective mobility as well as field effect mobility. When the surface carrier density is less than 5×1010 cm−2, the surface conductance varies as exp(−ea/kT) and the activation energy ea has been determined to be 1.2 meV. In this case, the peak of the transconductance, the differential conductance with respect to the gate voltage, disappears at 12 K, which agrees with the activation energy. When the surface carrier density is more than 1×1011 cm−2, the effective mobility is independent of temperature below 20 K and the electron statistics might be degenerate.

Transport Properties of Electrons in Inverted InSb Surface

Measurements were made of electrical transport properties of the electrons in inversion layers produced in metal–oxide–p-InSb structure at 4.2 K. One possible interpretation is reported. Surface conductance Δσs due to inversion layers as a function of gate voltage VG was measured in magnetic field H up to 14 kOe. The curves of Δσs in the magnetic field normal to the surface had plateaus. The width of the plateaus were enlarged on the positive side of VG with increasing magnetic field. While Δσs in the magnetic field normal to the surface decreased ordinarily with increasing H, Δσs in the field parallel to the surface plane tended to a finite value. Values of Δσs showed two peaks when the direction of the magnetic field was rotated in a plane normal to the surface current. The width of the peak was narrower in the case of magnetic fields where electrons were pushed toward the oxide–InSb interface rather than into the bulk of the InSb. These characteristics may be interpreted as follows: The effect of quant...

Reply to ’’Comment on ’Transverse 1/f noise in InSb thin films and the signal‐to‐noise ratio of related Hall elements’ ’’

Noise formula describing the 1/f noise in InSb films is pointed out. The noise‐intensity coefficient K is introduced as a variable depending on film‐preparation methods. Experimentally, K2 changes by two orders of magnitude. However, existing noise calculations show that K2 should remain constant except for a dimension factor. Therefore, the experimental results cannot be explained by the existing theory.

Energy dependence of electron effective mass and effect of wave function confinement in a nanoscale In0.53Ga0.47As/In0.52Al0.48As quantum well

The effective mass in the conduction band was analyzed as a function of the kinetic energy in a 5–20 nm-thick In0.53Ga0.47As/In0.52Al0.48As quantum well (QW). An increase in the effective mass caused by wave function confinement in the QW, which was previously proposed theoretically, was not found to be present in this material under the framework of the energy effective mass. In the direction normal to the QW plane, the mass determined by the interband optical transition at 100-300 K fitted well with the calculated result based on Kanes bulk band theory. In a direction parallel to the QW plane, the cyclotron resonance energy at less than 70 T and the magneto photoluminescence energy at less than 13 T fitted with the calculated result to within an error range of ±2 meV. In the analysis of the magneto-photoluminescence at 1.4 K, the bandgap renormalization was determined and large new peaks appeared above 8 T, possibly because of the interaction of the magneto-exciton states with the ground-state zero-dimensional Landau level.The effective mass in the conduction band was analyzed as a function of the kinetic energy in a 5–20 nm-thick In0.53Ga0.47As/In0.52Al0.48As quantum well (QW). An increase in the effective mass caused by wave function confinement in the QW, which was previously proposed theoretically, was not found to be present in this material under the framework of the energy effective mass. In the direction normal to the QW plane, the mass determined by the interband optical transition at 100-300 K fitted well with the calculated result based on Kanes bulk band theory. In a direction parallel to the QW plane, the cyclotron resonance energy at less than 70 T and the magneto photoluminescence energy at less than 13 T fitted with the calculated result to within an error range of ±2 meV. In the analysis of the magneto-photoluminescence at 1.4 K, the bandgap renormalization was determined and large new peaks appeared above 8 T, possibly because of the interaction of the magneto-exciton states with the ground-state zero-dim...