Eizo Otsuka

Electron Scattering by Neutralized Acceptors in Germanium : I.Gallium and Indium

It is shown that the well-known Erginsoys formula for scattering of electrons by neutral impurity is not valid for the electron scattering by neutralized acceptors in germanium or silicon. An alternative formula based on the positron-hydrogen scattering picture is presented and compared with the cyclotron resonance observation of the electron scattering by gallium and indium atoms in germanium. From the temperature dependence of the scattering a unique determination of the effective Bohr radius of the neutral acceptor wave function is possible and the values of a ,* ca. 35A for gallium and 55A for indium have been obtained. In addition, a promising possibility of observing electron cyclotron resonance in highly doped p-type materials is pointed out, which is due to the smaller scattering cross section for acceptors than that for donors.

Galvanomagnetic Properties of n-Type InSb at Low Temperatures : II. Magnetic Field-Induced Metal-Nonmetal Transition

Experimental evidence for the magnetic field-induced metal-nonmetal transition in n–InSb has been obtained, under the magnetic fields up to 13.3 kOe, by systematically investigating the Hall coefficient and the transverse magnetoresistivity for the samples containing 2×10 14 –4×10 15 cm -3 of donors with nearly fixed compensation ratio K ∼0.5 at liquid helium temperatures. The donor concentration dependence of the critical magnetic field strength at the transition satisfactorily agrees with the theoretical prediction on the impurity band. The observed minimum metallic conductivity proves practically insensitive to magnetic field and increases with increasing density of localized centers, in accord with Motts concept of the metal-nonmetal transition in doped semiconductors.

Determination of Deformation Potential Constants from the Electron Cyclotron Resonance in Germanium and Silicon

Precise determinations of the deformation potential constants \(\varXi_{u}\) and \(\varXi_{d}\) of the conduction band edge are carried out at liquid helium temperature both for germanium and for silicon by means of electron cyclotron resonance. \(\varXi_{u}\) is determinable from the resonance intensity measurements under the application of uniaxial stress, while \(\varXi_{d}\) from the anisotropy of linewidth for pure specimens with the help of the already obtained value of \(\varXi_{u}\). The Herring-Vogt equation under the classical condition \(k_{\text{B}}T/\hbar\omega{>}1\) is used for deriving \(\varXi_{d}\). An extreme care must be taken if one uses the measured absolute linewidth to get \(\varXi_{u}\) and \(\varXi_{d}\). The obtained values are \(\varXi_{u}{=}19.3\pm 0.7\) eV and \(\varXi_{d}{=}-12.3{\pm}0.5\) eV for Ge, while \(\varXi_{u}{=}9.0{\pm}0.4\) eV and \(\varXi_{d}{=}-6.0{\pm}0.8\) eV for Si.

Cyclotron Resonance of Doped Silicon

Electron scattering and recombination studies through cyclotron resonance in doped silicon are carried out between 1.5 and 4.2°K. It is found that below 4.2°K the electron resonance linewidth for p -type silicon consists not only of scattering effect, but also of lifetime broadening. The latter can largely be eliminated on application of a strong uniaxial stress. So long as the scattering part is concerned, the observed features both for n -and for p -type materials are qualitatively explicable through the model of electron or positron scattering by a free hydrogen atom. Some discrepancies owing to the failure of the effective mass approach, however, are observed for all the dopants except for lithium. Analyses of temperature, stress and concentration dependence of electron lifetime in boron-doped silicon lead to the conclusion that the neutral boron impurities themselves are responsible for the carrier recombination.

Line-Width of Quantum Limit Cyclotron Resonance. I. Phonon Scatterings in Ge, Si, CdS and InSb

Studies of the Cyclotron Resonance Line-Width (CRLW) in the quantum limit have been made for phonon scatterings in basic semiconductors (Ge, Si, CdS and InSb). The acoustic deformation potential scattering has been examined for Ge and Si, while the acoustic piezo-electric scattering for CdS. The effect of the inelastic scattering is enhanced in the quantum limit. Furthermore, the spontaneous acoustic phonon emission is clearly affecting CRLW. Temperature dependences of CRLW for deformation potential and piezo-electric scatterings are similar to each other. Difference, however, arises in the magnetic field dependence. With regard to polar optical phonon scatterings, it has been confirmed for InSb that CRLW is dominated by the absorption part.

Galvanomagnetic Properties of n-Type InSb at Low Temperatures. I. Localization of Carriers and Metallic Impurity Conduction under Zero and Weak Magnetic Fields

The Hall coefficient and resistivity, under zero and weak magnetic fields, of n-InSb containing 1×10 13 –2×10 15 cm -3 of excess donors have been systematically investigated at liquid helium temperatures. By increasing compensating acceptors with a nearly fixed donor concentration ( N d ∼2×10 14 cm -3 , it is observed that the localization of the Hall carriers, or the metal-nonmetal transition, occurs at the excess donor concentration of ∼6×10 13 cm -3 (compensation ratio K ∼0.7) at 1.3 K. In the metallic range, the impurity concentration has been changed with a nearly fixed compensation ratio ( K ∼0.5), and it is confirmed that the impurity conduction (of metallic type) is recognized in the excess donor concentration range up to ∼4×10 14 cm -3 .

The Quadrupolar Effect in Alkali Halide Mixed Crystals

Using NaBr–NaCl mixed crystals, we have observed the quadrupolar effect on the nuclear resonance absorption line of Na. The minority halogen plays the role of “impurity” or “solute” as in the case of alloys treated by Bloembergen and Rowland. The satellites of Na in NaCl are affected when the solute Br comes at the third halogen site counted from Na site, where the field gradient then becomes q ∼10 21 cm -3 . From our analysis the antishielding factor λ for Na is given as ∼10. The asymmetric broadening of the central line due to the second order perturbation occurs when and only when the solute comes next to the Na nucleus. The specimen being a single crystal, the satellites of the second order arise at the definite positions depending upon the direction and strength of the external magnetic field. By measuring this shift of the resonance field, we see that the field gradients produced then at the Na site are nearly 1.4×10 23 cm -3 and 2.0×10 23 cm -3 , when Br - and Cl - are the solute ion, respectively....

Determination of Dislocation Densities Through Nuclear Resonance Studies

Studies of quadrupolar effects of mixed alkali halide on nuclear resonance previously reported for Na in NaCl–NaBr have been extended to Br in KBr–NaBr. Amplification factor for e Q q is thus derived and making use of this factor densities of dislocation are determined for a series of plastically deformed crystals of KBr. Although the effects of the screw and edge dislocations are additive for the broadening of the spectral line, their contributions to the net shift of the center of gravity of the line are in the opposite directions for H 0 //[100]. Hence the two kinds of dislocation are separable in density through the measurement of the breadth and asymmetry of the spectral line. Extrapolation to zero strain shows that for an undeformed crystal screw and edge dislocations are nearly balanced in number and their total density lies around 4×10 8 cm -2 . Linear Compression more favors the production of screw dislocations than that of edge dislocations and the density of each type dislocation increases quit...

Millimeter and Submillimeter Cyclotron Resonance Study of High-Purity ZnSe

We have observed for the first time the electron cyclotron resonance in a high quality ZnSe crystal, using both millimeter and submillimeter waves. We obtain an isotropic effective mass m*=0.145m0. From linewidth measurement it is found that the cyclotron mobility at 4.2 K exceeds 2.3×105 cm2/Vs. A strong anisotropy in absorption intensity has been observed in 35 GHz measurement.

Anisotropy of Nuclear Magnetic Resonance due to Crystal Dislocations

Using plastically deformed crystals of KI, the nuclear magnetic resonance of I 127 has been observed. The broadened signals of I 127 show distinct anisotropy as regards the direction of the external magnetic field. This anisotropy is interpreted to arise from the definite orientation of a crystal dislocation. The experimental results are analyzed in terms of the gradient-elastic tensor which has been introduced by Shulman-Wyluda-Anderson. It is concluded that densities of edge and screw dislocations are fairly well balanced and increase for a certain range almost linearly with degree of cold-working, in agreement with the previously reported result for KBr. Assuming the total dislocation density to be 10 9 cm -2 for ten percent deformation, we get | C 44 |∼8×10 4 statvolts/dyne and its one-third for | C 11 |. Comparison with the result for KBr shows that the amplification factor of e Q q is greater than 50 for I 127 in KI.