Ryozo Yoshizaki

Conduction Band Structure of Tellurium

The structure of conduction band edge of tellurium was investigated experimentally. The interband magneto-absorption was measured and the two series of the absorption lines were observed for H // c . The magnetic field dependence of the peaks for H ⊥ c was more complicated reflecting the valence band structure. The conduction band structure was derived theoretically with the effective Hamiltonian method, and it indicated that the k -linear terms play an important role, particularly in the appearance of the above two series. The comparison of theoretical and experimental results yielded determination of the band parameters, which reproduce well the experimental results. As a result, it was found that the conduction band consists of two ellipsoids with effective masses at the minima m ⊥ =0.104 m 0 , m // =0.070 m 0 and with g // =-9.86, | g ⊥ |=1.9. The binding energy of an exciton is calculated to be 0.69 meV and the exciton band has the double minimum, reflecting the large k -linear term in the valence band,

Far-Infrared Cyclotron Resonance in p-Type Tellurium

Cyclotron resonance absorptions of p -type tellurium were investigated at liquid helium temperatures in the far-infrared region from 120µm to 400 µm under the magnetic field up to 92 kOe. The CR transition energies were measured as a function of the magnetic field which was applied parallel to the three main crystal axes of tellurium, c -axis, binary and bisectrix. Fairly good agreements were obtained between the present experiments and the theoretical calculations made by Nakao, Doi and Kamimura (J. Phys. Soc. Japan 30 (1971) 1400. A fine structure was observed in the CR transition peak for H // c -axis, and the relative intensities of the fine structure changed with lowering the temperatures. This fact is possibly due to the unequal spacing of the transition energies along k z -axis between the Landau levels n =0 and 1. The impurity effects in the CR transitions were also measured for the antimony doped specimens with various carrier concentrations. It was found that the binding energy of the impurity s...

Infrared absorption by interband transition of holes in tellurium

Abstract The infrared absorption in tellurium single crystals due to the intervalence band transition of holes was investigated at liquid helium temperatures. A broad absorption band was newly found around 150 meV, besides the main absorption peaks at 126.0 and 128.6 meV. The results can be interpreted by using the model of the dumb bell shaped energy surface on the valence band of tellirium.

Impurity effects in far-infrared cyclotron resonance in p-type tellurium

Abstract Far-infrared cyclotron resonance absorptions and absorptions due to holes in impurity levels were observed in single crystals of p -type tellurium containing holes from 10 14 ∼ 10 16 cm −3 at 4.2°K. Identifications of the cyclotron resonance line positions are made and a possible explanation of the impurity cyclotron resonance is presented.

Magnetization Measurements of the Second Stage NiCl2-Graphite Intercalation Compound

We have investigated the induced ( M ) and residual ( M r ) magnetizations in the 2nd stage NiCl 2 -graphite intercalation compound at 4.2 to 300 K in the fields of 0.1 to 4.5×10 4 Oe with using the well-staged single crystal samples. Two successive magnetic phase transitions have been observed at T c1 =17.5 K and T cu =22.0 K. Above T cu the compound is paramagnetic with θ=70±1 K and µ eff =3.29 µ B . In the intermediate phase ( T c1 T cu ) to 2.0( T 10 Oe. These results suggest the existence of an ordered state at...

Far infrared absorption by acceptor states in tellurium

Abstract Transmission spectra of slightly antimony-doped tellurium were measured at 2K. Absorptions due to transitions of holes from the acceptor ground state to the excited state and to the valence band were observed. Reflecting the double-maximum structure of the valence band, the ground state splits into two levels, the binding energies of which are found to be 1.31 and 1.47 meV, respectively.

Uniaxial Stress Effect of Magneto-Optical Properties of HgTe

The (varGamma_{8})-(varGamma_{8}) interband magneto-absorptions in HgTe were measured using two far-infrared lasers (118 µm and 337 µm) under a uniaxial compressional stress.The stress was applied parallel to the magnetic field and to each of the principal crystallographic directions [001] and [111]. The experimental results show that the level inversion occurs between the lowest Landau levels of the conduction and the valence band by increasing the magnetic field for the case of the compressional stress. The observed resonance peaks were analyzed by using the effective mass theory. The shear deformation potentials of the (varGamma_{8}) bands have been obtained as D u =1.9±0.6 eV and D u =1.8±0.2 eV.

The Microwave Harmonic Generation in Semiconductors at Low Temperatures. I. Germanium

The microwave harmonic generation in n -type germanium is observed at liquid helium temperatures and it is found that the third harmonic generation (THG) shows the resonance behavior when the magnetic field is changed. The experimental results on the conversion efficiency, anisotropic behavior of the peaks, donor concentration dependence and the input power dependence of the THG are described. It is shown from these characteristics that the resonance type THG arises from the multi-photon resonance of electrons trapped in very shallow impurity states. A model is proposed that such impurity states are the states associated with the donor negative ion ( D - ), and the anisotropic behavior of the resonance field is reasonably interpreted in terms of the orbital Zeemann effect of the D - states.

Magnetic sub-band structure of HgTe under uniaxial stress

Abstract The magnetic sub-band structure of HgTe is calculated for the strain-splitting Γ8 bands, and the lowest Landau levels of the conduction and valence bands at kH = 0 are shown to cross each other as the magnetic field is increased. It is demonstrated that the crossing means the band inversion for the case of the compressional stress and the semimetal—semiconductor transition for the case of the tensile stress.

Transverse magnetoresistance and Hall effect in p-type tellurium in strong magnetic fields

Abstract Galvanomagnetic effects in tellurium with carrier concentrations ranges from 1014 ∽7×1015 cm-3 were measured at liquid helium temperatures in intense magnetic fields up to 90 kOe. In slightly doped crystals, whose carrier concentrations were about 3 ∽ 7 × 1015 cm-3, the magnetic field dependences of the Hall coefficient and the transverse magnetoresistance were found to be different from those in purer crystals. The results can be explained by assuming the existence of an impurity band and by taking into account the complicated structure of the Landau levels.