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Electron Tunneling Spectroscopic Analysis of Narrow-Gap Semiconductor Antimony Telluride and Semimetal Antimony

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Title: Electron Tunneling Spectroscopic Analysis of Narrow-Gap Semiconductor Antimony Telluride and Semimetal Antimony
Other Titles: ナローギャップ半導体Sb2Te3ならびに半金属Sbの電子トンネル分光解析
Authors: Hatta, Eiji1 Browse this author →KAKEN DB
Authors(alt): 八田, 英嗣1
Issue Date: 30-Sep-1997
Abstract: In this work tunneling studies on an antimony telluride, V-VI narrow-gap semiconductor (NGS), and an antimony, an element of the compound semiconductor, are described and discussed. Tunnel junctions of the types Au-Sb2Te3-Al and Al-Al oxide-Sb were prepared. A clean surface, an important condition for tunneling experiments, was produced by the layer-by-layer deposition in a high vacuum (<5×10-7 Torr) without breaking the vacuum. Sb2Te3 films were prepared by the flash evaporation of antimony telluride pellets. A rejection-selection filter network suitable for the detailed study of the first and second derivatives of the current-voltage characteristics of tunnel junctions was constructed. The uniqueness of the network lies in its low noise and in its applicability for wide range of resistance of the tunnel junctions (1 Ω - 10 kΩ). The filter network tunneling spectrometer is described in detail. A narrow width conductance peak at zero bias voltage with a symmetric undershoot structure is found in Au-Sb2Te3-Al tunnel junctions. Except for the voltage symmetric undershoot structure, this behavior is found to be well described by a tunnel equation where a nonparabolic E - k dispersion relation of Kane's type is involved. In this model, analytic continuation of the E - k relation from the conduction- and valence bands at the middle of the energy gap is successfuliy carried out if the both band edge effective masses are the same. From this analysis, it is shown that the Fermi level locates just above the valence band edge in this material. The origin for undershoot structure is discussed. It is particularly emphasized that this analysis is essential for tunneling through a narrow-gap semiconductor whose Fermi level locates near the valence band edge. It is also noted that the two-band analysis must be necessarily carried out for tunneling through a solid barrier with conduction- and valence bands. Electron tunneling experiments have been carried out to investigate the confumed anisotropy of Fermi surfaces and phonons in a semimetal antimony. Depending upon the texturization of antimony films, the definite change in shape of tunneling conductance is observed. In addition to the intervalley acoustic and optical phonon peaks, the intravalley acoustic phonon peak becomes observed in the second derivative curve dependent upon the exposed crystal faces. This intravalley acoustic phonon peak has never been observed in Raman spectra and neutron scattering experiments. As for the intervalley acoustic and optical phonon peaks, the half-width of these peaks becomes decreased as the change of the exposed crystal faces. This is the first observation of the anisotropy of Fermi surfaces and phonons in tunneling spectroscopy. Moreover this is the first observation of the intravalley acoustic phonon peak in tunneling spectroscopy. The overtone phonon peak exhibits an asymmetric structure in contrast to that of the Raman spectrum. This might be due to the difference of coupling functions. Electron tunneling measurements have been performed to study the one-particle density of states in inhomogeneous Sb films. A conductance minimum is observed at zero bias and the result can be well described in terms of the theory of electron-electron interaction in weakly disordered metals. On the other hand, at higher voltages the background conductance curve exhibits roughly an asymmetric parabola, as is typical in a metalinsulator-metal (and not semimetal) tunnel junction. The feature of band structure in the semimetal disappears completely. This result indicates that an inhomogeneous Sb film constitutes a metallic, degenerate electron gas system at the interface of the junction. A metastable metallic phase of Sb may be stabilized due to a higher disorder. This is the first evidence of the disorder induced semimetal-metal transition.
Conffering University: 北海道大学
Degree Report Number: 乙第5228号
Degree Level: 博士
Degree Discipline: 工学
Type: theses (doctoral)
Appears in Collections:学位論文 (Theses) > 博士 (工学)

Submitter: 八田 英嗣

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