摘要:

A study of the de Haas‐van Alphen oscillations in the magnetic susceptibility has been carried out inp‐type PbTe andn‐type PbS. Measurements have been made on oriented single crystal samples with carrier concentrations of the order of 1018/cm3in pulsed magnetic fields up to 125 kgauss. The results forp‐type PbTe indicate that the valence bands have a maximum atk=0, and four equivalent maxima at the {111} Brillouin zone faces. The ⟨111⟩ ellipsoids have a longitudinal mass to transverse mass ratio of 6.4±0.3. From the temperature dependence of the amplitude of the oscillations we obtain a value of 0.043±0.006m0for the transverse effective mass. The data indicate that the (000) maximum and the (111) maxima lie within 0.002±0.002 ev of each other. The data also indicate an effective broadening temperature of about 8°K which is attributed to inhomogeneities in the carrier concentrations in the samples investigated. Preliminary results onn‐type PbS show a single isotropic Fermi surface cross section with a cyclotron mass of 0.14±0.04m0. The direct and indirect optical interband transitions are discussed in the light of these results.

ISSN:0021-8979    

DOI:10.1063/1.1777037

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Oscillatory behavior of the transverse magnetoresistance has been used to investigate the conduction band structure of PbTe. From the oscillatory periods, it is established that the minima in the conduction band consist of four equivalent ⟨111⟩ prolate ellipsoids with a mass anisotropy of approximately 5.5 and located at the Brillouin zone edge. The decay of the oscillation amplitudes with temperature yields a transverse ellipsoid mass ofmT*=(0.030±0.005)m0. High field oscillations have been detected that point to the existence of a second band located at the center of the zone, having a mass of about 0.08m0, and lying within ±0.002 ev of the ellipsoid minima. The phase of the oscillations suggests that spin splitting of the Landau levels may be quite large in PbTe.

ISSN:0021-8979    

DOI:10.1063/1.1777038

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The magnetic field dependence of the Hall coefficient at 296° and 77°K, and the temperature dependence of the weak‐field Hall coefficient and the resistivity between 296° and 77°K were studied in single‐crystal samples ofp‐type PbTe having carrier concentrations ranging from 4.9×1017to 1.7×1019per cm3. The Hall data at 77°K are quantitatively consistent with magnetoresistance data which have previously established the presence of ⟨111⟩ ellipsoids in the valence band. They are not consistent with a low‐temperature two‐band model, proposed by Stiles from de Haas‐van Alphen data at 4.2°K, unless the band edges lie at approximately the same energy (as Stiles found) and unless the carrier mobilities in the two bands are nearly alike. On the other hand, both the Hall and resistivity data above about 150°K do exhibit two‐carrier effects suggesting the presence of a lower mobility band at an energy about 0.1 ev below those bands which are occupied at low temperatures.

ISSN:0021-8979    

DOI:10.1063/1.1777039

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Rotation of a large magnetic field (∼60 kgauss) in a plane perpendicular to the direction of junction current in PbTe tunnel diodes produces a periodic behavior of this current. Diodes in which the junction current flow is along the [100], [110], or [111] crystallographic axis have been investigated. The observed anisotropies are consistent with a crystal with cubic symmetry whose constant energy surfaces inkspace are ellipsoids of revolution oriented along the ⟨111⟩ crystalline axes. The magnetotunneling results are interpreted in terms of the effective motion of each ellipsoidal valley as the magnetic field is increased, valleys oriented at different angles to the electric field contributing with different weights to the tunneling current. Quantitative comparison awaits theory. Heavier mass bands close in energy to these ellipsoids, although unimportant by themselves in tunneling, may be necessary to explain the apparent position of the Fermi level with respect to the band edges. The excess current has the same anisotropy as the tunneling current; however, the thermal current does not show this anisotropy and therefore must be of different origin. Hump current, which was observed in two diodes, disappeared in magnetic fields above 3 kgauss.

ISSN:0021-8979    

DOI:10.1063/1.1777040

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The electrical conductivity and optical absorption data for many compounds of the transition metals suggest that there is a trend from ionic insulators, to metals, to covalent semiconductors as the overlap of atomic orbitals is increased. In this paper it is shown that a correlation exists between the electrical behavior of insulators and metals and the magnitude of the overlap integralsS(d&egr;d&egr;) andS(d&egr;p&pgr;).

ISSN:0021-8979    

DOI:10.1063/1.1777041

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

This paper reviews the work which has been carried out in these Laboratories during the past two years on single crystals of bismuth telluride and its alloys.The combination of experiments on Faraday rotation with those performed previously on galvanomagnetic effects has established that there are 3‐ and 6‐valley band structures associated withp‐ andn‐type Bi2Te3, respectively. However, observations of the anisotropy ratio for the electrical conductivity and of the galvanomagnetic coefficients for heavily dopedn‐type material have shown that the shape of the equal‐energy surfaces is dependent on carrier concentration. Similar conclusions have been drawn from the behavior of the Seebeck coefficient at low temperatures.Measurements on Bi2Te3at low temperatures and on alloys of Bi2Te3have shown that the lattice thermal conductivity is particularly sensitive to the substitution of atoms of I, Se, or S for those of Te. It has also been shown that the anisotropy ratio for the lattice thermal conductivity is almost the same for the alloys as for pure Bi2Te3.

ISSN:0021-8979    

DOI:10.1063/1.1777042

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

It is shown that the simple ``hopping model'' for the transport processes of mixed valency semiconductors is inadequate for impurity concentrations [similar or greaterthan]1%. In particular, it is necessary to redefine (1) the number of free charge carriers, and (2) the density of available states because of the dominant role played by the impurities in the high concentration range.

ISSN:0021-8979    

DOI:10.1063/1.1777043

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The low‐lying eigenstates of the ``large polarons'' have been calculated by several authors for arbitrary strengths of the electron lattice interaction &agr;. However, if &agr; > 1 the large polaron picture becomes questionable, since for finite temperatures the polaron eigenstates may be strongly affected by the presence of thermal phonons; then a new approach to the polaron theory is applicable which takes into account the atomicity of the lattice and the presence of thermal phonons and which results in the ``small polaron'' picture. The eigenstates of small polarons depend onT. If the eigenstates form a band, the bandwidth is a function ofT, and the eigenstates near the band extremum can be expressed in terms of aT‐dependent effective mass. From measurements of the high‐ and low‐frequency dielectric constants, of the temperature dependence of the Seebeck coefficient, and of the electronic mobility, it appears that the eigenstates of the electronic charge carriers in Ce&sngbnd;S semiconductors may be adequately described by the small polaron picture.

ISSN:0021-8979    

DOI:10.1063/1.1777044

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A review is made of the work on reduced and ``doped'' rutile performed since the appearance of Grant's survey article in the Reviews of Modern Physics (1958). Measurements of electrical and optical properties, and of electron spin resonance spectra are discussed. A model of electronic bound states and conduction levels is suggested that is compatible with the results of these experiments. There is strong evidence that the defects in reduced rutile are interstitial Ti3+ions. At very low temperatures, nearly all electrons are self‐trapped on cation sites (polarons). As the temperature increases, some of these trapped electrons will be excited into the conduction band. The activation energy for this process is approximately 0.007 ev below 50°K, and about one order of magnitude higher around room temperature. It is concluded that conduction takes place in a narrow 3dband associated with Ti ions; the effective mass at the bottom of this band is ∼25m0. If one assumes that the polaron binding energy can be described with a hydrogenic model, one calculates an effective dielectric constant close to the static value. This result is at variance with the commonly accepted ideas concerning electron lattice coupling.

ISSN:0021-8979    

DOI:10.1063/1.1777045

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A Heitler‐London approach to electrical conductivity is proposed in order to discuss conduction in semiconductors with incompletedshells, in which the mobility of carriers is very low. The physical conditions which make the hopping motion of the electrons predominant is examined in detail.

ISSN:0021-8979    

DOI:10.1063/1.1777046

出版商:AIP    

年代:1961

数据来源: AIP