摘要:

A detailed analysis of Hall coefficient data obtained at temperatures between 77° and 350°K has been made for HgSe and HgSe0.5Te0.5samples containing excess donor concentrations up to 1019cm−3. On the basis of previous magnetoresistance, Seebeck coefficient, and reflectivity data, a spherically symmetric non‐quadratic conduction band exhibiting the &egr;(k) dependence described by Kane was adopted in making the analysis. Calculations based on a conventional two‐band model failed to give quantitative agreement with experiment, but good agreement was obtained on the basis of a model in which the conduction band and one valence band overlap in energy. Therefore the materials are semimetals rather than semiconductors. The best fit to the data was obtained with an overlap energy of 0.07 ev for both HgSe and HgSe0.5Te0.5, with hole density‐of‐states masses of 0.17m0and 0.30m0, respectively. With increasing carrier concentration, the optical absorption edge for heavily doped HgSe exhibits a shift to higher energies which is characteristic ofn‐type materials with low electron effective masses. Qualitatively, the optical data are consistent with a semimetal band model rather than with a semiconductor model, since the interband absorption edge apparently occurs at photon energies less than the Fermi energy.

ISSN:0021-8979    

DOI:10.1063/1.1777057

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A semi‐empirical theory of exciton structure in the presence of an external magnetic field developed from Dresselhaus' effective mass approximation [G. Dresselhaus, J. Phys. Chem. Solids1, 15 (1956)] has been used to obtain the band parameters atK=0, 0, 0 of CdSe from observed exciton spectra. The theory has been approximated to the case of uniaxial crystals of small anisotropy by the assumption that the effective mass tensor for both the hole and the electron is diagonal, the remaininganisotropy is cylindrical and small and that the anisotropy in the dielectric constant is also cylindrical and small. The exciton spectra of CdSe has been observed and identified by optical reflection, absorption, and Zeeman structure at 1.8°K. The reflection and absorption spectra indicate the presence of two nonoverlapping exciton series. From observed optical selection rules, the conduction band is identified as having &Ggr;7symmetry. The two series correspond to the &Ggr;9−&Ggr;7valence band crystal field splitting of approximately 200 cm−1. A third series, at higher energies, has been observed in absorption corresponding to a &Ggr;7valence band state split by spin‐orbit effects from the other two states by approximately 3490 cm−1. Then1= 1, 2, 3, and 4 states of the first, &Ggr;9, series, then2= 1 and 2 states of the second (first &Ggr;7) series, and then3= 1 state of the third (second &Ggr;7) series have been observed and identified in absorption. The series limit of the first series, corresponding to the band gap, has been measured to be 14 850 cm−1. The band parameters have been obtained by comparing theory and experiment. The effect of the finite photon momentum has been observed through changes in the Zeeman structure of then1= 2,Pstates upon 180° rotation of the magnetic field in the plane perpendicular to the crystalCaxis.

ISSN:0021-8979    

DOI:10.1063/1.1777058

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The theoretical effects of a finite slope condition band crossing on the direct exciton energy levels of wurtzite compounds is investigated. The lack of an experimental confirmation of these effects places an upper limit of about 10−10ev‐cm on the slope of the conduction band atk= 0 in CdS, and a slightly larger limit in CdSe. Theoretical estimates of these slopes are also calculated. Another possible method of observing the magnetic effects due to the nonzero wave vector of the excitons is noted. The striking increase of the exciton oscillator strength in CdSe in a magnetic field is attributed to the magnetic compression of the excitons. A brief comparison of experimental energy band parameters for CdS and CdSe is given.

ISSN:0021-8979    

DOI:10.1063/1.1777059

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The absorption coefficient for polarized light at photon energies less than that of the lowest lying direct exciton was measured for single crystals of ZnO at temperatures ranging from 20° to 200°K. Analysis of the results shows that the absorption is in agreement with that calculated for a process involving the simultaneous creation of an exciton and absorption of a phonon, both particles having a small wave vector. This agreement provides evidence that the absolute minimum of the conduction band cannot lie lower than the lowest lying direct exciton level, and, therefore, that the absolute minimum probably occurs at the center of the Brillouin zone. Values for the hole and electron masses were estimated from the analysis.

ISSN:0021-8979    

DOI:10.1063/1.1777060

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Piezoelectric scattering of conduction electrons by acoustical phonons is discussed for ZnO and CdS, and approximate values of the mobilities determined by this mechanism alone are derived. The phonon drag contribution to the Seebeck effect in ZnO is assumed to arise from crystal‐momentum exchange between electrons and acoustical phonons by way of the piezoelectric interaction alone. Comparison of the results of this assumption with the data has led to the discovery of strong piezoelectric phonon scattering from neutral donor states. These two piezoelectric scattering mechanisms and an effective electron mass of about 0.32m, derived from other experiments, provide a model for phonon drag in ZnO which agrees with the temperature dependence and ``impurity'' dependence of the data and gives the correct magnitude of the effect to within the uncertainties of the approximations employed.

ISSN:0021-8979    

DOI:10.1063/1.1777061

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The bands of infrared absorption in hexagonal cadmium sulfide have been studied over a wide range of temperatures and are assigned to double‐phonon processes. An analysis of these absorption peaks on the basis of four frequencies is proposed. The temperature‐dependence of the location and intensity of these bands give indications upon the anharmonic parameter and Gru¨neisen constant of the crystal. Anharmonic forces are shown to be responsible for the coupling between normal vibrational modes.

ISSN:0021-8979    

DOI:10.1063/1.1777062

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A single exciton peak may be seen in the reflection spectrum of CdTe, a semiconductor with the cubic zinc‐blende structure. Some properties of this exciton and of the associated fluorescent phenomena are described. Under uniaxial compressive stress, the single exciton peak splits into two peaks corresponding to the splitting of theJ=32valence band. The movement of the peaks as a function of stress has been determined for four directions of stress in the (110) plane. Within experimental error, the splittings are identical for a given stress applied in any direction. Thus, although the material is elastically anisotropic, the splitting may be described by one rather than two deformation potentials. These conclusions are consistent with the polarization properties of the exciton transitions. The polarization properties also show that under compressive stress theMJ=±½ band moves ``up'' and theMJ=±32band moves ``down.''

ISSN:0021-8979    

DOI:10.1063/1.1777063

出版商:AIP    

年代:1961

数据来源: AIP