The thermoelectric properties of systems in the form of superlattices have been studied. First, the electrical and thermal conductivities, the thermopowers, and the figures of merit of superlattice structures are given in terms of the bulk parameters of the two constituent materials for conduction both parallel and perpendicular to the superlattice axis. Second, systems in which the layers of one of the materials become sufTiciently thin that their electronic properties become effectively those of a twodimensional quantum well are considered. Numerical calculations are given for such systems with Bi&Te3 quantum wells separated by barriers having the parameters of bulk Pb075Sno»Te. It is shown that heat and electronic conduction through the barriers has a pronounced effect on the thermoelectric properties of the superlattice and that the figure of merit is decreased substantially for finite barrier thicknesses.
The shallow acceptor states in gallium arsenide have been studied by far-infrared Fourier transform spectroscopy. The energy level structure observed in photoconductivity is compared with the predictions of recent acceptor state theory and the agreement is found to be generally good. The groundstate ionisation energies are found to be 26.9 meV (carbon), 28.7 meV (magnesium), 30.6 meV (zinc) and 34.8 meV (silicon). The general features of the GaAs spectra are also compared with results previously obtained for Ge by Jones and Fisher (1965) for InSb by Kaplan (1973) and deep manganese acceptors in GaAs by Chapman and Hutchinson (1967). There is strong similarity between GaAs and the other materials. This similarity extends to the Zeeman spectra and is exploited in interpreting the Zeeman components observed in GaAs in terms of theoretical predictions.
A pseudopotential energy band calculation is carried out for a hypothetical crystal which corresponds to Cd,P, and Zn,P,. From these results, the conduction band effective masses as well as the interband transition assignments associated with the optical reflectivity peaks are deduced. The temperature dependence of the energy gap for these materials is estimated and dE,/dT is shown to be negative.Mit der Pseudopotential-Methode wird eine Energiebandberechnung fur einen hypothetischen Kristall, der C$P, und Zn,P, entspricht, durchgefuhrt. Mit diesen Ergebnissen werden die effektiven Massen des Leitungsbandes sowie die Zuordnungen der Interbandiibergltnge zu den Maxima des optischen Reflexionsvermogens hergeleitet. Die Temperaturabhangigkeit der Energielucke wird fur diese Stoffe abgeschltzt und gezeigt, daS dE,,dT negativ ist.
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