Oscillatory thickness dependences of the electrical conductivity, Hall coefficient, charge carrier mobility, and Seebeck coefficient were obtained at room temperature for n-type thin Bi films (d=3–300 nm) fabricated by the thermal evaporation of a bismuth crystal in a vacuum and deposition on mica substrates at 380 K. We attribute this oscillatory behavior to quantum-size effects, which are observable when the electron mean-free path and Fermi wave length exceed the film thickness d.

Quantum-size effects in n-type bismuth thin films

The thickness and temperature dependences of electrical and thermal transport coefficients (e.g. electrical conductivity, thermoelectric power, thermal conductivity) of Bi1–xSbx films are described by a non-degenerated two-band model, considering the anisotropic elliptical band structure (many-valley model) of bulk Bi1–xSbx. The transport coefficients are measured in the temperature range 80 to 400 K on films with thicknesses 20 to 400 nm and the results are interpreted and discussed using the deduced relations.



Die Schichtdicken- und Temperatura bhangigkeit elektrischer und thermischer Transportkoeffi-zienten (z. B. der elektrischen Leitfahigkeit, der Thermokraft, der Warmeleitfahigkeit) von Bi1–xSbx-Schichten wird im Rahmen eines nicht entarteten Zweiband-Modells unter Berucksichtigung der anisotropen elliptischen Bandstruktur (many valley model) von massivem Bi1–xSbx beschrieben. Die Transportkoeff izienten werden im Temperaturbereich 80 bis 400 K an Schichten von 20 bis 400 nm Dicke gemessen, und die Ergebnisse werden mit den abgeleiteten Beziehungen interpretiert und diskutiert.

Temperature and thickness dependence of electrical and thermal transport coefficients of Bi1–xSbx films in an anisotropic, non-degenerate two-band model

Influence de la taille des grains et de l'onde de de broglie sur les propriétés de transport des couches minces de bismuth

Structure and properties of thin films.

Infrared (IR) detectors for the long-wave infrared range (LWIR) based on nanostructured thermocouples exhibit response times in the order of picoseconds and will open new areas of applications in THz broadband communication systems We show experimental evidence for a nonzero relative Seebeck coefficient between the narrow and the wide wire segments of single-material thermocouples, and we investigate the thermal dynamics of nano-thermocouples for a substrate heated by a nanostructured thermocouple patch Due to its low thermal capacity a mesoscopic thermocouple is an extremely fast square-law detector with cutoff frequencies up to several hundred GHz

A Nanostructured Long-Wave Infrared Range Thermocouple Detector

Anomalous behaviour of the thermoelectric power of thin Bi films has been observed and the results are consistent with those anticipated, based on both quantum and classical size effects in scattering. Mayer's theory relating thermoelectric power to film thickness can be applied to the present results provided that the bulk conduction electron mean free path is used for calculations of the thermoelectric power of thick specimens and that the conduction electron de Broglie wavelength is used for thin specimens.

D. D. Thornburg

Papers

Quantum and classical size effects in the thermoelectric power of thin bismuth films