No abstract

No abstract

No abstract

Cyclotron resonance of electrons and holes has been observed in tellurium single crystals a t 24 and 70 GHz and at liquid helium temperatures. In pure specimens and a t low temperatures the surfaces of constant energy for the holes are well described by 4 prolate ellipsoids of revolution about the c-axis located near the Brillouin Zone corners. At higher hole energies produced by thermal or optical excitation or by heavily doping the crystals, pairs of t.hese ellipsoidal surfaces degenerate into dumbbell-shaped surfaces of revolution. The observed isotropic resonance of high mass electrons (m* = 0.75 mo) suggests a n indirect gap at low temperatures.Nous avons observe la resonance cyclotron des electrons et des trous dans le tellure monocristallin ii 24 e t 70 GHz et B 1.3 OK. Aux tempkratures basses dans les specimens purs un modhle B quatre ellipsoides de rbvolution situbs au voisinage des coins de la z h e de Brillouin represente les surfaces d'energie constante de la bande de valence. Aux energies plus elevkes, atteintes par I'excitation infrarouge ou thermale, les quatre ellipso'ides se combinent en deux halthres de rkvolution. La resonance isotrope des klelectrons de masse effective m* = 0.75 m, sugghre l'existence d'une bande interdite qui est indirecte 8. temperature basse. Valence BandThe problem of the valence band structure of tellurium has recently been clarified. A Shubnikov -de Haas paper [l], the preliminary report of the present work [2], and recent cyclotron resonance work by Couder [3] have independently culminated in a detailed model which is able to suggest a continuity among various experimental results. We shall first summarize the Shubnikov -de Haas work and then present our own observations. Guthmann and Thuillier [l] studied the anisotropy of Shubnikov -de Haas oscillations as a function of impurity concentration. They concluded that for carrier concentrations less than 1.5 x lO17/cm3 the tellurium Fermi surface is described by a set of 4 ellipsoids of revolution about the c-axis located near the corners of the Brillouin zone (see Fig. 1 a). (This result is consistent with the first report of cyclotron resonance in tellurium by Mendum and Dexter [4].) At higher hole concent'rations, pairs of ellipsoids degenerate into dumbbell-shaped surfaces centered a t the Zone corners (Pig. 1 b). Earlier Shubnikov -de Haas results [5 to 71, as well as numerous other experiments, had suggested one or the other of these two qualitatively distinct regimes. Guthmann and Thuillier were able to resolve the apparent contradiction between these divergent conclusions with the aid of several theoretical papers [8 to 101 which placed the valence band maxima on the Brillouin zone edges near the corners H (called M and P in the notation of PI). l)

No abstract