~rift mobili ty techni:ucs hnvc been \ \sec. to maD ,"urc the trDDP. 'oct of generated electrons in single crystals of orthorhombjc sulphur grown from solution. The drift mobility was found to be the SaT:1e for more than 20 specimens grown from starting materials of different degrees of purity, despite large differences in hole mobility measured on the same specimens. At 21 °c , JA .. = 6.2 x 10- 4 cm 2- V- 1 sec- 1 and was found to increase with temperature as exp( -E.ykl')) where Eo. = 0.167 eVe ~,. exhi bi terJ no measur~able Dnisotropyo The transformation to the monoclinic modification is accompanied by a fall in mobility by a factor of about ten and an increased density of deep traps. The electron mobility results are shovm to be consj stent wjth IOn intermolecular hopping mechanism jn vrhj ch the clcctT'll:n j l;(~Ci.'i'r:ts with one or more molecular vibrational modes. It is believed that this is the first time a strong case for a true hopping current has been presented. The polaron binding energy is shown to be 0.48 eV and the dimensionless electron-lattice interaction parameter, Y~18. The isolated 88 molecule and its ions are eXaIDjnea theoretically in terms of molecular orbital theory and the study is extended in an estimate of the electron and hole bandwidths in the solj(J by Em approximate method. A number of intraTllolecular ana intermolecul[cr orbital overlaps are calculated and the results are used in a discussion of the electron mobilityo The electron free lifetime at the surface and in the bulk was studied by a novel method involving interrupted electron transjts. The trapping spectrum was investigated by thermally stimulateo conductivity and by an electron beam probing technique which was used to study the polarization decay. The results lend support to the hopping interpretation cf electron transport. A subsisiary study of space-charge perturbed electron currents provides experimental confirmation of a recent theoretical treatment by Papadakis.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:559718 |
| Date | January 1965 |
| Creators | Gibbons, David John |
| Publisher | University of Leicester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/2381/27693 |
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