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Drift velocity of hot electrons in n-type germanium Burgess, Ronald Reginald

Abstract

The drift velocity of electrons in n-type germanium has been measured as a function of applied electric field at lattice temperatures of 77°K and 295°K. Three directions of applied field were used, viz. (1, 0, 0), (1, 1, 0) and (1, 1, 1) crystal directions. The range of field strength was from 100 v/cm to 75 kv/cm. A longitudinal anisotropy was observed at 77°K but not at 295°K. At 77°K the drift velocity for a given field strength was greatest in the (1, 0, 0) direction and least in the (1, 1, 1) direction. All specimens showed saturation of the drift velocity at high fields. In no case did the drift velocity show a further increase with increasing electric field once it had saturated. At 77°K, all (1, 0, 0) specimens exhibited a breakdown effect, the cause of which is not known. Its characteristics could not be correlated with any properties of the specimens. The results are analysed on the basis of an extension of Stratton's theory to the case of a many-valley semiconductor. It is assumed that intervalley scattering does not affect energy relaxation, but does contribute a shift in the relative populations of the conduction band valleys. This theory is successful at low fields. It predicts an anisotropy at 77°K while predicting none at 295°K. However, it predicts too much anisotropy at low fields at 77°K. It also predicts an anisotropy at high fields at 295°K. Suggestions are made as to possible reasons for these discrepancies.

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