The Mobility and Life of Injected Holes and Electrons in Germanium

AS a result of new experimental techniques 1 developed in connection with the transistor2 program, the speed with which holes and electrons drift in electric fields in germanium can now be measured with an accuracy sufficient to determine their mobilities to within a few percent. The basic phenomena which permit these new experiments to be performed are those of carrier injection 3 and collector action ;2 with the aid of the former, holes or electrons can be injected at a given place and time, and with the aid of the latter their arrival time at another point can be determined. It should be emphasized that transit time measure­ ments determine drift mobility in a very direct way. Hall effect measurements, which have previously been used to determine mobilities in semiconductors, are quite indirect. The relationship between Hall mobility, defined by the angle between current and electric vectors in unit magnetic field, and true mobility involves the detailed nature of the scattering processes and energy band shapes and only under special condi­ tions does the ratio have the conventional value of 31r/8. It now appears probable that a real deviation from the simple ratio 31r/8 occurs for electrons in ger­ manium and that this is associated with energy band shapes. 4