Measurement of high-field carrier drift velocities in silicon by a time-of-flight technique

In this paper we describe a time-of-flight technique which has been used to measure the drift velocities of carriers in silicon at high electric fields. Carrier velocities are determined absolutely by measuring the transit time of carriers through a region of approximately uniform electric field and known width in a p⁺-ν -n⁺diode. The transit time is obtained directly as the duration of the sample current pulse following bombardment of one face of the p⁺-ν-n⁺diode with a very short pulse of 10-keV electrons. The ratio of the known sample width to the measured transit time gives the carrier velocity for a particular value of electric field. The carrier-velocity data thus obtained are absolute, with an accuracy of approximately ± 5 percent. Drift-velocity data for carriers in silicon are presented for electric fields between 4 and 40 kV/cm and the present data are compared with those obtained from measurements of current density in bulk samples as a function of electric field.