CHAPTER V

                  THE HALL FACTOR IN p-TYPE SILICON


 5.1 Introduction

      The most direct determination of the mobility is by the HaynesSchokley drift method, wherein the drift of charge carriers in a known electric field is measured. However, the assumption, made when these experiments were ini tiated, that the drift mobility of holes as minority

 carriers in an n-type sample is the same as when they constitute the majority carriers, is invalid in view of carrier-carrier scattering [59]. Also the experiment can succeed only if the lifetime of the minority carriers is larger than the transit time. For this reason, usually Hall mobilities are measured instead. The Hall mobility is the product of the measured conductivity and the measured Hall coefficient. In general the Hall mobility differ-s from the conductivity mobility by a factor called the Hall factor. Determination of the Hall factor may' be avoided by making use of the high field limit. For sufficiently high magnetic fields several simplifications occur in the magnetic field dependence of the Hall coefficient.   In the high-field limit (when the.

*product of mobility and magnetic induction becomes g reater than 10O8 cm-2 gauss/volt-sec [60]) the Hall coefficient is simply related to the
carrier concentration by [61]


        RH1(51
           H pe