18 - 3
become very noticeable. At NA = 10 cm , the highest value of rS is 1.29 for T = 100 K, where the dopant impurities are only about 30 percent ionized [17]. At higher temperatures where the percentage of ionized impurity atoms is 'over 80 percent, the effects of hole-hole scattering bring rS from its traditionally expected value of 1.93 to
1.05 for T = 400 K.
5.5 Hall Mobility and Hall Factor in the Combined Valence Band
Expressions for Hall coefficient, applicable in the case where holes in more than one band take place in conduction, are given by Putley [66]. For the case of p-type silicon, assuming no compensation and operation in the low field region, the Hall coefficient is given by [66]
3 2
RHilCi
RH = i=l (5.10)
.= i
By substituting equations (2.9) and (5.6) through (5.10) into equation (5.-4), the Hall mobility in the combined valence band of silicon can be expressed by
3 m*i3/2
i i
PH e 3 3/2
i=l mCi