32 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1953 



0.08 



-0.06 



0.36 0.40 0.44 0.48 0.52 0.56 0.60 0.64 0.68 0.72 0.76 0.80 

 CONTACT POTENTIAL IN VOLTS 



Fig. 18 — Potential across space charge layer, Vb , versus contact potential. 



also 8V% for certain special cases for samples A and D as calculated 

 from theory. From equations (8) and (10) 



(V. 



BO 



e 



2/3 



ln(p/n). 



(38) 



It is a constant for any given sample as is dVi (see equation 15). From 

 equations (21) and (38) it follows that when 8Vb = then (Vb - Vq) = 

 for all samples. To say this another way, if the traps are symmetrically 

 distributed about Ei and Vb is zero, then illuminating the germanium 

 would produce no potential difference across the surface. One would not 

 suspect offhand that (Vb - Vq) for 8Vl = was also approximately 

 independent of the material in the sample but it is. For the case where 

 5p and the minority carrier are both small compared to the majority 



