1310 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1953 



s = (1 + iojt) 



T = temperature in degrees Kelvin (absolute temperature) 

 Ve , Veo , Vei , Vc , Vco , Vd = total, average, and ac emitter and col- 

 lector potentials. 

 Vc = average collector potential 



w, Wo , Wi = total, average, and ac variation of base-layer thickness 

 X = distance from emitter barrier 

 Xm = thickness of collector barrier layer 

 y = distance from collector side of collector barrier layer 

 Vee , Vce , Vec , Vcc = short-clrcult ac admittances 

 a = current amplication factor 



jS = base-layer transport factor • 



pc = resistivity of collector region 

 ppc = resistivity for holes in collector region 



<Tpc , o'nc = conductivities for holes and electrons in collector region 

 r = minority carrier lifetime 

 fin = electron mobility 

 Up — hole mobility 

 0) = angular frequency in radians 



Appendix B 



base layer spreading resistance 



Significance 



The bulk resistance of the base layer or base layer spreading resistance 

 (vb) is important because base current passing through n' produces a 

 base contact to emitter junction negative feedback voltage ibTb. Re- 

 duction of Tb is an important objective in improvement of junction 

 units. 



Types 



Since feedback voltage to the emitter junction is produced by two 

 separately measurable base current components having very different 

 flow paths, two separately measurable base layer spreading resistances 

 (vbi and rb2) may be defined. 



The current (l-(x)ie originates in the base layer between the emitter 

 and collector junctions and flows radially through the base layer to the 

 base contact producing a feedback voltage at the emitter; n'l is defined 

 as the ratio of this feedback voltage to the current. 



The collector capacitance current joiCcVc enters the base layer uni- 



