842 THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1951 



The transit time r from the first plane to any coordinate x is 



and 



The total transit time T across the diode space also plays an important 

 role; it is usually expressed in terms of a so-called space charge factor f, 

 whose value is given by^ 



(■ - 



tk 



Here / is the actual d-c. current; and Im is the maximum current that could 

 be projected across the diode when its planes are at the voltages Va and Vb, 

 that is, Im is the space charge Hmited current 



^3 



r = ^ , /2 (VVa + VVl>y 



" 9 y 77" p 



Then the total transit time T is given by 



21 



T = 



{i-Q[u.+ u.) 



(36) 



(37) 



It also follows that I can be expressed in the form 



/ = % {Ua + U,) (38) 



Certain equations for the d-c. electric intensity are also required. They are 



rjl 2€ 



£» = ^ (f/a - i/6) - J 



They complete the list of d-c. relations required in the following small 

 signal theory. 



