820 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1954 



It is seen that values of — Q as small as about 10 can be obtained for 

 13 ^ 3. 



In the next section we shall consider modifications which may result 

 from variations in n* and for changes in geometry. 



We must return to the question of how the charge +5Qi passes the 

 potential maximum. In order that the theory given above apply, it is 

 necessary that the time required for 8Qi to enter the drift region be short 

 compared to the transit time. At the potential maximum the charge 

 density may be estimated by the methods previously dealt "with in the 

 theory of space charge limited emission. Initially -\-8Qi appears to the 

 left of the maximum and the field at the maximum is 8Ei . This field will 



10-2 



100 200 300 400 500 600 700 800 

 6 IN DEGREES 



Fig. 4.5 — Impedance of a p-n-p structure, (c) Real part of impedance. 



