812 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1954 



>S2 has much higher impedance than Si . Si has higher impedance than 

 that for hole injection into N. The impedance for hole injection into A^ 

 corresponds to the hole conductivity in the n-layer over a distance com- 

 parable with the thickness of .V. However, the impedance of A^ itself is 

 that due to the much larger number of electrons in it and is thus much 

 less than the impedance of *Si . Thus it follows that the impedances 

 across Si and across A^ are much less than across S2 . This conclusion is 

 not affected by the modification of impedance of S2 due to hole flow 

 across it. 



3.3. Modifications 



The treatment presented abo\'e has been based upon the conditions 

 (a) to (e). Some of these are advantageous from the point of ^'iew of 

 operation but others have been introduced to simplify the treatment. 

 Among the latter is the condition that the current across Si is carried 

 chiefly b}^ holes. If the current were chiefly capacitative at this junction, 

 then the voltage would lag 90° behind the current. This adds a desirable 

 phase lag in the hole injection across >Si and thus requires less phase shift 

 in the n-layer. By suitably'' adjusting the ratio of capacitative and in- 

 ductive admittances, a net improvement in Q may be obtained. 



4. THE TRANSIENT RESPONSE IN A UNIPOLAR STRUCTURE 



In the previous section the electric field produced by the injected holes 

 had a neghgible influence on the motion of the injected holes. In effect 



(a) 



(b) 



Hg. 4.1 — Space charge limited hole flow. 



