CONDUCTIVITY-MODULATED SILICON RECTIFIER 



995 



CAPACITANCE IN MICROMICROFARADS PER SQUARE CENTIMETER 



Fig. 11 — Capacity/cm^ for high voltage rectifiers processed from various types 

 of high resistivity material. 



ties measured by the four point probe before diffusion are indicative of 

 the impurity level after processing. The water vapor floating zone re- 

 fined material has an impurity level of lO'" acceptors/cm^ the other 

 material is in the range of lO'^ to 10^\ The breakdo^vn ^'oltage line was 

 calculated from the data in Fig. 5. 



0.2 Diffusion 



In this section some of the practical difficulties observed in utihzing 

 the diffusion techniciue will be considered. In the fabrication of transis- 

 tors close geometry control is necessary in order to obtain the desired 

 device characteristic. It has been shown^ that in conductivity modulated 

 rectifiers the only geometry rec[uirement is that the ^^^dth of the center 



