POINT-CONTACT TRANSISTOR SURFACE EFFECTS 



803 



to semiconductor contact, more efficient forming probably results on 

 surfaces which display very low initial saturation currents. On surfaces 

 which produce a poor initial rectifying diode, the local energy of the 

 forming pulse may be dissipated too far out into the bulk of the semi- 

 conductor. This situation would result in inefficient forming. 



Since the low-voltage diode characteristics and the forming are proba- 

 l)ly related, one should be able to predict the "foi-mability" of any par- 

 ticular surface. Fig. 16 shows that this can be done qualitatively. In the 

 (!,raph each point represents the average of at least five units formed 

 on electro-etched surfaces to the forming objective, Fc(3, —5.5) ^ 2.0 

 ^'olts. Fig. 16(a) represents the reverse emitter current before forming 

 plotted on a log scale versus the percentage of units taking more than five 

 pulses to form. The reverse emitter current rather than the reverse col- 

 lector current is a desirable preforming parameter to use since this pre- 



100 



80 



Z 60 



UJ 



o 



cr 

 LU 40 



D. 

 20 



0.02 0.04 0.06 0.1 0.2 0.3 0.4 0.6 0.8 1.0 



CURRENT, Igl'^OjO) IN MILLIAMPERES (BEFORE FORMING) 



Fig. IG — Relation of forming to pre-forming characteristics: electro-etched 

 surfaces. 



