COMBINED MEASUREMENTS ON ETCHED GERMANIUM SURFACES 



1025 



reduce the high field that would otherwise be present near the edges of 

 the ceramic. The gold electrode was deposited by evaporation through 

 a mask. Connections from the gold and from the ends of the sample were 

 made to binding posts passing through the ceramic block. 



The ceramic block was set into a metal box, divided into two com- 

 partments. In the upper compartment, which contained the sample, 

 there were inlet and outlet tu}:)es, to allow the gas to be changed. The 

 lower compartment contained electrical components, which were 

 thereby protected to a large extent from the changes in gas in the upper 

 compartment. Facilities were available for the type of cycle of gas en- 

 vironment described by Brattain and Bardeen,^ which cycle was found 

 by them to produce reversible cyclic changes in surface potential. In 

 the top of the box was a window, through which light could be shone 

 onto the germanium either from a chopped or a flash source. 



The electrical circuit is shown in Fig. 2. The condenser Ci is that 

 formed between the germanium and the gold, and has a capacity of 

 about 2 ijlijlF. Impedances Zi and Zo form a Wagner ground, which has 

 to be balanced first. Then, by adjusting resistance Ri and condenser 

 C2 , one may obtain a balance in the case that there is no dc flowing 

 through the sample. A current (determined by the battery B and the 



HORIZONTAL 



VERTICAL 



ELECTROMETER - 



TUBE 

 PRE-AMPLIFIER 



:!^ B 



Fig. 2 — Electrical circuit. 



