Combined Measurements of Field Effect, 



Surface Photo-Voltage and 



Photoconductivity 



By W. H. BRATTAIN and C. G. B. GARRETT 



(Manuscript received May 10, 1956) 



Combined measurements have been made of surface recombination veloc- 

 ity, surface photo-voltage, and the modulation of surface conductance and 

 surface recombination velocity by an external field, on etched germanium 

 surfaces. Two samples, cut from an n-type and a p-type crystal of known 

 body properties, were used, the samples being exposed to the Brattain- 

 Bardeen cycle of gaseous ambients. The results are interpreted in terms of 

 the properties of the surface space-charge region and of the fast surface 

 states. It is found that the surface barrier height, measured with respect to 

 the Fermi level, varies from —0.13 to -\-0.13 volts, and that the surface 

 recombination velocity varies over about a factor of ten in this range. From 

 the measurements, values are found for the dependence of charge trapped 

 in fast surface states on barrier height and on the steady-state carrier con- 

 centration within the semiconductor. 



I. INTRODUCTION 



This and the succeeding paper are concerned with studies of the 

 properties of fast surface states on etched germanium surfaces. The ex- 

 periments involve simultaneous measurement of a number of different 

 physical surface properties. The theory, which will be presented in the 

 second paper, interprets the results in terms of a distribution of fast 

 surface states in the energy gap. The distribution function, and the 

 cross-sections for transitions from the states into the conduction and 

 valence bands, may then be deduced from the experimental results. 



Early experiments^ on contact potential of germanium, and on the 

 change of contact potential with light, indicated that there are two 

 kinds of surface charge associated with a germanium surface, over and 

 above the holes and electrons that are distributed through the surface 

 space-charge region. One kind of surface charge, usually called "charge 



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