THE BELL SYSTEM 



TECHNICAL JOURNAL 



VOLUME XXXII JANUARY number 1 



Copyright, 195S, American Telephone and Telegraph Company 



Surface Properties of Germanium 



By WALTER H. BRATTAIN* and JOHN BARDEENt 



(Manuscript received September 3, 1952) 



The contact potential (c.p.) and the change of contact potential with il- 

 lumination {Ac.p.)l of several germanium surfaces have been measured. 

 The reference electrode used was platinum. It was found that the c.p. could 

 be cycled between two extremes about 0.5 volts apart by changing the gaseous 

 ambient. Ozone or peroxide vapors gave the c.p. extreme corresponding to 

 the largest dipole at the Ge surface. Vapors with OH radicals produced the 

 other extreme. There is a one to one correlation between c.p. and (Acp.)/, . 

 For 12-ohm cm n-type Ge (Ac.p.)L was large and positive when the surface 

 dipole was largest, decreased to zero and became slightly negative as the 

 surface dipole decreased to its smallest value. The variation for 12-ohm 

 cm p-type Ge was just opposite as regards both sign and dependence on 

 surface dipole. The surface recombination velocity was found to be inde- 

 pendent of c.p. For a chemically prepared surface it was 50-70 cm/sec 

 and 180-200 cm/ sec for n and p-type surfaces respectively. A theory is 

 given that explains the results in terms of surface traps, Na per cm donor- 

 type traps near the conduction band and Nb per cm acceptor-type traps 

 near the filled band. A quantitative fit with experiment is obtained with 

 only one free parameter. The results are direct evidence for the existence 

 of a space charge layer at the free surface of a semiconductor. 



INTRODUCTION 



Every one is familiar with the fact that it is necessary to expend 

 energy to remove an electron from a conducting solid. This energy is 



* Bell Telephone Laboratories. 



t University of Illinois. The contributions of the second author to this work 

 started while he was a Member of the Technical Staff of Bell Telephone Labora- 

 tories and continued at the University of Illinois. 



