Contact Potential Measurements on Cleaned Germanium Surfaces

The contact potential of the (110) face of the n and p regions of an n-p germanium crystal was measured in a vacuum of less than 10-9 mm Hg using a Kelvin bridge technique. The n and p regions were so doped that their resistivities were 0.058 and 0.33 ohm-cm, respectively. If there had been no surface states the difference in work function would have been 0.34 ev. The argon-cleaned surface exhibited a difference of 0.002(±0.004) ev. An exposure of as little as 0.4×10-7 mm-min of oxygen increased the difference to 0.013 ev. A difference as large as 0.018 ev was observed after a 28×10-7 mm-min exposure. After 56×10-7 mm-min the difference was reduced to 0.000(±0.005) ev. These results are discussed in terms of several surface state distributions. © 1959 The American Institute of Physics.