A. C. and D. C. Field Effects on Cleaned Germanium Surfaces

Measurements of the a.c. and d.c. field effects were made on the conductance of the germanium surfaces cleaned by Joule heating up to about 800°C in ultra-high vacuum. In the measurements of the a.c. field effect on the cleaned surface, the minimum of conductance showing the surface was slightly n -type was observed and the density of fast states was estimated at 1.7×10 13 /cm 2 ·volt. When the surface was exposed to oxygen, the fast state density decreased down to 2.4×10 12 /cm 2 ·volt and the surface potential decreased by 0.03 volts. These results suggest that the fast states are dangling bonds at the surface. In the measurements of the d.c. field effect on the cleaned surface, the slow decay of the changes in conductance was not recognized. The slow decay appeared when the surface was exposed to air. These results show that the slow states are attributed to adsorbed gases on the outer surface of the oxide layer of germanium.