Impurity conduction of cleaned germanium surfaces at low temperatures

Abstract

The conductivity and Hall effect of cleaned germanium surfaces have been measured in the temperature range between 1.7°K and 300°K. The surface was cleaned by Joule heating at ~ 800–850°C in ultra-high vacuum for ~ 20—30 hr and was then annealed at 650°C for several hours. Results obtained with ~20–40 Ω-cm p-type samples show that the Hall coefficient has a steep maximum at ~ 10–20°K and the resistivity becomes almost flat below this temperature range. This character is similar to that of bulk impurity conduction found by H ung et al., but disappears on exposure to air which causes marked increases in both the Hall coefficient and resistivity at low temperatures. This impurity conduction is attributed to the surface imperfections introduced by the cleaning treatment of the surface. The mobility and concentration of carriers in this surface conduction are estimated.