Electrical Measurements on Clean and Oxidized Germanium Surfaces

Simultaneous measurements of surface conductivity Δσ and surface recombination velocity s were performed on 15 {Ω}-cm n-type germanium samples, cut perpendicular to the (111) or (100) axis. Clean surfaces were obtained by Farnsworth's technique of ion bombardment and anneal; the electrical measurements were performed with a Many bridge. The s of clean (111) surfaces varied between 730 cm/sec and 480 cm/sec and first decreased with oxygen adsorption. After an adsorption of about 300×{}10^-6 Torr min, s started to increase and reached a value greater than that for the clean surface. The change of both s and Δσ with oxygen adsorption depended strongly on the annealing temperature. The surface potential uₛ of the clean surface was -9.9; i.e., strongly p-type but not degenerate. The s of the clean (100) surfaces varied between 320 cm/sec and 1040 cm/sec and changed very little with oxygen adsorption up to 50×{}10^-6 Torr min, it then either decreased or continued to remain constant. The surface potential of the clean (100) surface was -14; i.e., degenerate p type. The field effect mobility of the clean (111) surface was 80 cm² V^-1 sec^-1 and p type, that of the clean (100) surface 165 cm² V^-1 sec^-1 (p type).