Electrical Measurements on Clean and Oxidized Germanium Surfaces

Abstract

Simultaneous measurements of surface conductivity $\Delta \sigma$ 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×${10}^{-6\mathrm{}}$ Torr min, $s$ started to increase and reached a value greater than that for the clean surface. The change of both $s$ and $\Delta \sigma$ with oxygen adsorption depended strongly on the annealing temperature. The surface potential $u_s$ 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×${10}^{-6\mathrm{}}$ 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 ${\mathrm{cm}}^2$ ${\mathrm{V}}^{-1\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ and $p$ type, that of the clean (100) surface 165 ${\mathrm{cm}}^2$ ${\mathrm{V}}^{-1\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ ($p$ type).