Field Effect in Germanium at High Frequencies

Changes in conductivity near the surface of germanium in response to an ac electric field have been investigated at frequencies as high as 50 Mc/sec for both $n$- and $p$-type material, and in wet air, dry oxygen, and ozone ambients. In certain ambients the sign of the field effect changes at a frequency closely related to the reciprocal of the minority carrier lifetime. At higher frequencies the field effect mobility is sometimes substantially larger than bulk mobility of the majority carrier. A model is suggested which is in harmony with most the experimental observations.