Effect of Vacuum Heating and Ion Bombardment of Germanium on Point Contact Rectification

Abstract

An apparatus is described which allows the cleaning of the contact surfaces by vacuum heating and argon ion bombardment. The diode characteristics of a tungsten and a columbium point against the same germanium crystal are measured while a high vacuum is maintained in the experimental tube. If the germanium is heated to above 800°C and cooled suddenly, the room-temperature rectification is lost. The rectification is restored by vacuum annealing at 500°C for 10 hr. The best rectification characteristic is obtained after the germanium has been subjected to a long anneal, argon ion bombardment, and a short anneal. This sequence of treatments approximates that yielding the low-energy electron diffraction pattern to be expected from a pure germanium surface. The diode activation potential, determined from the temperature dependence of the low-level resistance, is shown to change experimentally with the treatment of the semiconductor and with the contact force. With the techniques used, an experimental dependence of the diode activation potential on the metallic work function is not evident. A theoretical expression for the activation potential is given in the Appendix.