LENGTH CHANGES IN ELECTRON-IRRADIATED n- AND p-TYPE GERMANIUM

Simultaneous length-change and conductivity measurements of $n$-type and $p$-type germanium single crystals have been made as a function of irradiation by 4.5-MeV electrons at liquid-helium and liquid-nitrogen temperatures and subsequent isochronal annealing. Changes in length of the samples produced changes in the spacing of a system of parallel-plate capacitors, and these capacitors were compared with a standard capacitor by means of an ac ratio bridge. The sensitivity and long-term stability of the system were such that changes in length on the order of 0.1 \AA{} were detectable. Degenerate $n$-type material was found to contract during irradiation at both liquid-helium and liquid-nitrogen temperatures. Length and conductivity annealing stages were observed at both 35 and 65\ifmmode^\circ\else\textdegree\fi{}K during isochronal annealing. Length changes in degenerate $p$-type material were at least an order of magnitude smaller than in $n$-type. The $p$-type sample expanded slightly during irradiation at liquid-nitrogen temperature. These length-change results are interpreted in terms of an electronic-volume effect in addition to the usual atomic-volume effect. The measurements helped to confirm the model deduced from the results of electrical measurements which predicts that the effect of electron irradiation on germanium is strongly dependent upon the doping of the material.