Electron Paramagnetic Resonance in Electron-Irradiated Germanium

Abstract

Spin-resonance studies have been made in oxygen-free $p$-type germanium after bombardment by 4.5-MeV electrons. Samples were bombarded and stored at 77\ifmmode^\circ\else\textdegree\fi{}K, and measurements were made at liquid-helium temperatures with a superheterodyne spectrometer operating at 9500 MHz. Essentially the same resonance spectra appeared in both undoped and gallium-doped germanium samples that initially had room-temperature resistivities in excess of 40 \ensuremath{\Omega} cm. No resolved hyperfine spectra were observed. The predominant set of lines represents a spin-\textonehalf{} center, designated Ge-$P1$, whose $g$ tensor has $〈100〉〈011〉$ symmetry, with $g[01\overline{1}]=2.025$, $g[011]=1.629$, and $g[100]=1.732$. The line width is 70 G. The production rate of the center is approximately 1.6 ${\mathrm{cm}}^{\ensuremath{-}1}$. The defect exhibits some of the characteristics of a long-lived electron trap. The traps begin to empty, as evidenced by a gradual decrease in the resonance signal, when the sample is warmed above 77\ifmmode^\circ\else\textdegree\fi{}K. At 135\ifmmode^\circ\else\textdegree\fi{}K the traps empty in seconds. The resonance signal returns when the traps are repopulated by a short burts of ionizing irradiation at 77\ifmmode^\circ\else\textdegree\fi{}K. When the sample is warmed above 220\ifmmode^\circ\else\textdegree\fi{}K, the center loses its trapping property and is assumed to have disappeared or changed its form. An analysis of the $g$ shift and the trapping behavior is not sufficient to give a definite microscopic model of the Ge-$P1$ center; however, the high degree of symmetry of the $g$ tensor suggests that the structure of the defect is simple.