Electron Paramagnetic Resonance in Electron-Irradiated Germanium

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^∘{}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 {Ω} cm. No resolved hyperfine spectra were observed. The predominant set of lines represents a spin-{} center, designated Ge-$P1$, whose g tensor has $〈100〉〈011〉$ symmetry, with g[011̄]=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 cm^-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^∘{}K. At 135^∘{}K the traps empty in seconds. The resonance signal returns when the traps are repopulated by a short burts of ionizing irradiation at 77^∘{}K. When the sample is warmed above 220^∘{}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.