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-½ center, designated Ge-$P1\mathrm{}$, whose $g$ tensor has $〈100〉〈011〉$ symmetry, with $g\left[01\mathrm{}\overline{1}\right]=2.025\mathrm{}$, $g\left[011\right]=1.629\mathrm{}$, and $g\left[100\right]=1.732\mathrm{}$. The line width is 70 G. The production rate of the center is approximately 1.6 ${\mathrm{cm}}^{-1\mathrm{}}$. 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-$P1\mathrm{}$ center; however, the high degree of symmetry of the $g$ tensor suggests that the structure of the defect is simple.