No 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 °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 Q cm. No resolved hyperfine spectra were observed. The predominant set of lines represents a spin-J center, designated Ge-Pl, whose g tensor has (100)(011) symmetry, with g[0ll] =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-Pl center; however, the high degree of symmetry of the g tensor suggests that the structure of the defect is simple.

The ionization afterglow techniques involve the production of electron-ion pairs in a gas by a short pulse of high energy nuclear radiation, 20 to 30 MeV electrons in this case. The electron density and electron-atom collision frequency are measured by passing through the dilute plasma formed a microwave signal, whose amplitude and phase shift are measured with a microwave detector in a bridge configuration. An X-band microwave cavity and a 300 Mc cavity have also been utilized to perform measurements with higher sensitivity at lower pressures. The results from these experiments include determinations of electron attachment and electron-ion recombination co-efficients as well as momentum and energy transfer cross sections. In common with other afterglow techniques, the measurements usually refer to a thermally averaged electron energy spectrum. Some specific examples from studies of momentum and energy transfer, as well as electron-ion recombination in nitrogen, are presented.