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 °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.

Self-Interstitial in Germanium

“…Investigations of the variation of the densities of P1 and free holes with temperature [7,8] place the (=2) level of the two-state donor defect about 0.1 or 0.2 eV below E c in agreement with the calculations for the interstitial at the cage site (Table II). This assignment is also consistent with the measured capture cross sections for electrons of 10 ÿ15 cm 2 , and <10 ÿ27 cm 2 for holes of the 0 state (I ) [6].…”

“…The stable state in p-Ge is but a burst of free electrons from ionizing radiation puts the defect into the 0 state. The latter state is correlated with the S 1=2 P1 electron paramagnetic resonance (EPR) center and must therefore have an odd number of electrons [7]. Thus the true charge state of the 0 state cannot be neutral as has been assumed [8].…”

“…Injecting electrons into the conduction band leads to the conversion of I 2 T into I and I 0 . It is I and I 2 which are to be identified with the 0 and states of the two-state donor defect which is observed in this temperature region: in the 0 state, I is the P1 S 1=2 EPR center [7], which must contain an odd number of electrons and excludes an identification with neutral I. The two-state donor defect cannot be a vacancy as the latter acts only as an acceptor.…”

“…Between 100 and 200 K, the free hole concentration decreases and a strange ''two-state'' defect is observed [6 -8]. This defect, which seems to be an intrinsic donor [7,8], is a long-lived electron trap that can be cycled between two charge states, denoted '''' and ''0'', with a transition level around E c ÿ 0:2 eV [7,8]. The stable state in p-Ge is but a burst of free electrons from ionizing radiation puts the defect into the 0 state.…”

Dangling bonds and vacancies in germanium

“…[21][22][23] In the study by Fazzio et al, 21 modifications were made to the germanium pseudopotential, whileŚpiewak et al 22 employed LDA+U and Tahini et al 23 used GGA+U . Vacancies in germanium have been studied by ESR, 25 Hall measurements, [26][27][28] positron annihilation spectroscopy,…”