Electrically active defects induced by irradiations with electrons, neutrons and ions in Ge-rich SiGe alloys

Abstract

Results of DLTS and high-resolution Laplace DLTS measurements of electrically active defects induced in phosphorus-doped dilute Ge-rich SiGe (0⩽[Si]⩽6 at%) samples by irradiations with 60Co gamma-rays, fast neutrons and 1–3 MeV Si ions and by ensuing annealing are presented in the work. It has been found that the DLTS spectra of these germanium rich SiGe samples irradiated with gamma-rays are qualitatively similar to the spectra of similarly irradiated Ge samples, which do not contain Si. The DLTS spectra of the gamma-irradiated samples are dominated by the E-center (vacancy–phosphorus pair). This indicates that silicon impurity atoms are not effective traps for vacancies in Ge at room temperature. Further, we have found no evidence for possible interactions of Ge self-interstitial atoms with Si atoms upon room temperature electron irradiation of SiGe samples. The presence of Si impurity atoms does not influence significantly the annealing behavior of the E center in Ge-rich SiGe. Thirty-minute heat treatments of the gamma-irradiated samples at 300 °C have resulted in complete removal of radiation-induced damage. DLTS spectra of the SiGe samples after low dose neutron irradiation resemble those observed after gamma irradiations, however, in the neutron-irradiated samples a few more minor DLTS peaks have been observed. The neutron-radiation-induced defects can be removed by anneals at 300 °C. The situation in ion-implanted material is more complex. Point defects, which dominate the DLTS spectra of electron-irradiated SiGe samples, are not the main electrically active traps in the ion-implanted samples. The Laplace DLTS spectra of the implanted samples show evidence of broader features characteristic of defect clusters. The implantation-induced damage is much harder to remove by heat treatments compared to the radiation-induced one. Significant concentration of electrically active traps remain in SiGe samples implanted with high doses of ions even after anneals at 500 °C.