Lattice Disorder Effects on The Vacancy-Oxygen Centre in Ion-Irradiated Silicon

Abstract

ABSTRACTThe Vacancy-Oxygen (VO) centre is one of the most prominent defects appearing in silicon after irradiation with energetic particles and gamma rays. It is formed when migrating vacancies are trapped by interstitial oxygen atoms. It gives rise to a deep level in the upper part of the silicon bandgap at 0.164 eV below the conduction band edge that can be conveniently studied by deep level transient spectroscopy (DLTS). It is furthermore a very important defect from a technological point of view since it normally controls the charge carrier lifetimes in silicon power devices at high injection levels.Various doped n-type float zone Si samples have been irradiated with MeV ions at low doses. DLTS measurements of the charge carrier capture kinetics reveal lower capture rates if heavier ions, i.e. larger collision cascades, have been used to generate the defects. This effect can be interpreted as a local lowering of the Fermi level following lattice disorder in regions with a high elastic energy deposition. It will be shown that the VO is also very sensitive to lattice disorder in a similar way as previously reported for the divacancy centre.In the DLTS spectra another defect, originating from an interstitial-carbon—substitutional-carbon pair (Cj-Cs), overlaps with the VO-peak. The Ci-Cs pair has been observed to posses bistable properties and in this paper we will further elucidate the various contributions from the two defects to the Ec-0.164 eV peak. In particular, the temperature dependence of the electron capture cross section of the Cj-Cs level will be discussed.