Deep-level transient spectroscopy study of the E center in n-Si and partially relaxed n-Si0.9Ge0.1 alloy layers

We have employed deep-level transient spectroscopy to investigate the electronic properties of defects introduced during high energy He-ion irradiation of epitaxially grown phosphorous-doped n-Si and partially relaxed n-Si0.9Ge0.1. It is found that He-ion irradiation introduces two major defects in Si and Si0.9Ge0.1. These have been attributed to a doubly negative charge state of the divacancy (V-2(=/-)) and V-P pair (E center). The germanium dependence of the activation enthalpy (E-H) for both (V-2(=/-)) and V-P pair is found to be relatively minute with a small decrease and increase in the corresponding E-H with respect to that of Si, respectively. Comparison was made with earlier reported results in phosphorous-doped fully strained n-Si1-xGex and antimony-doped totally relaxed n-Si1-xGex layers to directly assess the influence of strain relaxation on radiation-related deep levels in Si1-xGex. It is shown that the energy level of the V-P pair in fully strained and partially relaxed Si1-xGex lies closely to that reported for V-Sb in fully relaxed Si1-xGex. This result indicates that the V-P level is independent of strain, suggesting that such defect is pinned to the conduction band. Moreover, our calculation using full-potential linearized augmented plane wave method shows nonpreferential site occupancy of the phosphorous relative to Ge atoms. This implies a chemical disorder in the vicinity of the V-P center which leads to a fluctuation of the ionization energy level of the E center. This fluctuation is associated with a distribution of the electron emission rate between the V-P level and the conduction band edge.