Role of the impurities in production rates of radiation-induced defects in silicon materials and solar cells

摘要

The present extensive systematic study of defect introduction rates as a function of boron, gallium, oxygen, and carbon concentrations by means of deep level transient spectroscopy has drawn a quite complete picture towards the identification of the dominant radiation-induced defects in Si. The radiation-induced defect E_(V)+0.36 eV has been identified as C_(i)-O_(i) complexes. The absence of an E_(C)-0.18 eV complex center in gallium-doped samples and the linear dependence of its introduction rates on both the boron and oxygen content fixed its identification as the B_(i)-O_(i) complex in boron-doped Si. One of the technologically important results of present study is that the gallium appears to strongly suppress the radiation induced defects, especially hole level E_(V)+0.36 eV (C_(i)-O_(i)), which is thought to act as a recombination center as well as the dominant compensating center at E_(C)-0.18 eV (B_(i)-O_(i)). As a result, the effects of lifetime degradation and carrier removal could be partially offset to higher radiation fluences by using Ga as a dopant instead of boron in Si space solar cells. The anneal out of the new hole level E_(V)+0.18 eV in gallium-doped samples at around 350℃, together with recovery of free carrier concentration, suggests that this level may act as a donor-like center which compensates free carrier concentration in gallium-doped Si.