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

Abstract

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 EV+0.36 eV has been identified as Ci–Oi complexes. The absence of an EC−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 Bi–Oi 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 EV+0.36 eV (Ci–Oi), which is thought to act as a recombination center as well as the dominant compensating center at EC−0.18 eV (Bi–Oi). 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 EV+0.18 eV in gallium-doped samples at around 350 °C, 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.

Characterization of defects created in Cz and epitaxial Si doped with Ga or B using Laplace-DLTS

“…A defect with energy position at 0.18 eV relative to the valence band and displaying identical annealing behaviour has previously been reported in electron-irradiated Ga-doped Cz-Si. This defect has been suggested to be a complex involving Ga i [2].…”

“…This clearly reveals that the formation of this complex is inhibited in Ga-doped Cz-Si, and is consistent with results previously reported in Refs. [2] and [3].…”

“…The lifetime degradation is not observed in Ga-doped Cz-Si [1]. However, few studies have investigated Ga-related defects in p-type Si, and detailed comparative studies of defect introduction rate of defects in B-or Ga-doped Cz-Si are not numerous [2] and [3].…”

Vacancy-oxygen defects in silicon: the impact of isovalent doping

“…C i O i is another important recombination centre in Si [6]. The phenomenon of communication between defects is very important in understanding the mechanisms of trapping and recombination of non equilibrium charge carriers at defect levels.…”

Oxygen-vacancy defects in electron-irradiated Si: the role of carbon in their behavior

“…There are many technological and fundamental research reasons that demand a detailed understanding of the VO defect properties and behavior: Firstly, the defect introduces an acceptor level [4][5][6] in the forbidden energy gap at around E c -0.17 eV. Due to its electrical activity the A-center acts as a recombination center [7,8], resulting in the deterioration of devices especially those operating in radiation environment, for instance Si detectors. Secondly, upon annealing VO interacts with oxygen impurities and vacancies leading to the formation [9] of various V n O m defects.…”