Construction of localized state levels and near-infrared light absorption of silicon: B/P doping and first-principles calculations

Abstract

Theoretically, the light wavelength that a silicon-based detector can detect is less than 1100 nm. After silicon (Si) is singly doped or co-doped with phosphorus (P) and boron (B) impurities, the localized state levels are formed in forbidden band, which makes it possible to absorb long wavelength light for the doped Si. Although the ionization energy of both P and B as shallow level impurities in Si is close to each other, the first-principles study in this paper shows that the near-infrared light absorption of n-Si is weaker than that of p-Si for the same concentration of impurities. After the impurity compensation of p-/n-Si based on P and B co-doping, the localized state levels are constructed by B− and P+ ions in the forbidden band of Si. The near-infrared absorption of n-Si can be significantly enhanced by impurity compensation, whereas the opposite case is true for p-Si. Moreover, even if p-/n-Si is fully compensated by impurities, it still has a strong near-infrared light absorption, which is different from intrinsic Si. Possible reasons on the difference of the above-mentioned light absorption were discussed.