Reduced peripheral leakage current in pin photodetectors of Ge on n⁺-Si by P⁺ implantation to compensate surface holes

Abstract

A reduced dark leakage current, without degrading the near-infrared responsivity, is reported for a vertical pin structure of Ge photodiodes (PDs) on n⁺-Si substrate, which usually shows a leakage current higher than PDs on p⁺-Si. The peripheral/surface leakage, the dominant leakage in PDs on n⁺-Si, is significantly suppressed by globally implanting P⁺ in the i-Si cap layer protecting the fragile surface of i-Ge epitaxial layer before locally implanting B⁺/BF₂⁺ for the top p⁺ region of the pin junction. The P⁺ implantation compensates free holes unintentionally induced due to the Fermi level pinning at the surface/interface of Ge. By preventing the hole conduction from the periphery to the top p⁺ region under a negative/reverse bias, a reduction in the leakage current of PDs on n⁺-Si is realized.