Efficient and Low‐Noise Extended Shortwave Photodiodes Based on PbSe Colloidal Quantum Dots with Wide Depletion Width

Recently, high‐efficiency and stable extended shortwave (eSWIR) photodiodes based on PbSe colloidal quantum dots (CQDs) is reported. Further improvements of PbSe‐based eSWIR photodiodes are still limited by the short lifetime of photogenerated carriers and high noise current in dark. In this work, the energy level alignments at the interface between the n‐type PbSe CQD active layer and the p‐type PbS CQD functional layer are optimized by doping the PbS CQDs with Ag atoms. The built‐in potential in the PbSe eSWIR photodiodes increased from 0.05 to over 0.5 V by doping Ag into the p‐type layer, which created a wider depletion width across the p‐n junction. The wide depletion width prolonged the lifetime of photogenerated carriers and suppressed the bimolecular recombination of carriers. In addition, the surface is smoother and cracks become smaller in the PbS CQD p‐type functional layer doped with Ag, which is helpful to reduce leakage current and improve carrier extraction. Finally, the photodiodes improved their external quantum efficiency under zero bias from 6.2% to 9.5%, and achieved 4.8 × 10 10 Jones room‐temperature specific detectivity at λ = 2.5 µm, which is comparable to that of commercial photodiodes based on epitaxial InGaAs (λ: 0.9–2.6 µm).