W-structured type-Ⅱ superlattice long-wave infrared photodiodes with high quantum efficiency

摘要

Results are presented for an enhanced type-Ⅱ W-structured superlattice (WSL) photodiode with an 11.3 μm cutoff and 34% external quantum efficiency (at 8.6 μm) operating at 80 K. The new WSL design employs quaternary Al_(0.4)Ga_(0.49)In_(0.11)Sb barrier layers to improve collection efficiency by increasing minority-carrier mobility. By fitting the quantum efficiencies of a series of p-i-n WSL photodiodes with background-doped i-region thicknesses varying from 1 to 4 μm, the authors determine that the minority-carrier electron diffusion length is 3.5 μm. The structures were grown on semitransparent n-GaSb substrates that contributed a 35%-55% gain in quantum efficiency from multiple internal reflections.