W-Structured Type-II Superlattice Long-Wave Infrared Photodiodes with High Quantum Efficiency

Results are presented for an enhanced type-II W-structured superlattice (WSL) photodiode with an 11.3 micron cutoff and 34% external quantum efficiency (at 8.6 microns) operating at 80 K. The new WSL design employs quaternary Al0.4Ga0.49In0.11Sb 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 microns, the authors determine that the minority-carrier electron diffusion length is 3.5 microns. The structures were grown on semitransparent n-GaSb substrates that contributed a 35%-55% gain in quantum efficiency from multiple internal reflections.
Published in Applied Physics Letters, v89 p053519-1-053519-3, 2006. Sponsored in part by MDA.