InAsSb Strain-Balanced Avalanche Photodiodes with 4-5 micron Cutoff Wavelength

Spire Corporation, through its Bandwidth Semiconductor subsidiary and in collaboration with colleagues in the Electrical Engineering Department at Boston University, proposes the metal-organic chemical vapor deposition (MOCVD) epigrowth of indium arsenide antimonide (InAsSb) avalanche photodiodes (APDs) ~2mm in diameter that should prove useful in laser radar and free-space communications. One particular composition (InAs90%Sb10%) is lattice-matched to GaSb wafers and would be used as a separate absorption region in this uncooled APD with a cutoff wavelength of about 4.4microns. The avalanche region would be in a homojunction in the higher bandgap GaSb. A thin two-compositional-step grading layer of InGaAsSb will help photogenerated carriers in the InAsSb absorption region reach the GaSb multiplication region by presenting smaller energy band transitions. This simpler lattice-matched separate absorption, grading, and multiplication region (SAGM) APD structure with a useful 4.4micron cutoff will serve as the experimental control to compare its performance with that of a strain-balanced APD using alternately tensile and compressive InAsSb layers with the goal of extending the cutoff wavelength from 4.4 to 5microns.