A study of MBE growth-related defects in InAs/GaSb type-II supperlattices for long wavelength infrared detectors

The performance of focal plane arrays type-II InAs/GaSb superlattices (T2SL) based photo-detectors is limited by their operability (percentage of working pixels). Using preferential chemical etching we formed pits around “killer” defects found in InAs/GaSb T2SL epi-layers grown by MBE on GaSb (100). These pits were then studied with various microscopically methods, including optical, high resolution scanning electron (HRSEM), high resolution transmission electron (HRTEM), and cross-section scanning tunneling (XSTM) microscopies. We have found that these “killer” defects are related to both growth conditions and substrate imperfections. Adjusting these parameters allowed us to reduce “killer” defects density by several orders of magnitude. HRTEM inspection of the defects shows that at high growth temperatures they originate close to the T2SL-GaSb interface, and develop in size during only few SL loops to a straight and narrow “column” through the whole structure. At low growth temperatures most of them are nucleated on stacking fault defects formed on irregularities in the substrate surface.