Fe-implantation for rear-facet coatings of InP-based quantum cascade lasers

Fe-implantation is used to create a high-resistivity layer at the rear facet of an InP-based quantum cascade laser (lambda = 3.9 mu m), subsequently coated with a metallisation of Cr (5 nm) and Au (200 nm). The coatings lead to a 3.7-fold increase of front-facet power and a 20–30% reduction in threshold current density compared to uncoated lasers.