II–VI quantum cascade emitters in the 6–8 μm range

We present the growth and characterization of ZnCdSe/ZnCdMgSe quantum cascade (QC) heterostructures grown by molecular beam epitaxy (MBE) and designed to operate at 6–8 μm. These structures utilize the better-understood ZnCdMgSe with InP lattice matched compositions yielding a bandgap of 2.80 eV as compared to previous work which used ZnCdMgSe compositions with bandgaps at 3.00 eV. Grown structures posses good structural and optical properties evidenced in X-ray diffraction and photoluminescence studies. Fabricated mesa devices show temperature dependent I–V measurements with differential resistance of 3.6 Ω, and a turn on voltage of 11 V consistent with design specifications. Electroluminescence was observed in these devices up to room temperature with emission centered at 7.1 μm and line-widths of ∼16% (ΔE/E) at 80 K. The results show that these are well-behaved electroluminescent structures. Addition of waveguide layers and further improvements in well barrier interfaces are being pursued in efforts to demonstrate lasing.