The influence of interface grading on threshold current density of (near) visible DH(Ga,Al)As lasers

The effect of interface grading around the active layer in DH (Ga, Al) As near-visible lasers ( nm) has been investigated for Ge and Sn as p- and n-type dopants. The combination of graded transition layers with a rather high Al and Ge concentration gives rise to a high effective interface recombination velocity ( cm/s) due to carrier loss in the highly Ge-doped p-Ga0.55Al0.45As cladding layer. The chemical width of the transition layers is determined by SIMS and SAES and found to range between 50 and 2.5 nm. The latter extremely steep interfaces have been grown in a novel LPE growth system. The threshold current density and its temperature sensitivity, in terms of the exponential relationship improve significantly with abrupt junctions. From this material 5 μm proton-bombarded stripe lasers with a threshold current of ∼90 mA and a K at 780 nm have been fabricated.