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 (
\lambda_{L} \approx 780
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 (
S \lsim 4000
cm/s) due to carrier loss in the highly Ge-doped p-Ga
0.55
Al
0.45
As cladding layer. The chemical width
W\min{90}\max{10}
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
J_{th}(T) = J_{0} \exp (T/T_{0})
improve significantly with abrupt junctions. From this material 5 μm proton-bombarded stripe lasers with a threshold current of ∼90 mA and a
T_{0} = 120
K at 780 nm have been fabricated.