Transmission electron microscopy study of metamorphic III-Sb VECSELs on GaAs/AlGaAs distributed Bragg reflectors

The growth of antimonide vertical external cavity surface emitting lasers (VECSELs) for 1.8 to 2.8 μm emission wavelength is typically based on InGaAsSb/AlGaAsSb quantum wells on GaSb/AlAsSb DBRs which are in turn grown on GaSb substrates. Thus the entire structure is lattice matched to GaSb´s lattice constant of 6.09 Å. The growth of such VECSELs on GaAs/AlGaAs DBRs could be of significant advantage on account of a more mature DBR technology based on GaAs substrates, better thermal conductivity of the III-As DBRs compared to the III-Sb DBRs and better etch stop recipes for arsenide semiconductors compared to antimonides. However, the growth of such a laser would involve overcoming a 7.8% mismatch between the active region and the GaAs/AlGaAs DBR. Furthermore, the vertical cavity structure requires the quantum wells to be in very close proximity to the 7.8% mismatched GaSb/GaAs interface.¹ The challenge is therefore to reduce the threading dislocation density in the active region without a very thick metamorphic buffer or dislocation bending layers.