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.