Design of nanowire-based vertical-cavity surface-emitting lasers

Abstract

The optical losses have been studied in a novel nanowire-based GaN vertical-cavity surface-emitting laser as a function of different design parameters. The simulations were based upon the finite element frequency domain method and were implemented in COMSOL Multiphysics® simulation software. The results show that the threshold material gain depends most strongly on the platelet radius. Lasers with a small platelet radii are shown to suffer from large and inevitable diffraction losses. Hence, in order to reach decent threshold material gain and achieve lasing with the current geometric design, the platelet radius must be increased to at least 1200nm to 1300nm. Additional diffraction losses derive from the pitched top of the platelet, but these can be suppressed by depositing a concave top distributed Bragg reflector (DBR) with focusing abilities. The threshold material gain can be further reduced by some extent by adding additional mirror pairs in the top DBR. Furthermore, the thickness and materials of the cladding layer also strongly affects the threshold material gain. However, the influence of the cladding layer is clearly different between having a flat top DBR or a concave top DBR. This complex influence of the cladding layer requires further investigation. The method presented has been proven robust, and comparable results to a beam propagation method (BPM) validates its accuracy. Being far less computationally heavy than BPM, it will be an important tool in the future design of novel lasers.