Surface roughness effect on micropillar cavities

Being applied in many fields such as optoelectronics and quantum information processing, micropillar cavities are stepping into smaller and smaller scales. As a pillar is shrinking to sub-micrometer size, the surface roughness induced by imperfect fabrication process will dramatically influence the quality of such cavity, because of the edge-scattering of cavity modes. Here, we investigated this effect by using finite-difference-time-domain methods. For a micropillar cavity consisting of distributed Bragg-reflectors, the surface roughness is modeled by dividing the disk-shaped layer into a few randomly polygonal layers. One example is the investigation on the InGaAsP/InP-air-aperture micropillar cavity, which is a promised candidate for a 1.55-μm quantum-dot single-photon source. For such cavity, our results show that for short wavelength, both the Q factor and the output efficiency decrease with the increase of the surface roughness. Where, we define the surface roughness as a relative value of radius. It is worth noting that with a surface roughness of 0.01, ~1.3 nm for the InP layers and ~4.7 nm for the InGaAsP layers, the Q factor is close to 90% of the one without any roughness, which suggests that the fabrication process should satisfy a control precision at nanometer level, in order to make a micropillar cavity with good quality.