Fig. 4

Purcell factor for a source in the centre of the spacer layer, in a Bragg cavity (a,b) or uniform (c,d) pillar for a constant pillar diameter of 1.85 μm, as function of an additional GaAs layer added to the top of the pillar. In (a,c) only the emission through the top and bottom monitors \(\:{T}_{+z}\) and \(\:{T}_{-z}\) are considered while in (b,d) emission through all sides is considered. Red arrows indicate the positions of the cavity modes, whilst blue dashed lines highlight the gradients of some broad spectral features which appear in the cavity and the uniform pillar.