Strong enhancement of light extraction efficiency in GaInAsP 2-D-arranged microcolumns

This paper experimentally demonstrates the strong enhancement of light extraction efficiency in two-dimensionally arranged microcolumns. They were designed like a honeycomb photonic crystal and fabricated into GaInAsP-InP wafers by using the inductively coupled plasma etching. For the laterally directed light passing through the microcolumns, peculiar transmission characteristics were observed, which could be explained by the Bragg reflection theory, namely, the photonic bandgap (PBG). The measurement of spontaneous lifetime showed that the internal efficiency in the microcolumns was reduced by the surface recombination at sidewalls. In contrast, the light extraction efficiency evaluated from the measured photoluminescence intensity, and the internal efficiency was more than ten times that for a planar wafer. This was thought to be due to the expanded escape cone of internal light by the low effective refractive index, and also due to the strong diffraction and scattering of laterally directed light, which corresponds to the second-order Bragg condition. Such effects are expected not only in photonic crystals but also in some disordered structures. We expect this structure to allow a high-efficiency light-emitting diode (LED), since electronic elements needed for current injection devices can be added independently of the effects.