Measuring near-field optical distributions emitted from chip surface of photonic crystal patterned light emitting diodes

Abstract

In our study, the distribution of the near-field close to the chip surface of Photonic Crystal (PhC)-patterned GaN-based blue LED is measured with Near-field Scanning Optical Microscopy (NSOM). The blue LED has the layer structure consisted of Sapphire substrate - n-GaN - Multi Quantum Well (MQW) - p-GaN - ITO, where the PhC pattern is incorporated onto the top p-GaN layer. When the current is applied to the MQW, the light is emitted out of LED and the near-field on the surface of LED chip is picked up by the fiber probe of NSOM system. The system was made by ourselves, and the distance between the probe and the surface is controlled by shear force feedback control method using tuning fork, where lock-in amplifier was used for noise reduction and for dithering the probe.