Near-field spectroscopy of GaN blue light emission diode

The light emitting properties of GaN blue light diode has been characterized by near-field optical microscopy, near- field spectroscopy and conventional spectroscopy. Since the mechanism of the light mission from this material with high defect density is not yet fully understand, it is necessary to study the optical properties in conjunction with the nano-scale structure. The conventional spectroscopic methods are limited by the diffraction barrier, hence the information of the correlation of light emission and defects is not sufficient. By using near-field spectroscopy and near-field optical microscopy, we have studied the electro- emission spectrum of GaN blue diode, which is fabricated on sapphire substrate using low-pressure MOCVD epitaxy technique in our lab. The results how that the near-field spectroscopy can provide spatially resolved local spectrum of the samples surfaces with sub-wavelength resolution and hence provide a new technique to study the mechanism of light emission at nanometer scale. The dependence of light emission intensities vs. injection currents in the near- field spectra reveals the donor levels of the energy bands in GaN blue diode.