Spatial inhomogeneity investigation of QW emission in InGaN MQW LEDs

The luminescence properties of InGaN multiquantum well (MQW) light emitting diodes (LEDs) with various emission wavelengths were investigated using electroluminescence (EL) microscopy (ELM) and micro-EL (μ-EL) spectroscopy. Spatial inhomogeneity of the QW emission was observed as a function of the emission wavelength in spectrally resolved ELM images. The results show that the emission from diodes with shorter emission wavelengths exhibit less spatial inhomogeneity, while bright features were observed on the surface of samples with longer emission wavelengths. μ-EL spectra obtained from 5×5 μm2 regions show an increase in the full width at half maximum (FWHM) of the spectra with increasing injection current and emission wavelength. With increasing emission wavelength, there is a shift in the main emission area from the p-contact area to the n-contact. The μ-EL spectra obtained from different bright spots in the ELM images demonstrate the variation of main emission peak position and FWHM of the EL spectra. The results suggest that the band-tailing effect due to small self-organised In-rich regions play a key role in the emission of the InGaN MQWs.