Direct imaging of the spectral emission characteristic of an InGaN/GaN-ultraviolet light-emitting diode by highly spectrally and spatially resolved electroluminescence and photoluminescence microscopy

The microscopic spectral emission characteristic of an InGaN/GaN double-het erostructure light-emitting diode is directly imaged by highly spectrally a nd spatially resolved scanning electroluminescence microscopy under operati on as a function of injection current density. The luminescence intensity m aps and especially the peak-wavelength scanning images provide access to th e optical quality of the final device and yield direct images of the In flu ctuations with 1 mu m spatial resolution. Indium concentrations varying fro m 6% to 9% are found in the active InGaN region of the ultraviolet diode em itting at 400 nm. While for low injection current densities the electrolumi nescence is dominated by emission from the p GaN originating from the whole accessible area, the emission from the InGaN active layer increases and ta kes over for higher injection conditions showing a strongly localized spati al emission characteristic. Correlation of the results with low-temperature scanning photoluminescence microscopy enables the identification of the un derlying recombination processes. (C) 1999 American Institute of Physics. [ S0003-6951(99)00548-3].