Lateral Current Crowding in Deep UV Light Emitting Diodes over Sapphire Substrates

We report on a study of current crowding in AlInGaN multiple quantum well based deep ultra-violet light emitting diodes. For lateral geometry devices on sapphire substrates, our study concludes that the thickness and doping level of the high Al-content buffer and the cladding n -AlGaN layers is a key contributor to the lateral resistance and hence current crowding at the mesa edges. The inhomogeneous pumping of large area devices results in increased differential resistance causing a pronounced localized overheating. This degrades the device performance under high dc current operation. We also show stripe geometry to be a better choice for high power deep ultra-violet light emitting diodes on sapphire.