Thermal degradation of InGaN/GaN LEDs ohmic contacts

This paper reports an analysis of the high temperature degradation of GaN-based LEDs. It is shown that exposure to high temperatures implies (i) the decrease of the emitted optical power, (ii) the crowding of the emission profile around the central pad and (iii) the increase of the operating voltage of the devices. Degradation is attributed to the interaction between the PECVD SiN passivation layer and the ohmic contacts at the surface of the devices: by means of the Transmission Line Method the degradation of the p-side contacts is analyzed in detail. It is shown that high temperature treatment implies the increase of the contact resistivity of the metal/semiconductor (M/S) interface, and a slight variation of the sheet resistance of the semiconductor layer: these processes are responsible for the emission crowding and efficiency decay measured as a consequence of stress on the LEDs. Finally, it is shown that the described degradation process is reversible, after passivation removal and subsequent annealing.