Greatly improved performance of $340nm$ light emitting diodes using a very thin GaN interlayer on a high temperature AlN buffer layer

This letter reports a simple approach to significantly improve the performance of $340nm$ ultraviolet light emitting diodes (UV-LEDs) on an AlN buffer layer. Greatly improved optical and electrical properties of the $340nm$ UV-LED have been achieved by using a very thin GaN interlayer $(10–20nm)$⁠, deposited on AlN as a buffer layer directly on sapphire prior to growth of the UV-LED structure. Compared with the UV-LED without the thin GaN interlayer, the output power of the LED with it is increased by a factor of $∼2.2$⁠, and the applied bias voltage at $20mA$ drops from $6.5to∼5V$⁠. High resolution transmission electron observation indicates that the thin GaN interlayer can effectively stop the penetration of the dislocations in the AlN buffer layer into the overlaying AlGaN layer, while most of the dislocations in the AlN buffer layer in the UV-LED without the thin GaN interlayer can propagate into the overlying AlGaN layer. Therefore, the enhanced performance of the $340nm$ UV-LEDs results from a massive reduction in dislocation density in the overlying device structure due to the very thin GaN interlayer. Since it is extremely difficult to reduce the dislocation density in an AlN layer on sapphire, the simple and reliable approach reported in this letter provides a good alternative option to prevent the propagation of dislocations from an AlN buffer into an overlying device structure.