Nitrides Seminar - Abdullah I. Alhassan (recent Materials alum)
3/22/2019 4PM Elings Hall 1605
Tunnel junctions (TJ) contacts in the III-Nitride light-emitting diodes (LEDs) have attracted much attention in recent years. Despite the advantages of all MBE grown TJ, metal organic chemical vapor deposition (MOCVD) grown TJ have particular attraction in III-Nitride LEDs which is more commercially viable for production. However, it is challenging to achieve an efficient TJ by MOCVD, because the as grown p-GaN layer is insulating due to hydrogen passivation, and typically activated by a postgrowth anneal. If the tunnel junction is grown by MOCVD, the hydrogen will diffuse out mainly from the sidewalls which limits the activation of buried p-GaN. One method of improving the MOCVD TJ is to allow hydrogen to diffuse vertically via opening through the top n-GaN layer.
We demonstrate high wall plug efficiency blue LEDs with tunnel junction (TJ) contacts grown entirely by MOCVD. After the growth of the LED device structure where the growth stopped at the p-GaN layer, a pattern of a dielectric is deposited on the surface of the p-GaN. Then, a selective area regrowth of n+GaN by MOCVD is performed. After etching the dielectric micropillars, a post anneal is carried out to fully activate the p-GaN through the lateral and vertical diffusion of hydrogen. In this work, we will discuss in details the effect of varying the patterns size, spacing between vias and annealing temperature on the performance of MOCVD TJ LEDs. Additionally, we explored different doping schemes to achieves high Si concentration while maintaining good surface morphology of the n++GaN layer.