Tlenkowe kontakty omowe z kryształami fotonicznymi dla wydajnych diod PCSEL opartych na GaN

(PC) laser diodes (LDs) by introducing a new concept - a transparent, conducting oxide film serving both as the PC host, the current-spreading layer and ohmic contact for the p-GaN layer. GaN LDs are multilayer epitaxial structures of high complexity and requiring considerable experience and a high technology to fabricate in device-grade quality. The main obstacle hindering their application as high power light sources is the difficulty to achieve high power density, single mode operation and low beam divergence using one of the available technologies. Recently, a new approach appeared taking advantage of the coupling of light modes between the active area of a laser diode and a photonic crystal fabricated in its vicinity. Such devices, called Photonic Crystal Surface Emitting Lasers, require submicrometer patterns to be etched in the top p-GaN layer of the GaN-based epitaxial structure. There are two important challenges related to the fabrication of PCSELs based on nitride semiconductors. The process of hole etching in the top layers of the laser may lead to severe deterioration of p-type layer electrical properties as the etching process is known to introduce donor-like defects in the etched material. If PC fabrication in the n-type GaN layer below the active area would be considered, it would require a very difficult regrowth and planarization of the structure, which is challenging for nitride semiconductor epitaxy. With these limitations in mind, we envisaged a strategy to develop a novel approach to PC fabrication in GaN-based PCSELs, utilizing a stable, transparent, highly efficient ZnO:Al (AZO) - based ohmic contact to the p-GaN film which would host the PC instead of the p- GaN film. As an outcome, no etching-induced degradation of the GaN epitaxial structure would take place, and the AZO film would at the same time work as both the PC layer and as a current-spreading layer, all of which would improve the performance of such diodes with respect to the ones with the PCs etched in the p-GaN.