Nanovoid-driven highly crystalline aluminum nitride and its application in solar-blind UV photodetectors

Abstract

While aluminum nitride (AlN) is at the heart of next-generation optoelectronic applications, the growth of highly crystalline AlN remains a challenge. We investigated the formation of nanovoids (NVs) in AlN crystals and the concomitant effect on the structural and optoelectronic characteristics of AlN crystal layers. Surface treatment with a H₃PO₄ acid solution etched the initial AlN layer and as-deposited template to introduce NVs between the initial and subsequent AlN layers, and at the interfaces between the epitaxial layers and substrate during AlN regrowth. This approach suppressed the propagation of threading dislocations to the surface, thus promoting the growth of highly crystalline AlN materials. Raman spectroscopy analysis revealed that the residual stresses in AlN films were relaxed by the formation of nanovoids. UV-visible spectrometer analysis confirmed that the regrown AlN had an optical bandgap of 6.08 eV and could be suitable for use in a solar-blind UV photodetector. Furthermore, a metal–semiconductor–metal (MSM) photodetector fabricated on AlN crystals regrown on a template, acid-etched with nanovoids, showed improved photoresponse characteristics and solid solar-blind UV photodetector capability, compared to a MSM fabricated on AlN crystals regrown on an untreated template. We expect that our research will support and promote further development of group-III nitride materials and optoelectronic devices with excellent structural properties.