Pyramid Formation by Etching of In x Ga 1 - x N /GaN Quantum Well Structures Grown on N-face GaN for Nanooptical Light Emitters

While growth processes of In x Ga 1 - x N /GaN quantum well (QW) structures on the Ga face of GaN buffer layers are already optimized to obtain high quantum efficiency, the growth on N-face has gained momentum only in the past years. Compared with Ga face In x Ga 1 - x N layers are more stable on N face, and the surface can easily be structured by wet chemical etching, which usually leads to the formation of pyramids on the surface. This allows a new way to realize nanooptical light emitters, which offers the possibility to produce structures with similar emission properties. First, In x Ga 1 - x N /GaN (single or multi-) QW structures on N-face GaN are grown. In a second step, pyramids are formed by KOH etching. Pyramids with smooth side facets of the type ( 1 1 over bar 0 1 over bar ) are demonstrated and sharp tips in the nanometer range can be achieved without any sign of damage. Transmission electron microscopy (TEM) reveals that In x Ga 1 - x N quantum dot-like structures are present in the pyramids and in photoluminescence narrow emission lines are observed. The etching process depends on electrolyte composition and temperature, defects at the surface, and surface morphology. A better control of this process is required to achieve reproducible nanostructures.