Discrete Aln Mole Fraction Of N/12 (N=4-8) In Ga-Rich Zones Functioning As Electron Pathways Created In Nonflat Algan Layers Grown On High-Miscut Sapphire Substrates

Ga-rich zones created along macrosteps in n-AlGaN plausibly function as electron pathways of AlGaN-based deep-ultraviolet (DUV) LEDs fabricated on AlN templates using 1.0 degrees-miscut c(0001) sapphire substrates toward the m[1-100] axis. This work was performed to clarify AlN mole fractions (x(Al)) of Ga-rich zones. x(Al)similar or equal to(7/12, 6/12, and 5/12) was observed in Ga-rich zones in Al alpha Ga1-alpha N (alpha similar or equal to 0.63, 0.55, and 0.43, respectively) by the method proposed in our previous article in which we showed that Ga-rich zones of Al8/12Ga4/12N were created in Al0.7Ga0.3N. x(Al) in the Ga-rich zones obtained from an energy-dispersive x-ray signal by scanning transmission electron microscopy calibrated by Rutherford backscattering well agreed with x(Al) obtained by cross-sectional cathodoluminescence (CL) spectroscopy using scanning electron microscopy. A weak CL shoulder peak corresponding to Al4/12Ga8/12N was also observed for Al0.43Ga0.57N. In addition, x(Al)similar or equal to n/12 (n=6-9) in Al-rich zones appeared in the rest of the Ga-rich zones. Furthermore, nanobeam electron diffraction patterns of the Ga-rich zones indicated a high possibility of a regular configuration of Ga and Al atoms on the c(0001) plane in our samples. Consequently, x(Al) values in nonflat AlGaN layers with macrosteps were often determined to be near n/12 (n: integer). Thus, Ga-rich zones (x(Al)=n/12: n=4-8) formed in our nonflat AlGaN layers, which originated from the macrosteps along [11-20] edgelines normal to the m[1-100] axis, are suggested to be metastable. The creation of discrete x(Al) in Ga-rich zones should contribute to the stable production of DUV-LEDs using high-miscut sapphire substrates.