Optical characterization and growth investigation of gallium-adsorbate mediated gallium nitride/aluminum nitride quantum dot heterostructures by plasma-assisted molecular beam epitaxy

The III-nitride semiconductors are attractive for a variety of electronic and optoelectronic applications, due to the large band-gap range (0.7 to 6.2 eV), high carrier mobility, and chemical stability. Spontaneous and piezoelectric polarization give rise to large internal electric fields in GaN/AlN heterostructures and are interesting for fundamental investigations and device applications. Quantum dots (QDs) are intensely studied for use as optical emitters in diverse applications ranging from quantum communications to enhancing the performance of conventional diodes and lasers because of their atomic-like density of states, enhanced free carrier capture, and tunable electronic bound states.; In this work, self-assembled GaN QDs of controlled size and density were grown and clad with AlN (0001) by plasma-assisted molecular beam epitaxy and characterized structurally by atomic force microscopy and electron microscopy. The in situ analysis techniques of line-of-sight quadrupole mass spectroscopy and reflection high-energy electron diffraction were utilized to quantify the interaction between the Ga-adsorbate bilayer and the underlying III-nitride surfaces. Fundamental investigations of GaN growth on both (0001) GaN and AlN further clarified the importance of Ga-adsorbate coverage in the mediation of epitaxial growth mode and morphology. The AlN/GaN QDs heterostructures grown in this work were characterized by photoluminescence, and optical transitions were assigned by comparison of bound state energy levels in band structure calculations for QDs and quantum wells. We demonstrate ultraviolet emission in photoluminescence experiments with GaN QDs heterostructures from 2.9 to 5.2 eV. We present a temperature dependent analysis of photoluminescence intensity, from 8 to 750 K, demonstrating the high temperature applicability of GaN QDs as potential emitters for optoelectronics device applications.