Whispering-gallery mode InGaN microdisks on GaN substrates.

Microdisks fabricated with III-nitride materials grown on GaN substrates are demonstrated, taking advantage of the high material quality of homoepitaxial films and advanced micro-fabrication processes. The epitaxial structure consists of InGaN/GaN multi-quantum wells (MQWs) sandwiched between AlGaN/GaN and InAlN/GaN superlattices as cladding layers for optical confinement. Due to lattice-matched growth with low dislocations, an internal quantum efficiency of ∼40% is attained, while the sidewalls of the etched 8 µm-diameter microdisks patterned by microsphere lithography are optically smooth to promote the formation of whispering-gallery modes (WGMs) within the circular optical cavities. Optically pumped lasing with low threshold of ∼5.2 mJ/cm2 and quality (Q) factor of ∼3000 at the dominant lasing wavelength of 436.8 nm has been observed. The microdisks also support electroluminescent operation, demonstrating WGMs consistent with the photoluminescence spectra and with finite-difference time-domain (FDTD) simulations.

The microstructure, local indium composition and photoluminescence in green-emitting InGaN/GaN quantum wells.

In this work, we analyse the microstructure and local chemical composition of green-emitting Inx Ga1-x N/GaN quantum well (QW) heterostructures in correlation with their emission properties. Two samples of high structural quality grown by metalorganic vapour phase epitaxy (MOVPE) with a nominal composition of x = 0.15 and 0.18 indium are discussed. The local indium composition is quantitatively evaluated by comparing scanning transmission electron microscopy (STEM) images to simulations and the local indium concentration is extracted from intensity measurements. The calculations point out that the measured indium fluctuations may be correlated to the large width and intensity decrease of the PL emission peak.

Selective area growth of AlN/GaN nanocolumns on (0001) and (11-22) GaN/sapphire for semi-polar and non-polar AlN pseudo-templates.

Despite the strong interest in optoelectronic devices working in the deep ultraviolet range, no suitable low cost, large-area, high-quality AlN substrates have been available up to now. The aim of this work is the selective area growth of AlN nanocolumns by plasma assisted molecular beam epitaxy on polar (0001) and semi-polar (11-22) GaN/sapphire templates. The resulting AlN nanocolumns are vertically oriented with semi-polar {1-103} top facets when grown on (0001) GaN/sapphire, or oriented at 58° from the template normal and exposing {1-100} non-polar top facets when growing on (11-22) GaN/sapphire, in both cases reaching filling factors ≥80%. In these kinds of arrays each nanostructure could function as a building block for an individual nano-device or, due to the large filling factor values, the overall array top surfaces could be seen as a quasi (semi-polar or non-polar) AlN pseudo-template.

Filtering of Defects in Semipolar (11-22) GaN Using 2-Steps Lateral Epitaxial Overgrowth.

Good-quality (11-22) semipolar GaN sample was obtained using epitaxial lateral overgrowth. The growth conditions were chosen to enhance the growth rate along the [0001] inclined direction. Thus, the coalescence boundaries stop the propagation of basal stacking faults. The faults filtering and the improvement of the crystalline quality were attested by transmission electron microscopy and low temperature photoluminescence. The temperature dependence of the luminescence polarization under normal incidence was also studied.