We show that the shape of GaN nanostructures grown by molecular beam epitaxy on AlxGa1−xN (0001) surfaces, for x≥0.4, can be controlled via the ammonia pressure. The nanostructures are obtained from a two dimensional to three dimensional transition of a GaN layer occurring upon a growth interruption. Atomic force microscopy measurements show that depending on the ammonia pressure during the growth interruption, dot or dash-shaped nanostructures can be obtained. Low temperature photoluminescence measurements reveal a large redshift in the emission energy of the quantum dashes, as compared to the quantum dots. By simply adjusting the GaN deposited thickness, it is shown that quantum dashes enable to strongly extend the emission range of GaN/Al0.5Ga0.5N nanostructures from the violet-blue (∼400–470 nm) to the green-orange range (∼500–600 nm).

Articles you may be interested inStark effect in ensembles of polar (0001) Al0.5Ga0.5N/GaN quantum dots and comparison with semipolar (11−22) ones J. Appl. Phys. 116, 034308 (2014); 10.1063/1.4889922 Mechanism of GaN quantum dot overgrowth by Al0.5Ga0.5N: Strain evolution and phase separation J. Appl. Phys. 111, 084309 (2012); 10.1063/1.4704682 GaN quantum dot superlattices grown by molecular beam epitaxy at high temperature Investigation of AlN films grown by molecular beam epitaxy on vicinal Si(111) as templates for GaN quantum dots Appl.Influence of AlN overgrowth on structural properties of GaN quantum wells and quantum dots grown by plasma-assisted molecular beam epitaxy

Al 1 − x In x N ternary alloys with solid phase indium compositions between x=0.15 and 0.28 have been grown by metal organic chemical vapor deposition under indium rich conditions within the growth temperature range of 750–810 °C. A thermally activated process with activation energy of 1.05±0.05eV is found to compete with indium incorporation. Smooth epitaxial layers with root mean-squares surface roughness of 0.3–0.8nm are obtained. (Al,In)N films lattice matched to GaN have been introduced into laser diode structures for optical confinement. Optical gain is observed.

The interfacial relationship and the microstructure of nonpolar (11−20) ZnO films epitaxially grown on (1−102) R-plane sapphire by molecular beam epitaxy are investigated by transmission electron microscopy. The already-reported epitaxial relationships [1−100]ZnO∥[11−20]sapphire and ⟨0001⟩ZnO∥[−1101]sapphire are confirmed, and we have determined the orientation of the Zn–O (cation-anion) bond along [0001]ZnO in the films as being uniquely defined with respect to a reference surface Al–O bond on the sapphire substrate. The microstructure of the films is dominated by the presence of I1 basal stacking faults [density=(1–2)×105cm−1] and related partial dislocations [density=(4–7)×1010cm−2]. It is shown that I1 basal stacking faults correspond to dissociated perfect dislocations, either c or a+c type.