Influence of adatom migration on wrinkling morphologies of AlGaN/GaN micro-pyramids grown by selective MOVPE

Abstract

GaN micro-pyramids with AlGaN capping layer are grown by selective metal-organic-vapor phase epitaxy (MOVPE). Compared with bare GaN micro-pyramids, AlGaN/GaN micro-pyramids show wrinkling morphologies at the bottom of the structure. The formation of those special morphologies is associated with the spontaneously formed AlGaN polycrystalline particles on the dielectric mask, owing to the much higher bond energy of Al-N than that of Ga-N. When the sizes of the polycrystalline particles are larger than 50 nm, the uniform source supply behavior is disturbed, thereby leading to unsymmetrical surface morphology. Analysis reveals that the scale of surface wrinkling is related to the migration length of Ga adatoms along the AlGaN {1 101} facet. The migration properties of Al and Ga further affect the distribution of Al composition along the sidewalls, characterized by the µ-PL measurement.

Selective area growth of AlGaN nanopyramids by conventional and pulsed MOVPE

“…It allows, in addition, to know approximately the effective Al content at the surface of each pyramid by considering that the band gap corresponds to the emission of the band edges: 20% and 40% for nominal Al contents of 30% and 50%, respectively. For the growth of nanostructures, two main paths can be considered [13]: the first one corresponds to the 'vertical vapor phase diffusion (VVPD)'. For this case, the molecules are directly supplied from the showerhead to the substrate.…”

“…Indeed, the hexagonal pyramids grown on patterned templates can notably improve the material quality by the filtering of dislocations through the mask layer, limit the internal electric field in the quantum wells grown on semi polar planes, thus providing a better optical confinement, and improving the light extraction through the semi-polar facets [10][11][12]. High quality GaN pyramids have been successfully obtained by SAG on patterned templates using a metal organic vapor phase epitaxy (MOVPE) system [13]. However, this method does not work in a satisfactory manner for AlGaN nanopyramids due to the low surface diffusion of Al adatoms and to a high sticking coefficient leading to the formation of (Al, Ga)N based nuclei on the surface of the dielectric mask [14].…”

Controlled growth of aligned GaN nanostructures: from nanowires and needles to micro-rods on a single substrate

“…Semiconductor nanostructures, such as nanowires, [1][2][3][12][13][14][15][24][25][26][27][28][29] needles, 4-6 pyramids, 7,8,16,38 rod/pillars, 8,9,[16][17][18][19][20][21][22][23] and trumpets, 10,11 have wide applications in novel electronic devices. In comparison with the nanowire structure, [1][2][3][12][13][14][15]27,29 vertically aligned needle, rod and pyramid structures, which have a nanoscale tip and robust microscale-trunk, can bring advantages in single nano-structure devices [4][5][6] and optical coupling.…”