AlGaN Nanocolumns and AlGaN/GaN/AlGaN Nanostructures Grown by Molecular Beam Epitaxy

Abstract

This work reports on the characterization of hexagonal, single crystal AlGaN nanocolumns with diameters in the range of 30 to 100 nm grown by molecular beam epitaxy on Si(111) substrates. The change of the flux ratio between the Al and the total III-element controls the alloy composition. The Al composition trend versus the Al flux is consistent both with the E 2 phonon energy values measured by inelastic light scattering and the luminescence emission peaks position. High quality low dimensional AlGaN/GaN/AlGaN heterostructures with five GaN quantum discs, 2 and 4 nm thick, embedded into the AlGaN columns, were designed in order to study the quantum confinement effects.

GaN-nanowhiskers: MBE-growth conditions and optical properties

“…GaN nanocolumns with extremely good crystal quality and strong luminescence efficiency [20][21][22][23] have already been grown by MBE on different substrates. GaN nanocolumns with a wide range of heterostructure geometry and composition can be fabricated with good reproducibility [24][25][26][27]. While the whisker growth by MBE has already been established, a lot of uncertainty remains on the mechanisms driving the growth.…”

Mechanism for spontaneous growth of GaN nanowires with molecular beam epitaxy

“…Specific examples of the variety of noncatalytic nucleation conditions include seeded growth [9], growth on Si (111) [10][11][12][13][14][15][16][17][18][19][20][21][22], growth on sapphire or Si (111) [1][2][3][4][5][6][7][8], growth on Si (1 0 0) [23], growth with intentional surface nitridation [10], growth with AlN buffer layers [5,24,25] and growth without AlN buffer layers [26,27]. In Fig.…”

“…The majority of these nanowires are grown with catalyst nanoparticles, usually a metal such as Au or Ni, which enhances growth at the nanowire tip through supersaturation of reactant species within the catalyst droplet. Early observations of GaN nanowires grown with molecular beam epitaxy (MBE) were explained with a self-catalysis mechanism [1], with Ga droplets playing the role of the catalyst metal. In addition, there are a number of direct-reaction nanowire growth methods that also appear to be consistent with the propagation of the nanowires through the formation of a Ga droplet.…”

Nucleation conditions for catalyst-free GaN nanowires

“…These findings demonstrate that AlN provides an essential template for nanowire nucleation, which was earlier suggested by our study of nanocolumn formation in AlN buffer layers [11]. On the other hand, at least two other groups have reported [1,12,13] that they have found MBE nanowire growth conditions that do not require AlN buffer layers. It is likely that these discrepancies arise from differences in the substrate outgas procedures and growth system hardware (such as manipulator heater environments) that in turn affect SiN x formation in the early stages of growth.…”