III-V Nanowires for Optoelectronics

Self-Regulated Radius of Spontaneously Formed GaN Nanowires in Molecular Beam Epitaxy

Spontaneously formed GaN and ZnO nanowires (NWs) have attracted great interest for the fabrication of a wide variety of devices because they exhibit a high crystal quality independent of the substrate used for growth. However, the development of NW based GaN and ZnO devices is hampered by the incomplete understanding of the physical mechanisms governing the spontaneous growth of NWs and the resulting lack of control of their morphological properties.

Figure 1 (a) Cross-sectional scanning electron micrograph of a GaN NW array overgrown using a higher Ga flux. As shown in (b), due to the increase in the Ga flux, the NW radius continuously increases until reaching a certain equilibrium value.

 

We investigated the axial and radial growth of GaN NWs upon a variation of the Ga flux during molecular beam epitaxial growth. An increase in the Ga flux promotes radial growth without affecting the axial growth rate. In contrast, a decrease in the Ga flux reduces the axial growth rate without any change in the radius. These results are explained by a kinetic growth model that accounts for both the diffusion of Ga adatoms along the side facets toward the NW tip and the finite amount of active N available for the growth. The model explains the formation of a new equilibrium NW radius after increasing the Ga flux and provides an explanation for two well-known but so far not fully understood experimental facts: the necessity of effectively N-rich conditions for the spontaneous growth of GaN NWs and the increase in NW radius with increasing III/V flux ratio.    

 

Consequently, the results presented here provide a guide for modifying in situ the morphological properties of group-III nitride NW heterostructures. They furthermore demonstrate that to fully understand the diffusion-induced growth of compound semiconductor NWs it is necessary to consider the actual finite amount of the element that is present in abundance.

Publication
1 Author S. Fernández-Garrido , V. M. Kaganer , K. K. Sabelfeld , T. Gotschke , J. Grandal , E. Calleja , L. Geelhaar , O. Brandt
Title

Self-regulated radius of spontaneously formed GaN nanowires in molecular beam epitaxy

Source Nano Lett. , 13 , 3274 ( 2013 )
2410 Cite : Bibtex RIS
S. Fernández-Garrido, V. M. Kaganer, K. K. Sabelfeld, T. Gotschke, J. Grandal, E. Calleja, L. Geelhaar, and O. Brandt

Contact

Dr. Lutz Geelhaar

Head of Department

+49 30 20377-359

geelhaar@pdi-berlin.de

Dr. Oliver Brandt

Senior Scientist

+49 30 20377-332

lab: -444

brandt@pdi-berlin.de