Real-time x-ray studies of gallium nitride nanodot formation by droplet heteroepitaxy

Journal Article · Mon Oct 01 04:00:00 EDT 2007 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.2786578· OSTI ID:21062124

Yiyi, Wang; Oezcan, Ahmet S; Sanborn, Christopher; Ludwig, Karl F; Bhattacharyya, Anirban; Chandrasekaran, Ramya; Moustakas, Theodore D; Lin, Zhou; Smith, David J ^[1]

---

1. Physics Department, Boston University, Boston, Massachusetts 02215 (United States)

Self-organized gallium nitride nanodots have been fabricated using droplet heteroepitaxy on c-plane sapphire by plasma-assisted molecular beam epitaxy at different substrate temperatures and Ga fluxes. Nanoscale Ga droplets were initially formed on the sapphire substrate at high temperatures by Ga deposition from an effusion cell in an ultrahigh vacuum growth chamber. Subsequently, the droplets were converted into GaN nanodots using a nitrogen plasma source. The process was monitored and controlled using real-time grazing-incidence small-angle x-ray scattering. The samples were examined postgrowth by in situ grazing incidence x-ray diffraction and reflection high-energy electron diffraction, which confirmed the epitaxial relationship between the GaN nanodots and the sapphire surface. X-ray diffraction indicated that the wurtzite phase was dominant at higher substrate temperature (710 deg. C), but a mixture of wurtzite and zinc blende phases was present at a substrate temperature of 620 deg. C. Ex situ atomic force microscopy and transmission electron microscopy analyses showed that the dot size distribution was bimodal. A thin GaN continuous layer of {approx} three monolayers thick was observed by transmission electron microscopy on the sample grown at a substrate temperature of 620 deg. C, but no such layer was observed for the substrate temperature of 710 deg. C. This suggests that there is little mobility of Ga atoms in contact with the sapphire substrate at the lower temperature so that they cannot easily diffuse to nearby droplets and instead form a thin layer covering the surface.

• OSTI ID: 21062124
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 7 Vol. 102; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ATOMIC FORCE MICROSCOPY
CRYSTAL GROWTH
DEPOSITION
DROPLETS
ELECTRON DIFFRACTION
GALLIUM NITRIDES
MOLECULAR BEAM EPITAXY
NITROGEN
PLASMA
QUANTUM DOTS
SAPPHIRE
SEMICONDUCTOR MATERIALS
SMALL ANGLE SCATTERING
SUBSTRATES
TEMPERATURE RANGE 0400-1000 K
THIN FILMS
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION
ZINC SULFIDES