InGaN Nanodots Research Articles

Analysis of InGaN nanodots grown by droplet heteroepitaxy using grazing incidence small-angle X-ray scattering and electron microscopy

We present a detailed structural investigation of self-assembled indium gallium nitride nanodots grown on c-plane aluminum nitride templates by the droplet heteroepitaxy technique in a plasma-assisted molecular beam epitaxy reactor. Various growth parameters, including the total coverage of the metal species, relative and total metal effusion fluxes, and nitridation temperature were investigated. Analyses of in situ reflection high-energy electron diffraction patterns and comparison with simulations showed that the resulting crystal structure was a mixture of wurtzite and twinned zinc blende phases, with the zinc blende phase increasingly dominant for lower metal coverages and lower nitridation temperatures, and the wurtzite phase increasingly dominant for higher nitridation temperature. Studies by field emission scanning electron microscopy and atomic force microscopy revealed that the nanodots exhibit trimodal size distributions, with the dot morphologies of the intermediate size mode often resembling aggregations of distinct clusters. Nanodots grown at higher nitridation temperatures had larger inter-dot spacings, with hexagonal in-plane ordering observable at a sufficiently high temperature. Using grazing incidence small angle X-ray scattering, we determined the nanodots to be approximately truncated cone shaped, and extracted the mean radius, height, and inter-dot distance for each distribution. Microstructural investigations of the nanodots by cross-sectional transmission electron microscopy indicated that the majority of the dots were formed in dislocation-free regions, and confirmed that the intermediate size dots were approximately truncated cone shaped and consisted of both zinc blende and wurtzite regions. Mapping of the elemental distributions by energy dispersive X-ray spectroscopy in scanning transmission electron microscopy mode indicated highly nonuniform indium distributions within both small and intermediate size dots which are potentially indicative of indium clustering and kinetically controlled nanoscale phase separation rather than the spinodal decomposition associated with bulk diffusion. The observed enrichment in indium concentration towards the tops of the nanodot layers could be ascribed to the compositional pulling effect.

Origin of broad luminescence from site‐controlled InGaN nanodots fabricated by selective‐area epitaxy (Phys. Status Solidi A 3∕2014)

Origin of broad luminescence from site‐controlled InGaN nanodots fabricated by selective‐area epitaxy (Phys. Status Solidi A 3∕2014)

Origin of broad luminescence from site‐controlled InGaN nanodots fabricated by selective‐area epitaxy

We investigated the origin of broad luminescence observed from an array of site‐controlled InGaN nanodots grown by selective area epitaxy (SAE). Epitaxially grown site‐controlled nanodots with lateral dimensions <50 nm and an array density of 1010 cm−2 have been studied. During the nanoscale SAE, incorporation of adatoms from the SiO2 mask has greater relative importance, resulting in a non‐uniform growth profile. This non‐uniform growth profile leads to significant broadening of the InGaN nano‐heterostructure luminescence. Later in the SAE process, an orientation‐dependent growth rate coalesces various crystal planes and transforms these nanostructures into a more uniform array.

Growth and characterization of InGaN nanodots hybrid with InGaN/GaN quantum wells

Uniform InGaN nanodots were successfully grown on SiO2 pretreated GaN surface. It was found that the InGaN nanodots were 20 nm in diameter and 5 nm in height, approximately. After the growth of two peri- ods of InGaN/GaN quantum wells on the surface of In- GaN nanodots, nanodot structure still formed in the In- GaN well layer caused by the enhanced phase separation phenomenon. Dual-color emissions with different behavior were observed from photoluminescence (PL) spectrum of InGaN nanodots hybrid with InGaN/GaN quantum wells. A significant blueshift and a linewidth broadening were mea- sured for the low-energy peak as the increase of PL excita- tion power, while a slight blueshift and a linewidth narrow- ing occurred for the high-energy peak. Accordingly, these two peaks were assigned to be from the In-rich nanodots and quantized state transition from the InGaN/GaN quan- tum wells with indium content, respectively.

Growth and characterization of self‐assembled low‐indium composition InGaN nanodots by alternate admittance of precursors

AbstractLow‐indium composition InGaN nanodots are grown on GaN/Al2O3 by alternate admittance of triethylgallium (TEGa), trimethylindium (TMIn), and ammonia (NH3) using metalorganic vapor phase epitaxy. Since the lattice mismatch between metal (Ga, In) and GaN is large during the admittance of group III precursors and the alternate admittance of precursors can enhance the surface diffusion of adatoms, it is believed that the growth mode of InGaN nanodots is the Volmer–Weber mode. The admittance time is optimized and injecting TMIn with NH3 can increase indium composition. The ultraviolet photoluminescence spectra exhibit small temperature‐dependent redshift and a sensitive intensity change dependent on indium composition.

Photocatalysis of InGaN Nanodots Responsive to Visible Light

Photocatalysis of InGaN nanodots grown on GaN/sapphire templates by metal organic vapor phase epitaxy is studied. Photodegradation of methylene orange by InGaN nanodots responsive to visible light is observed. Analysis through atomic force microscopy and time-resolved photoluminescence measurements show that wider bandgap of InGaN, larger specific surface area and more proportion of photocarriers diffusing to the surface before recombination are propitious to photodegradation.

Self-organized InGaN nanodots grown by metal-organic chemical vapor deposition system

It has been demonstrated that self-organized InGaN nanodots can be vertically grown by utilizing metal-organic chemical vapor deposition epitaxy (MOCVD). We report the investigation of the characteristics of InGaN with various indium contents and the fabrication of self-organized InGaN nanodots will also be discussed. Using a temperature ramping growth method, self-organized InGaN nanodots were formed vertically protruding above the sample. It was found that typical height of these nanodots is around 45 nm with an average width of 5 nm. It was also found that the local density of the vertically grown self-organized InGaN nanodots could reach 8.2 × 1012 cm−2. These self-organized InGaN nanodots will result in a red shift in PL spectrum indicating that In droplets act as an indium source to form an InGaN intermediate layer near the heterointerface.

Structural and optical properties of In-rich InGaN nanodots grown by metallo-organicchemical vapor deposition

The surface morphologies, alloy compositions and emission properties of In-richInxGa1−xN nanodots (x≥0.87) grown by metallo-organic chemical vapor deposition at various growth temperatures(550–750 °C) were investigated. We found that the nucleation of InGaN dots was dominated by thesurface migration of In adatoms. A higher Ga content can be achieved at lower growthtemperatures due to the relatively lower migration ability of Ga adatoms. At higher growthtemperatures, the InGaN dots tend to decompose into In-rich islands and a thin Ga-richlayer. These In-rich islands exhibit photoluminescence emission in the near-infrared range.Another visible emission band was also observed for samples grown at higher temperatures.The formation of a thin Ga-rich layer is likely to be responsible for the visible emission.

Template-nonlithographic nanopatterning for site control growth of InGaN nanodots

A site-control nucleation and growth approach for dense InGaN nanodots has been demonstrated on the surface of GaN using a nonlithographic nanopatterning technique by metal organic chemical vapor deposition. Shallow nanopore arrays with a depth of ∼15nm are created by inductively coupled plasma etching in the GaN surface using anodic aluminum oxide films as etch masks. The nanopores are found to be the preferential sites for the InGaN nanodot formation. Uniform InGaN nanodot arrays with a density as high as 1010∕cm2 as defined by the nanopores in GaN were observed on the surface. A strong photoluminescence (PL) emission peak near 2.8eV is observed from the InGaN nanodots. The temperature dependence of PL shows the enhanced carrier localization with higher activation energy in the InGaN nanodots when compared to the InGaN thin layer grown simultaneously on the nonpatterned GaN surface.

High-density InGaN nanodots grown on pretreated GaN surfaces

High-density InGaN nanodots are successfully grown on pretreated GaN surfaces. The GaN surfaces were covered by SiO2 layers firstly, and then the SiO2 layers were removed before the growth of InGaN on the GaN. After this process, the growth of InGaN on the GaN surfaces changed to a three-dimensional mode. However, on the GaN surface without the SiO2 treatment, the growth of InGaN maintained a two-dimensional growth mode as usual. The InGaN nanodots are 26to68nm in diameter, 3.6–15nm in height, and up to 9×1010cm−2 in density, which can be controlled by growth duration and substrate temperature. Comparing with the InGaN thin film grown on untreated GaN surface with the same growth conditions, the InGaN nanodots showed stronger photoluminescence in longer wavelength range at room temperature. The formation mechanism of the nanodots is described based on the GaN surface states changed by SiO2 coverage. This approach enables fabrication of dense and controllable InGaN nanodots.

High-Density Arrays of InGaN Nanorings, Nanodots, and Nanoarrows Fabricated by a Template-Assisted Approach

Dense, crystalline arrays of InGaN nanorings, nanodots, and nanoarrows have been fabricated on GaN substrates by template-assisted nano-area selective growth. To create the nanostructures, we have used nanoporous anodic alumina films as templates to pattern nanopores in an SiO2 transfer layer, and then used this patterned SiO2 layer as a template for nitride growth by metalorganic chemical vapor deposition. We have varied the diameter of the deposited nitride nanostructures from 35 to 250 nm by changing the initial anodic alumina template structure. In addition, by controlling the nitride growth time we have created various types of nanostructures, from nanorings to nanoarrows. This structural evolution begins with the nucleation and formation of a nanoring structure, followed by coalescence and growth to form faceted nanodots, and finally lateral overgrowth to form faceted nanoarrows.

InGaN nanorings and nanodots by selective area epitaxy

An integrated process to fabricate controllable arrays of semiconductor nanorings and nanodots on patterned surfaces is presented. This approach is based on pattern transfer of nanopores to a SiO2 layer, followed by selective epitaxial growth of InGaN onto an underlying GaN substrate using metalorganic chemical vapor deposition. Using this approach, crystalline InGaN nanorings and nanodots ∼80nm in diameter have been grown on GaN surfaces. The formation mechanism of the nanorings and nanodots is described based on the initial stage of selective growth and restricted atom migration in a confined hole. Strong photoluminescence obtained at room temperature from the noncapped nanorings indicates strong confinement of the excitons in the nanostructures. This approach enables fabrication of dense, uniform arrays of epitaxial nanostructures and is potentially applicable to a variety of materials systems.