Growth Of InN Quantum Dots Research Articles

Controlling the size and density of InN quantum dots formed on sapphire substrate by droplet epitaxy

The growth of InN quantum dots (QDs) on c-plane sapphire by droplet epitaxy (DE) using radio frequency plasma-assisted molecular beam epitaxy is reported here. The QD growth process from liquid In droplets to the InN QDs is described with a focus on the effect ambient nitrogen from an active RF-plasma source has on the formation of In droplets as a function of substrate temperatures. The variation in the shape and size of InN QDs is explained in terms of the In atom surface diffusion and the migration of droplets. Additionally, two nitridation procedures were used to investigate the crystallization of In droplets. The droplet formation was determined to follow well known principles of nucleation theory with ripening. The resulting activation energy for In surface diffusion on sapphire was found to be 0.62 ± 0.07 eV in ultra-high vacuum, ∼10−10 Torr, and 0.57 ± 0.08 eV in ambient N2, ∼10−5 Torr. The growth of InN QDs using the DE method has many advantages over the classical Stranski–Krastanov technique, including the ability to control a wide range of QD shapes, sizes, and densities.

Self-assembled InN quantum dots on side facets of GaN nanowires

Self-assembled, atomic diffusion controlled growth of InN quantum dots was realized on the side facets of dislocation-free and c-oriented GaN nanowires having a hexagonal cross-section. The nanowires were synthesized by selective area metal organic vapor phase epitaxy. A 3 Å thick InN wetting layer was observed after growth, on top of which the InN quantum dots formed, indicating self-assembly in the Stranski-Krastanow growth mode. We found that the InN quantum dots can be tuned to nucleate either preferentially at the edges between GaN nanowire side facets, or directly on the side facets by tuning the adatom migration by controlling the precursor supersaturation and growth temperature. Structural characterization by transmission electron microscopy and reciprocal space mapping show that the InN quantum dots are close to be fully relaxed (residual strain below 1%) and that the c-planes of the InN quantum dots are tilted with respect to the GaN core. The strain relaxes mainly by the formation of misfit dislocations, observed with a periodicity of 3.2 nm at the InN and GaN hetero-interface. The misfit dislocations introduce I1 type stacking faults (…ABABCBC…) in the InN quantum dots. Photoluminescence investigations of the InN quantum dots show that the emissions shift to higher energy with reduced quantum dot size, which we attribute to increased quantum confinement.

Effects of substrate pre-nitridation and post-nitridation processes on InN quantum dots with crystallinity by droplet epitaxy

For the growth of InN quantum dots by plasma-assisted molecular beam epitaxy (PA-MBE) via droplet epitaxy technique, the effects of nitridations processes (pre-nitridation on Si (111) substrate and post-nitridation to form InN quantum dots) have been discussed in this report. Pre-nitridation and post-nitridation processes cause lots of impact to the growth mechanism of InN quantum dots. Reflected-high energy electron diffraction (RHEED) analysis can show us the in situ surface condition and assist us to observe the formation of InN quantum dots during the epitaxy. The surface conditions of Si can be modified by the substrate pre-nitridation process, the nitrogen-terminal surface could influence the sticking coefficient and surface diffusion of indium atoms. InN quantum dots with pre-nitridation process grown at temperature 450°C have relatively high dots density, broad size distribution, and shape in some preferred orientation. Meanwhile, the post-nitridation process of droplet epitaxy can reduce the dots density due to desorption, surface diffusion and aggregation phenomena. Finally, high-resolution transmission electron microscopy (HRTEM) provides the crystallinity of InN quantum dots, which is consistent with the result using RHEED. The InN quantum dots are crystallized as wurtzite structure with the lattice constant of 0.572nm. The performance of quantum dots has been investigated by photoluminescence spectra with a peak at 1530nm and a broad-peak around 1130nm.

Growth of InN quantum dots to nanorods: a competition between nucleation and growth rates

Growth evolution of InN nanostructures via a chemical vapor deposition technique is reported using In_2O_3 as precursor material and NH_3 as reactive gas in the temperature range of 550-700 ^oC. Morphology of the nanostructures solely depends on the growth temperature, evolving from quantum dot sized nanoparticles to nanorods. It is found that 630 ^oC is the threshold temperature for nanorod growth. At 630 ^oC, nucleation starts with multifaceted particle having {10-12} surface planes. Subsequently, hexagonal polyhedral NRs are grown along the [0001] direction with non-polar surfaces of m-planes {10-10}. A comprehensive study is carried out to understand the evolution of nanorods as a function of growth parameters like temperature, time and gas flow rate. Change in the morphology of nanostructures is explained based on the nucleation rate and the growth rates during the phase formation. Raman studies of these nanostructures show that a biaxial strain is developed because of unintentional impurity doping with the increase in growth temperature.

InN quantum dots on GaN nanowires grown by MOVPE

AbstractIn this work, growth of InN quantum dots (QDs) on GaN nanowires (NWs) by metal‐organic vapour phase epitaxy is demonstrated, illustrating the feasibility to combine 0D and 1D structures for nitride semiconductors. Selective area growth was used to generate arrays of c‐oriented GaN NWs using Si3N4 as the mask material. In general, InN QDs tend to form at the NW edges between the m‐plane side facets, but the QD growth can also be tuned to the side facets by controlling the growth temperature and the growth rate. TEM characterization reveals that I1‐type stacking faults are formed in the QDs and originate from the misfit dislocations at the InN/GaN interface. Photoluminescence measurement at 4 K shows that the peak shifts to high energy with reduced dot size. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Near-infrared InN quantum dots on high-In composition InGaN

We report the growth of InN quantum dots (QDs) on thick InGaN layers with high In composition (>50%) by molecular beam epitaxy. Optimized growth conditions are identified for the InGaN layers at reduced growth temperature and increased active N flux resulting in minimized phase separation and defect generation. The InN QDs grown on top of the optimized InGaN layer exhibit small size, high density, and photoluminescence up to room temperature. The InN/InGaN QDs reveal excellent potential for intermediate band solar cells with the InGaN and InN QD bandgap energies tuned to the best match of absorption to the solar spectrum.

Growth of InN quantum dots by droplet epitaxy and their characterization

AbstractDroplet epitaxy (DE) of InN quantum dots (QDs) on GaN templates using radio frequency plasma‐assisted MBE system has been reported. Two different methods of DE technique, by varying the nitridation and annealing sequence, have been employed. The various growth parameters were systematically optimized to grow non‐coalesced InN QDs without any uncrystallized In droplets. Dimensions of the QDs grown by employing the sequence of prolonged nitridation at the droplet formation temperature itself followed by annealing were found to be comparatively smaller. The differences in the crystallization of the QDs by the two methods are discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth of InN Quantum Dots on AlN/Si(111) Substrates at Various Growth Temperatures and In Molecular Fluxes

Growth of InN Quantum Dots on AlN/Si(111) Substrates at Various Growth Temperatures and In Molecular Fluxes

Indium nitride quantum dot growth modes in metalorganic vapour phase epitaxy

We have investigated growth of InN quantum dots (QDs) on GaN (0 0 0 1) in metalorganic vapour phase epitaxy as a function of growth temperature, trimethylindium partial pressure, and growth time. The growth was analysed in situ by spectroscopic ellipsometry and ex situ by X-ray diffraction and atomic force microscopy. The QDs were found for all growth temperatures between 480 °C and 600 °C and for all growth times. The density increased exponentially with decreasing growth temperature, up to 10 11 cm - 2 for 500 °C. By changing the amount of deposited material it was possible to control the size of the QDs. Above 530 °C a reduction of the effective growth rate was also observed. Reducing the V/III ratio by trimethylindium partial pressure from 15,000 to 5000 led to an increase in the growth rate. Both effects are due to reduced etching of the InN QDs by ammonia.

In situ spectroscopic ellipsometry and RHEED monitored growth of InN nanocolumns by molecular beam epitaxy

C-axis oriented InN nanocolumns (NCs) were grown on (0 0 0 1) GaN templates by molecular beam epitaxy. In situ spectroscopic ellipsometry and reflection high-energy electron diffraction demonstrated that InN NCs epitaxy was initiated from self-organized growth of InN quantum dots in Stranski–Krastanov mode, which was further confirmed by ex situ measurement of atomic force microscopy. InN NCs were of high crystal quality. The full-width at half-maximum (FWHM) value of ω-scan for (0 0 2) InN NCs showed a comparative value with that of GaN template in a range of 500–600 arcsec.

Growth of InN quantum dots on N-polarity GaN by molecular-beam epitaxy

We investigated the growth behaviors of InN quantum dots (QDs) on N-polarity GaN by molecular-beam epitaxy. The N-polarity growth has been intentionally used to raise the temperature to facilitate formation of high-quality dots. It was found that the InN QDs could be grown up to 550°C the Stranski–Kastanov growth mode with the wetting layer thickness of about 1 monolayer, which was confirmed by the simultaneous in situ observations of reflection high-energy electron diffraction and spectroscopic ellipsometry. The density and the diameter of typical InN QDs grown at 450–550°C were the order of 1011cm−2 and 15–20nm, respectively.

Growth of InN quantum dots by MOVPE

We report on comparative studies of basic properties of indium nitride quantum dots (QDs) grown by metal organic vapour phase epitaxy (MOVPE) on GaN, AlN and Si(111). Variation of the growth parameters, such as the growth temperature, deposition time, and the V/III ratio, allowed us to control characteristic sizes and a density of the QDs. With similar growth parameters, both mean height and aspect ratio of the dots are increased in a GaN, AlN, Si line. The InN QDs have been encapsulated by different materials that permit us to investigate their optical response with optical excitation, whose origin, either luminescent or scattered, is discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)