InN Dots Research Articles

Quantitative investigation of indium distribution in InN wetting layers and dots grown by metalorganic chemical vapor deposition

InN dots grown by metalorganic chemical vapor deposition were analyzed using atom probe tomography and transmission electron microscopy. A dot was found to be composed of pure InN at the core with a sharp interface with its underlying GaN layer and a more diffuse interface with its top GaN cap layer. Both techniques revealed the hexagonal truncated pyramid shape of the dots. APT has been used in the analysis of the wetting layers formed between the quantum dots. The fractional coverage appeared to saturate at longer growth times, with the highest fraction of monolayer coverage found to be 0.6.

Growth of InN/GaN dots on 4H-SiC(0001) 4° off vicinal substrates by molecular beam epitaxy

We have fabricated self-assembled InN dots on GaN using 4H-SiC(0001) vicinal substrates (4° off toward [11–20]). The size and density of InN dots were well controlled by changing the deposition amount and the growth temperature of InN. Atomic force microscope (AFM) observation revealed that the critical thickness of InN for 2D-3D transition was between 0.8 and 1.0nm. In addition, it was found that the InN dots were preferentially formed at the multistep edges on GaN. Therefore, the preparation of periodic multistep structures on GaN is considered to be an effective way to obtain highly ordered self-assembled InN dot arrays.

Optical and structural characterization of nitrogen-rich InN: Transition from nearly intrinsic to strongly n-type degenerate with temperature

We report on a detailed study of the structural and optical properties of nonstoichiometric nitrogen-rich InN grown on sapphire substrates, by migration enhanced afterglow deposition. The samples were polycrystalline, with the presence of InN dots. Unusually strong photoluminescence emission was measured at cryogenic temperatures, with the peak energy at ∼0.68 eV. Detailed analysis further shows that the sample has very low residual electron density in the range of ∼1016 cm−3 at temperatures below 20 K.

Stacked structure of self‐organized cubic InN nano‐dots grown by molecular beam epitaxy

AbstractA two‐stacked cubic (c‐) InN/c‐GaN nano‐scale dot structure is fabricated on a MgO(001) substrate by RF‐N2 molecular beam epitaxy and its microstructures are investigated by scanning transmission electron microscopy (STEM). The cubic lattice structure of InN dots is verified by STEM observations. It is implied that c‐InN dots formed on a smooth c‐GaN surface have the {111} facets. The c‐GaN cap layer has an uneven surface, which reflects the shape of the c‐InN dots embedded beneath the cap layer. InN selectively deposits in concave regions on the c‐GaN cap layer, which appear above in‐between positions of embedded dots. Thus, stacked c‐InN/c‐GaN dots do not tend to align vertically. These results open the possibility for multi‐stacking structures of c‐InN dots and their application to high‐performance optoelectronic devices based on the nitride semiconductors. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

RF-MBE growth of cubic InN nano-scale dots on cubic GaN

This paper reports the first successful growth and structural control of cubic InN (c-InN) nano-scale dots. The samples were grown on MgO (001) substrates by RF-N2 plasma molecular beam epitaxy (RF-MBE). Cubic GaN (c-GaN) underlayers with a thickness of 500nm were grown on the substrates followed by the growth of a few nm-thick InN under various conditions. The formation of InN dots aligned along the 〈110〉 directions were confirmed by atomic force microscopy (AFM). X-ray diffraction (XRD) measurements suggested the cubic zincblende lattice structure of the obtained InN dots. The area density and size of c-InN dots were well controlled by adjusting the growth conditions such as the substrate temperature and the In flux, and a very high dot density of 2.2×1011cm−2 was successfully obtained at a growth temperature of 470°C and an In flux of 7.0×10−5Pa.

Substrate impact on the growth of InN nanostructures by droplet epitaxy

AbstractThe substrate effect on InN nanostructures grown by droplet epitaxy has been studied. InN nanostructures were fabricated on Si(111), silicon nitride/Si(111), AlN/Si(111) and Ge(100) substrates by droplet epitaxy using an RF plasma nitrogen source. The morphologies of InN nanostructures were investigated by field emission scanning electron microscopy (FESEM). The chemical bonding configurations of InN nanostructures were examined by x‐ray photoelectron spectroscopy (XPS). Photoluminescence spectrum slightly blue shifted compared to the bulk InN, indicating a strong Burstein–Moss effect due to the presence of high electron concentration in the InN dots (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical and structural studies of InN/GaN dots with varying GaN cap thickness

This paper reported a structural and optical study of single InN/GaN dots with varying GaN cap thickness. The surface morphology of the 10-nm thick GaN capping layer shows a truncated pyramidal shape and changed to a dome shape when the thickness of the capping layer increases to 20-nm. The increase in compressive strain of InN dots with the increase in the cap thickness was analyzed by high resolution x-ray diffraction (HRXRD). A redshift was observed in the photoluminescence (PL) peak energy of the InN dots with increasing GaN capping thickness. The redshift of the PL peak energy of the 20-nm thick GaN capping layer sample was believed to be due to the GaN capping avoids InN decomposition and decreases the surface defect density. In addition, the maximum PL intensity of the 20-nm thick GaN capping layer sample was ∼2.5 times higher than that of the uncapped sample.

Optical Properties of Uncapped InN Nanodots Grown at Various Temperatures

Photoluminescence (PL) measurements were employed to investigate the emission properties of uncapped InN nanodot samples grown at temperature from 550 to 725 °C. Our results indicate that once the In droplets are formed, the optical properties of InN dots deteriorate markedly. As for those droplet-free samples grown at temperatures ≥600 °C, good luminescence properties are obtained. The corresponding 20 K PL peak energy is found to be almost constant at approximately 0.77 eV with a slow increase in its linewidth from 71 to 74 meV. A strong temperature-induced energy blue shift at approximately 20 to 280 K is considered to be partially connected to the band-filling effects of thermally stimulated surface electrons.

Electronic Structures of InN/GaN Quantum Dots

In this letter, ab-initio calculations are performed to study the electronic structures of the InN quantum dot embedded in the GaN matrix. By analyzing the site-decomposed densities of states, an anisotropic potential well in the dot region is clearly depicted. The In atom at the center of the quantum dot provides the highest densities of states for discrete peaks while the Ga atoms nearby In atoms also act as contributor due to hybridization. The partial charge densities distribution of conduction band minimum and valance band maximum illustrates that the charges are well localized in the InN dot region.

Investigations of photo-assisted conductive atomic force microscopy on III-nitrides

We have employed photo-assisted conductive atomic force microscopy (PA-CAFM) to obtain high-resolution current images on III-nitride surfaces. From the statistical results of current distribution, it is revealed that the full-width at half-maximum (FWHM) value is very sensitive to the dislocation density of III-nitride films even if the dislocation density is very low (∼108cm−2), suggesting that the FWHM value of current statistics can be an indicator of III-nitride quality. The results acquired by PA-CAFM are consistent with those obtained from etching-pit density and X-ray diffraction measurements. In addition, it is also revealed that PA-CAFM can observe the current distribution of InN dots without external bias influences, directly indicating the dependence of InN dots and dislocations. Our experimental results indicate that PA-CAFM is a promising method for investigating the electrical and structural properties of a nanometric area in III-nitride materials.

Fabrication of InN dot structures by droplet epitaxy using NH3

Fabrication of InN dot structures by droplet epitaxy using NH₃

Structural and optical properties of InN/GaN nanodots grown by metalorganic chemical vapor deposition

AbstractInN nanodots grown on GaN by metalorganic chemical vapor deposition (MOCVD) using conventional growth mode as well as flow‐rate modulation epitaxy (FME) at various growth temperatures (550–730 °C) were investigated. We found that different precursor injection schemes together with the effect of growth temperatures greatly influenced the surface morphology of InN dots and their photoluminescence (PL) properties. The best growth efficiency of InN was achieved by FME at around 650 °C. The residual carrier concentration and PL efficiency was also be improved when a high growth temperature was used. Our results indicated that InN nanodots can be grown at a temperature even higher than 700 °C while maintain their optical quality. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural and optical properties of cubic-InN quantum dots prepared by ion implantation in Si (100) substrate

The authors have synthesized InN quantum dots by ion implantation into a Si (100) substrate followed by a postannealing process. X-ray photoemission spectroscopy data verified the formation of In–N bonding in both as-implanted and postannealed samples. Diffraction patterns from transmission electron microscopy (TEM) confirm that the dots are of cubic crystal (zinc-blende phase) with no presence of wurtzite InN. The silicon matrix provides a constraint for the formation of the InN cubic metastable phase. However, dislocations were revealed by high resolution TEM at the interfaces between the dots and the silicon. In addition, the authors found that as the annealing temperature or time increases, dot size increases and dot density decreases. Furthermore, they demonstrate that the main emission energy of zinc-blende InN dots is about 0.736eV.

Size-dependent near-field coupling observed from InN nanodots grown on nitrided sapphire

Optical contrast from InN nanodots grown on nitrided sapphire is investigated using apertureless near-field scanning optical microscopy at two different visible wavelengths, 633 nm and 532 nm. The dependence of the near-field signal on the size of the dots is described using a coupled dipole model expanded to four dipoles. The near-field signal from InN dots with a height of <1 nm is detected due to dipole–dipole coupling.

Molecular beam epitaxy of InN dots on nitrided sapphire

A series of self-assembled InN dots are grown by radio frequency (RF) plasma-assisted molecular beam epitaxy (MBE) directly on nitrided sapphire. Initial nitridation of the sapphire substrates at 900 °C results in the formation of a rough AlN surface layer, which acts as a very thin buffer layer and facilitates the nucleation of the InN dots according to the Stranski–Krastanow growth mode, with a wetting layer of ∼0.9 nm. Atomic force microscopy (AFM) reveals that well-confined InN nanoislands with the greatest height/width at half-height ratio of 0.64 can be grown at 460 °C. Lower substrate temperatures result in a reduced aspect ratio due to a lower diffusion rate of the In adatoms, whereas the thermal decomposition of InN truncates the growth at T>500 °C. The densities of separated dots vary between 1.0×10 10 and 2.5×10 10 cm −2 depending on the growth time. Optical response of the InN dots under laser excitation is studied with apertureless near-field scanning optical microscopy and photoluminescence spectroscopy, although no photoluminescence is observed from these samples. In view of the desirable implementation of InN nanostructures into photonic devices, the results indicate that nitrided sapphire is a suitable substrate for growing self-assembled InN nanodots.

Impacts of ammonia background flows on structural and photoluminescence properties of InN dots grown on GaN by flow-rate modulation epitaxy

Structural and photoluminescence (PL) properties of InN dots grown on GaN by metal organic vapor phase epitaxy using the flow-rate modulation technique, and their dependence on growth conditions, were investigated. An ammonia (NH3) background flow was intentionally supplied during indium deposition periods to control the kinetics of adatoms and hence the morphology of InN dots. Samples prepared under lower NH3 background flows generally exhibit narrower and more intense PL signals peaked at lower emission energies. The authors point out that the NH3 background flow is an important parameter that controls not only the nucleation process but also the emission property of InN dots.

InN quantum dots grown on GaN (0001) by molecular beam epitaxy

AbstractThe growth properties of InN quantum dots on GaN (0001) surfaces by molecular beam epitaxy are being investigated. The dependence of the dimensions and density of the dots on the nucleation temperature and their evolution during growth at a constant substrate temperature are described. It is shown that both dimensions and density can be accurately controlled through nucleation temperature and deposition time. In the range from 400 °C to 450 °C, the formation of InN quantum dot structures of small dimensions and high density is feasible. InN dots with less than 3nm height, less than 22 nm diameter and with density higher than 1.7×1011 cm–2 have been obtained. Finally, vertical alignment of dots was observed for a multi‐period InN quantum dot structure in GaN matrix, grown at 430 °C. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Photoluminescence properties of self-assembled InN dots embedded in GaN grown by metal organic vapor phase epitaxy

Photoluminescence (PL) properties of InN dots embedded in GaN were investigated. We observed a systematic blueshift in the emission energy as the average dot height was reduced. The widely size-tunable emission energy can be ascribed to the size quantization effect. Temperature-dependent PL measurements show that the emission peak energies of the dots are insensitive to temperature, as compared with that of bulk film, indicating the localization of carriers in the dots. A reduced quenching of the PL from the InN dots was also observed, implying superior emission properties for the embedded InN dot structures.

Position-Controlled InN Nano-dot Growth on Patterned Substrates by ECR-MBE

ABSTRACTWe report on the growth of self-aligned InN nano-dots on nano-patterned GaN templates by electron cyclotron resonance plasma-excited molecular beam epitaxy (ECR-MBE). In the fabrication of the nano-dots, InN was grown on GaN templates with reticular patterns of holes, which were prepared by the focused ion beam (FIB) technique. The InN nano-dots were formed selectively at the holes, resulting in the reticular array of InN nano-dos. The size of InN dots was controlled by varying the hole-pitch and the growth temperature. Furthermore, the shape of InN dots improved by thermal annealing after the growth. We have succeeded in controlling the position and size of InN nano-dots on nano-patterned substrates. Typically, InN nano-dots with a diameter of 50 nm and a height of 10 nm were fabricated in 410°C growth.

RF-MBE Growth of InN Dots on N-polar GaN Grown on Vicinal c-plane Sapphire

ABSTRACTWe have grown InN quantum dots (QDs) on nitrogen-polarity (N-polarity) GaN under-layer by the radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE), and systematically investigated growth mechanism of the InN dots. The InN QDs with the N-polarity could be grown at about 500°C, which was much higher than that of previous reports on InN dots grown by MBE. When the nominal coverage of InN became more than 1 mono-layer (ML), lattice relaxation of InN occurred and high density InN dots were uniformly formed. These results indicated that InN dots were formed by Stranski-Krastanov (S-K) growth mode. For the InN deposition above about 8ML, InN dots tended to coalesce and resulted in remarakable decrease of the dots density.