InN Nanostructures Research Articles

Photoemission and low energy electron microscopy study on the formation and nitridation of indium droplets on Si (111)7 × 7 surfaces

The formation and nitridation of indium (In) droplets on Si (111)7×7, with regard to In droplet epitaxy growth of InN nanostructures, were studied using a spectroscopic photoemission and low energy electron microscopy, for the In coverages from 0.07 to 2.3 monolayer (ML). The results reveal that the In adatoms formed well-ordered clusters while keeping the Si (111)7×7 surface periodicity at 0.07ML and a single 3×3 phase at 0.3ML around 440–470°C. At 0.82ML, owing to the presence of structurally defect areas beside the 7×7 domains, 3-D In droplets evolved concomitantly with the formation of 4×1-In cluster chains, accompanied by a transition in surface electric property from semiconducting to metallic. Further increasing the In to 2.3ML led to a moderate increase in number density and an appreciable lateral growth of the droplets, as well as the multi-domain In phases. Upon nitridation with NH3 at ~480°C, besides the nitridation of the In droplets, the N radicals also dissociated the InSi bonds to form SiN. This caused a partial disintegration of the ordered In phase and removal of the In adatoms between the In droplets.

Chemical vapor deposition growth of InN nanostructures: Morphology regulation and field emission properties

The facile synthesis of InN nanostructures is of great importance due to their wide potential applications in (opto)electronic devices. Herein we reported the synthesis of InN nanostructures through a convenient chloride-sourced chemical vapor deposition method with simple processing and free of catalyst. The morphologies of the InN products were regulated from one-dimensional nanocones and hexagonal nanoprisms to octahedrons and four-fold-symmetrical InN hierarchical nanostructures by varying the vaporization temperature of InCl3 and deposition temperature. The formation mechanism of the InN nanostructures has been discussed on the basis of the change in InCl3 vapor pressure and the morphological evolution under different temperature. The field emission properties of the InN nanocones were evaluated due to their unique sharp apex geometry, which showed a turn on field of ∼12V/μm, suggesting their potential application in field emission devices.

Controllable Growth of InN Nanostructures

In this review, we take a survey of synthesis approaches and growth mechanisms of one-dimensional (1D) InN nanostructures in a controlled manner. InN nanostructures with hexagonal wurtzite single-crystalline structures using chemical vapor deposition (CVD) technique are discussed herein. Firstly, we attempt to overview novel growth approaches for a controllable synthesis of InN nanostructures, focusing on vapor–liquid–solid (VLS) and vapor–solid (VS) mechanisms with different starting materials. In second section, we address the factors influencing InN growth directions, including � 0001� , � 10¯� and � 0¯ 111� . Finally, we present a systematically analysis of intriguing morphologies such as nanowires, nano-cones, and crystallites with a great yield.

Regularly branched InN nanostructures: zinc-blende nanocore and polytypic transition

Regularly branched InN nanostructures were controllably grown onc-plane sapphire substrates by using hydride vapor phase epitaxy. On the basis of the crystallographic analysis of these InN tetrapods, it is proposed that (i) each tetrapod consists of four nanorods in the wurtzite phase protruding from a truncated tetrahedral nanocore in the zinc-blende phase and that (ii) branching occurs at the four {111} faces of the truncated tetrahedral nanocore. Our work suggests that the branching regularity of InN tetrapods is attributed to the polytypic transition at these four faces.

Fabrication of a‐plane InN nanostructures on patterned a‐plane GaN template by ECR‐MBE

Abstracta‐plane InN nanostructures were fabricated on a hole‐patterned a‐plane GaN template by electron‐cyclotron‐resonance plasma‐excited molecular beam epitaxy (ECR‐MBE). The growth temperature should be optimized to realize precise nucleation at the patterned holes with sufficient In desorption and a sufficiently long In migration length. Polarity determination clearly revealed that a‐plane InN crystals have an anisotropic growth morphology. The InN growth rate in the N‐polar [000–1] direction is higher than those in the In‐polar [0001] and [1–100] directions. a‐plane InN nanowalls were fabricated by exploiting the different the growth rates in the 〈0001〉 and 〈1–100〉 directions.magnified image SEM image of position‐controlled a‐plane InN nanostructures grown by ECR‐MBE on a hole‐patterned a‐plane GaN template.

Comparative studies on photovoltaic performance of InN nanostructures/p-Si(100) heterojunction devices grown by molecular beam epitaxy

ABSTRACTComparative studies have been carried out on the performance of the photovoltaic devices with dissimilar shapes of the InN nanostructures fabricated on p-Si (100). The devices fabricated with the nanodots show a superior performance compared to the devices fabricated with the nanorods. The discussions have been carried out on the superior junction property, larger effective junction area and inherent random pyramidal topographical texture of the cell fabricated with nanodots. Such single junction devices exhibit a promising fill factor and external quantum efficiency of 38% and 27%, respectively, under concentrated AM1.5 illumination.

Growth of Position-Controlled InN Nanostructures by MBE(<Special Issue>Breakthrough in Nitride Crystal Growth for Next Generation Devices)

Growth of Position-Controlled InN Nanostructures by MBE(<Special Issue>Breakthrough in Nitride Crystal Growth for Next Generation Devices)

Catalyst‐free growth of InN nanorods by metal‐organic chemical vapor deposition

AbstractWe demonstrated the growth of catalyst‐free InN nanostructures including nanorods on (0001) Al2O3 substrates using metal‐organic chemical vapor deposition. As the growth time increased, growth rate along c‐direction increased superlinearly with decreasing c‐plane area fractions and increasing side wall areas. It was also found that desorption from the sidewalls of InN nanostructures during the InN nanorods formation was one of essential key parameters of the growth mechanism. We propose a growth model to explain the InN nanostructure evolution by considering the side wall desorption and re‐deposition of indium at top c‐plane surfaces.

Formation and microstructural characterization of In 2O 3 sheath layer on InN nanostructures

An In 2O 3 sheath layer was formed on an InN nanostructure by a rapid thermal oxidation process. Rounding and bursting phenomena were observed as the progression of the oxidation process was followed. InN/In 2O 3 core-shell structures were identified as intermediate structures. After a 20 min oxidation, the InN nanostructures were completely transformed to an In 2O 3 phase. InN and In 2O 3 had wurtzite (WZ) and body-centered cubic (BCC) structures, respectively. The preferred orientation relationship of <1 1 2 ¯ 0> WZ//<1 1 0> BCC and {0 0 0 1} WZ//{ 1 ¯ 1 1} BCC was observed between InN and In 2O 3. Cracks in burst nanostructures were generated at the corners and penetrated along the <1 1 2 ¯ 0> directions.

Effects of GaN capping on the structural and optical properties of InN nanostructures grown by MOCVD

Inn nanostructures with and without gan capping layers were grown by using metal-organic chemical vapor deposition. morphological, structural, and optical properties were systematically studied by using atomic force microscopy, x-ray diffraction (xrd) and temperature-dependent photoluminescence (pl). xrd results show that an ingan structure is formed for the sample with a gan capping layer, which will reduce the quality and the ir pl emission of the inn. the lower emission peak at similar to 0.7 ev was theoretically fitted and assigned as the band edge emission of inn. temperature-dependent pl shows a good quantum efficiency for the sample without a gan capping layers; this corresponds to a lower density of dislocations and a small activation energy.

Effects of growth temperature on the optical properties of InN nanostructures grown by MOCVD

AbstractThe non‐intentionally doped InN nanostructures with different sizes were grown by metal‐organic chemical vapor deposition at different temperatures. Atomic force microscope images show that the structure of InN nanostructures sample is hexagonal with a height of 33.6, 52.5 and 132.6 nm for sample A to C, which corresponding to the growth temperature of 475, 500 and 525 °C, respectively. The height of wetting layers decided by the air‐bearing surface (ABS) analysis is 3.8, 5.8 and 16.0 nm for sample A to C, respectively. The main emission peak at 12 K for sample A to C is 0.806, 0.760 and 0.755 eV, respectively, which is related to the height of wetting layer and size of nanostructures. By the best theoretical fitting of the main emission peaks, an almost same band‐gap value of 0.712 eV with an error 0.001 eV is obtained. The difference of main emission energy and the band gap energy was caused by the recombination of degenerate electrons with photo‐holes near the top of the valence band (Burstein‐Moss effect) together with the quantum confinement effect. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Self-assembled flower-like nanostructures of InN and GaN grown by plasma-assisted molecular beam epitaxy

Nanosized hexagonal InN flower-like structures were fabricated by droplet epitaxy on GaN/Si(111) and GaN flower-like nanostructure fabricated directly on Si(111) substrate using radio frequency plasma-assisted molecular beam epitaxy. Powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study the crystallinity and morphology of the nanostructures. Moreover, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) were used to investigate the chemical compositions and optical properties of nano-flowers, respectively. Activation energy of free exciton transitions in GaN nano-flowers was derived to be ∼28.5 meV from the temperature dependent PL studies. The formation process of nano-flowers is investigated and a qualitative mechanism is proposed.

Phase mapping of aging process in InN nanostructures: oxygen incorporation and the roleof the zinc blende phase

Uncapped InN nanostructures undergo a deleterious natural aging process at ambientconditions by oxygen incorporation. The phases involved in this process and theirlocalization is mapped by transmission electron microscopy (TEM)-related techniques. Theparent wurtzite InN (InN-w) phase disappears from the surface and gradually forms ahighly textured cubic layer that completely wraps up a InN-w nucleus which still remainsfrom the original single-crystalline quantum dots. The good reticular relationships betweenthe different crystals generate low misfit strains and explain the apparent easiness for phasetransformations at room temperature and pressure conditions, but also disable the classicalmethods to identify phases and grains from TEM images. The application of thegeometrical phase algorithm in order to form numerical moiré mappings and RGBmultilayered image reconstructions allows us to discern among the different phasesand grains formed inside these nanostructures. Samples aged for shorter timesreveal the presence of metastable InN:O zinc blende (zb) volumes, which actas the intermediate phase between the initial InN-w and the most stable cubicIn2O3 end phase. These cubic phases are highly twinned with a proportion of 50:50 between bothorientations. We suggest that the existence of the intermediate InN:O-zb phase should beseriously considered to understand the reason for the widely scattered reportedfundamental properties of thought to be InN-w, as its bandgap or superconductivity.

Novel InN/InGaN multiple quantum well structures for slow‐light generation at telecommunication wavelengths

AbstractThe third order susceptibility is responsible for a variety of optical non‐linear phenomena ‐ like self focusing, phase conjugation and four‐wave mixing ‐ with applications in coherent control of optical communication. InN is particularly attractive due to its near‐IR bandgap and predicted high nonlinear effects. Moreover, the synthesis of InN nanostructures makes possible to taylor the absorption edge in the telecomunication spectral range and enhance nonlinear parameters thanks to carrier confinement. In this work, we assess the nonlinear optical behavior of InN/InxGa(1‐x)N (0.9 &gt; x &gt; 0.7) multiple‐quantum‐well (MQW) structures grown by plasma‐assisted MBE on GaN‐on‐sapphire templates. Low‐temperature (5 K) photoluminescence measurements show near‐IR emission whose intensity increases with the In content in the barriers, which is explained in terms of the existence of piezoelectric fields in the structures. The nonlinear optical absorption coefficient, α2, were measured at 1.55 μm using the Z‐scan method. We observe a strong dependence of the nonlinear absorption coefficient on the In content in the barriers. Saturable absorption is observed for the sample with x = 0.9, with α2 ∼ ‐9 x 103 cm/GW. For this sample, an optically controlled reduction of the speed of light by a factor S ∼ 80 is obtained at 1.55 μm (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Experimental observation of ferromagnetism evolution in nanostructured semiconductor InN

Recently, undoped semiconductors have been pushed to the frontiers of diluted magnetic semiconductors (DMSs) since no spurious ferromagnetism (FM) signal from metal segregation occurs. However, some aspects still remain untouched in undoped semiconductors nanostructures, including: 1) the evolution of spin moments during the fabrication process; 2) possible intrinsic relationship between the magnetic properties and morphological features, the latter being also dependent on formation process. In this article, we synthesized undoped InN nanostructures and observed a gradual magnetic transition from diamagnetic to FM, and an obvious morphology evolution from tube-shape to wire-shape products with the increase of nitridation time. It is speculated that increasing surface defects such as N vacancies in the morphology transition process are the intrinsic causes for the enhanced FM order with increase of nitridation time. The results provide some useful clues in understanding the true magnetic origin in nanostructured DMSs and reported properties inconsistencies in nanostructured materials.

Microstructural properties and initial growth behavior of InN nanobats grown on a Si(1 1 1) substrate

Bat-like InN nanostructures were successfully grown on GaN/AlN/Si(1 1 1) substrates using molecular beam epitaxy method. The initial growth behavior and structural properties of InN nanobats were studied from a nanostructural point of view. During the initial stage of the growth, a nucleation process and a shape-decision process took place in which 3-dimensional (3-D) GaN nanoislands and nanorods were formed on AlN initiation layer/Si substrate. This was followed by the independent growth of 3-D InN nanoislands and nanorods. Lateral expansion of the InN nanobats was observed, and the diameter of InN bats then reached a fixed value.

Probing Nucleation Mechanism of Self-Catalyzed InN Nanostructures

The nucleation and evolution of InN nanowires in a self-catalyzed growth process have been investigated to probe the microscopic growth mechanism of the self-catalysis and a model is proposed for high pressure growth window at ~760 Torr. In the initial stage of the growth, amorphous InNx microparticles of cone shape in liquid phase form with assistance of an InNx wetting layer on the substrate. InN crystallites form inside the cone and serve as the seeds for one-dimensional growth along the favorable [0001] orientation, resulting in single-crystalline InN nanowire bundles protruding out from the cones. An amorphous InNx sheath around the faucet tip serves as the interface between growing InN nanowires and the incoming vapors of indium and nitrogen and supports continuous growth of InN nanowires in a similar way to the oxide sheath in the oxide-assisted growth of other semiconductor nanowires. Other InN 1D nanostructures, such as belts and tubes, can be obtained by varying the InN crystallites nucleation and initiation process.

Nonpolar growth and characterization of InN overlayers on vertically oriented GaN nanorods

Nanostructured hexagonal InN overlayers were heteroepitaxially deposited on vertically oriented c-axis GaN nanorods by metal-organic chemical vapor deposition. InN overlayers grown in radial directions are featured by a nonpolar heteroepitaxial growth mode on GaN nanorods, showing a great difference from the conventional InN growth on (0001) c-plane GaN template. The surface of InN overlayers is mainly composed of several specific facets with lower crystallographic indices. The orientation relationship between InN and GaN lattices is found to be [0001]InN∥[0001]GaN and [11̱00]InN∥[11̱00]GaN. A strong photoluminescence of InN nanostructures is observed.

When group-III nitrides go infrared: New properties and perspectives

Wide-band-gap GaN and Ga-rich InGaN alloys, with energy gaps covering the blue and near-ultraviolet parts of the electromagnetic spectrum, are one group of the dominant materials for solid state lighting and lasing technologies and consequently, have been studied very well. Much less effort has been devoted to InN and In-rich InGaN alloys. A major breakthrough in 2002, stemming from much improved quality of InN films grown using molecular beam epitaxy, resulted in the bandgap of InN being revised from 1.9 eV to a much narrower value of 0.64 eV. This finding triggered a worldwide research thrust into the area of narrow-band-gap group-III nitrides. The low value of the InN bandgap provides a basis for a consistent description of the electronic structure of InGaN and InAlN alloys with all compositions. It extends the fundamental bandgap of the group III-nitride alloy system over a wider spectral region, ranging from the near infrared at ∼1.9 μm (0.64 eV for InN) to the ultraviolet at ∼0.36 μm (3.4 eV for GaN) or 0.2 μm (6.2 eV for AlN). The continuous range of bandgap energies now spans the near infrared, raising the possibility of new applications for group-III nitrides. In this article we present a detailed review of the physical properties of InN and related group III-nitride semiconductors. The electronic structure, carrier dynamics, optical transitions, defect physics, doping disparity, surface effects, and phonon structure will be discussed in the context of the InN bandgap re-evaluation. We will then describe the progress, perspectives, and challenges in the developments of new electronic and optoelectronic devices based on InGaN alloys. Advances in characterization and understanding of InN and InGaN nanostructures will also be reviewed in comparison to their thin film counterparts.

Growth of InN films and nanostructures by MOVPE

Since a few years, a lot of research efforts have been devoted to InN, the least known of the semiconducting group-III nitrides. Most of the samples available today have been grown using the molecular beam epitaxy technique, and fewer using the metal organic vapor phase epitaxy (MOVPE) method. Whatever the method, the growth of InN is extremely challenging, in particular due to the fact that no lattice matched substrate is available. This paper present results on the improvement of the InN crystal quality in MOVPE. In particular, the use of carbon halides to enhance the lateral growth is demonstrated, leading to extremely smooth InN surfaces. A new process for the realization of InN nanostructures by recrystallization is presented, which allows to obtain a better crystal quality than direct MOVPE growth.