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This work reports on a chemical beam epitaxy growth study of InGaAs/GaAs quantum dots (QDs) engineered using an in-situ indium-flush technique. The emission energy of these structures has been selectively tuned over 225 meV by varying the dot height from 7 to 2 nm. A blueshift of the photoluminescence (PL) emission peak and a decrease of the intersublevel spacing energy are observed when the dot height is reduced. Numerical investigations of the influence of dot structural parameters on their electronic structure have been carried out by solving the single-particle one-band effective mass Schrodinger equation in cylindrical coordinates, for lens-shaped QDs. The correlation between numerical calculations and PL results is used to better describe the influence of the In-flush technique on both the dot height and the dot composition.

This article summarizes some of the critical features of pure indium antimonide nanowires (InSb NWs) growth and their potential applications in the industry. In the first section, historical studies on the growth of InSb NWs have been presented, while in the second part, a comprehensive overview of the various synthesis techniques is demonstrated briefly. The major emphasis of current review is vapor phase deposition of NWs by manifold techniques. In addition, author review various protocols and methodologies employed to generate NWs from diverse material systems via self-organized fabrication procedures comprising chemical vapor deposition, annealing in reactive atmosphere, evaporation of InSb, molecular/ chemical beam epitaxy, solution-based techniques, and top-down fabrication method. The benefits and ill effects of the gold and self-catalyzed materials for the growth of NWs are explained at length. Afterward, in the next part, four thermodynamic characteristics of NW growth criterion concerning the expansion of NWs, growth velocity, Gibbs–Thomson effect, and growth model were expounded and discussed concisely. Recent progress in device fabrications is explained in the third part, in which the electrical and optical properties of InSb NWs were reviewed by considering the effects of conductivity which are diameter dependent and the applications of NWs in the fabrications of field-effect transistors, quantum devices, thermoelectrics, and detectors.

III-V semiconductor heterostructures are important components of many solid-state optoelectronic devices, but the ability to control and tune the electrical and optical properties of these structures in conventional device geometries is fundamentally limited by the bulk dimensionality and the inability to accommodate lattice-mismatched material combinations. Here we demonstrate how semiconductor nanowires may enable the creation of arbitrarily shaped one-dimensional potential structures for new types of designed device functionality. We describe the controlled growth of stepwise compositionally graded InAs1-xPx heterostructures defined along the axes of InAs nanowires, and we show that nanowires with sawtooth-shaped composition profiles behave as near-ideal unipolar diodes with ratchet-like rectification of the electron transport through the nanowires, in excellent agreement with simulations. This new type of designed quasi-1D potential structure represents a significant advance in band gap engineering and may enable fundamental studies of low-dimensional hot-carrier dynamics, in addition to constituting a platform for implementing novel electronic and optoelectronic device concepts.

We report on the nucleation and growth mechanism of self-catalyzed InAs nanowires (NWs) grown on Si (111) substrates by chemical beam epitaxy. Careful choices of the growth parameters lead to In-rich conditions such that the InAs NWs nucleate from an In droplet and grow by the vapor-liquid-solid mechanism while sustaining an In droplet at the tip. As the growth progresses, new NWs continue to nucleate on the Si (111) surface causing a spread in the NW size distribution. The observed behavior in NW nucleation and growth is described within a suitable existing theoretical model allowing us to extract relevant growth parameters. We argue that these results provide useful guidelines to rationally control the growth of self-catalyzed InAs NWs for various applications.

Today, metalorganic vapor phase epitaxy (MOVPE) is the most important method for the fabrication of optoelectronic devices like light emitting diodes and laser diodes as well as for electronic devices based on compound semiconductors. In this article, we focus on the synthesis and characteristics of organometallic compounds which are used as precursors for the MOVPE of compound semiconductor heterostructures. Besides having an adequate vapor pressure, the most important requirement to such precursors is their extremely high purity. Therefore, specific synthesis routes have been established, which, in combination with sophisticated purification steps, provide material with purity levels in the sub-ppm-level. The most important organometallic precursors are the lightest molecules like Me3M, (trimethyl-metal), where ‘M’ stands for Ga, In, or Al, because they have acceptable vapor pressure and adequate chemical stability. Particularly for p-type doping of such semiconductors, specific organometallics have been developed containing the metals Zn, Mg, and others. Tert-butyl compounds for the group V elements As and P help to reduce the hazard of the extremely toxic hydrides AsH3 and PH3.

In this paper, we introduced a new different thin film deposition method for heavily carbon doped GaAs. Used method is thermionic vacuum arc (TVA) and first used for the carbon doping process. The method is very fast deposition process for the other growth method such as metal organic chemical vapor deposition, molecular beam epitaxy, molecular organic molecular beam epitaxy. The smallest grain size of GaAs and doped GaAs were obtained by carbon doping process. Mean crystalline size and height of crystalline size were found to be 3.4 nm and 4 nm, respectively. Crystal direction was found to be (022) plane and (024) plane for the sample at 45.322° and 75.060°, respectively. The production process and obtained results show that used methods is very simple, low cost, eco friendly and very fast method for the carbon doped GaAs. © 2015 Elsevier B.V.

Direct graphene growth on semiconductor substrates is an important goal for successful integration of graphene with the existing semiconductor technology. We test the feasibility of this goal by using molecular beam epitaxy on various semiconductor substrates: group IV (Si, SiC), group III–V (GaAs, GaN, InP), and group II–VI (ZnSe, ZnO). Graphitic carbon has been formed on most substrates except Si. In general, the crystallinities of carbon layers are better on substrates of hexagonal symmetry than those on cubic substrates. The flatness of graphitic carbon grown by molecular beam epitaxy is noticeable, which may help the integration with semiconductor structures.

The growth of free-standing AlAs nanowires on GaAs (111)B substrates by chemical beam epitaxy is presented. Nanowire growth was achieved by employing trimethylaluminium and tertiarybutylarsine as metal-organic precursors and Au as catalyst. Different temperature and group III partial pressure values were examined to investigate the growth mechanism. Furthermore, synthesis of a GaAs shell is proposed as a way to protect the AlAs nanowires from rapid oxidization. In situ reflection high energy electron diffraction analysis and ex situ scanning and transmission electron microscopy studies were performed on both AlAs and AlAs-GaAs core-shell nanowires in order to assess crystal perfection and structure of the nanowires.

We present investigations on InSb nanowires grown directly on InSb substrates. A chemical beam epitaxy system was used to synthesize InSb nanowires. Growth at low temperatures (300−400 °C) resulted in extensive parasitic InSb thin film deposition and stacking faults within these nanowires. To circumvent both problems, InSb nanowires were synthesized at temperatures above 410 °C. By further optimizing the growth parameters completely stacking fault-free, free-standing InSb nanowires were obtained. By combining chemical beam epitaxy and laser interference lithography, large areas of ordered InSb nanowires were fabricated. Temperature-dependent electrical measurements on these InSb nanowire arrays showed intrinsic bulklike behavior.

A nitrogen-related electron trap (E1), located approximately 0.33 eV from the conduction band minimum of GaAsN grown by chemical beam epitaxy, was confirmed by investigating the dependence of its density with N concentration. This level exhibits a high capture cross section compared with that of native defects in GaAs. Its density increases significantly with N concentration, persists following post-thermal annealing, and was found to be quasi-uniformly distributed. These results indicate that E1 is a stable defect that is formed during growth to compensate for the tensile strain caused by N. Furthermore, E1 was confirmed to act as a recombination center by comparing its activation energy with that of the recombination current in the depletion region of the alloy. However, this technique cannot characterize the electron−hole (e–h) recombination process. For that, double carrier pulse deep level transient spectroscopy is used to confirm the non-radiative e – h recombination process through E1, to estimate the capture cross section of holes, and to evaluate the energy of multi-phonon emission. Furthermore, a configuration coordinate diagram is modeled based on the physical parameters of E1.

GaAs, InAs and Ga 1− x In x As layers were grown by chemical beam epitaxy (CBE) using triethylgallium, trimethylindium and tertiarybutylarsine as precursors for Ga, In and As, respectively. The growth rate during the homoepitaxial growth of GaAs and InAs, deduced from the frequency of reflection high-energy electron diffraction intensity oscillations, was used to calibrate the incorporation rates for the III elements. The In content of the Ga 1− x In x As layers was measured by Rutherford backscattering spectrometry and compared with the value predicted from the above calibration data; while the measured In mole fraction is close to the predicted value for the samples grown for low In to Ga flux ratios ( x

In this work, we report the selective area epitaxial growth of high quality InP in shallow trench isolation (STI) structures on Si (0 0 1) substrates 6° miscut toward (1 1 1) using a thin Ge buffer layer. We studied the impact of growth rates and steric hindrance effects on the nano-twin formation at the STI side walls. It was found that a too high growth rate induces more nano-twins in the layer and results in InP crystal distortion. The STI side wall tapering angle and the substrate miscut angle induced streric hindrance between the InP facets and the STI side walls also contribute to defect formation. In the [1 1 0] orientated trenches, when the STI side wall tapering angle is larger than 10°, crystal distortion was observed while the substrate miscut angle has no significant impact on the InP defect formation. In the [1 1 0] trenches, both the increased STI tapering angle and the substrate miscut angle induce high density of defects. With a small STI tapering angle and a thin Ge layer, we obtained extended defect free InP in the top region of the [1 1 0] trenches with aspect ratio larger than 2.

Low-pressure microplasma treatment was performed to clean a substrate surface prior to the selective growth of GaN by chemical beam epitaxy. To investigate the cleaning mechanism, the process pressure and process time were systematically varied. The plasma distribution was also studied using a special sheet, whose color changes following the irradiation of plasma species. Consequently, it was found that the range of microplasma irradiation increased with decreasing process pressure, and simultaneously, the morphology of selective growth was improved. Secondary ion mass spectrometry measurements show that the oxygen concentration at the growth interface was reduced from 9.7 × 1014 to 2.6 × 1013 atoms/cm2 by the microplasma treatment. Otherwise, the surface oxides resulted in the growth of a rough surface with the suppression of the layer-by-layer growth.

We present the growth of stacked layers of InAs quantum dots directly on high bandgap In 0.68 Ga 0.32 As 0.7 P 0.3 ( λ g =1420 nm) barriers. The quaternary material is lattice matched to InP forming a double hetero-structure. Indium flux, number of InAs stacked layers and InGaAsP inner separation layer thickness were investigated. Photoluminescence (PL) and atomic force microscopy (AFM) analysis indicate the occurrence of gallium diffusion and the arsenic/phosphorus (As/P) exchange with the InGaAsP barriers. As a result, shorter wavelength emission is observed, making the structures suitable for telecom applications.

The formation of ordered InAs/InP quantum dot (QD) arrays is demonstrated on patterned InP (1 0 0) and (3 1 1)B substrates by the concept of self-organized anisotropic strain engineering in chemical beam epitaxy (CBE). On shallow- and deep stripe-patterned InP (1 0 0) substrates, depending on the stripe orientation, the linear one-dimensional InAs QD arrays are rotated away from their natural direction due to the presence of vicinal stepped sidewall planes modifying the self-organization process, coexisting with QD free steep side facets on the deep-patterned substrates. On shallow- and deep-patterned InP (3 1 1)B substrates only QD free side facets form with flat top and bottom areas, not affecting the natural ordering of the two-dimensional InAs QD arrays. On the deep-patterned substrates a row of dense QDs forms on top along the side facets due to their slow-growing behavior. The optical properties of the QD arrays on the patterned substrates are not degraded compared to those of arrays formed on planar substrates for both InP (1 0 0) and (3 1 1)B substrates showing the potential of self-organized anisotropic strain engineering combined with step engineering for the creation of advanced complex QD arrays and networks. © 2010 Elsevier B.V. All rights reserved. U7 - Export Date: 2 August 2010 U7 - Source: Scopus U7 - Article in Press

Low temperature ( < 80 °C) neutral beam deposition (LTNBD) was investigated as a new approach to the fabrication and development of nano-crystalline silicon (nc-Si), which has better properties than that of amorphous silicon (α-Si). The difference between LTNBD and conventional PECVD is that the film formation energy of the nc-Si in LTNBD is supplied by controlled neutral beam energies at a low temperature rather than by heating. Especially, in this study, the characteristics of the nc-Si thin film were investigated by adding 10% of an inert gas such as Ne, Ar or Xe to SiH 4 /H 2 . Increasing the beam energy resulted in an increase in the deposition rate, but the crystallinity was decreased, due to the increased damage to the substrate. However, the addition of a higher mass inert gas to the gas mixture at a fixed beam energy resulted not only in a higher deposition rate but also in a higher crystallization volume fraction. The high resolution transmission electron microscopy image showed that the grown film is composed of about 10 nm-size grains.

Density functional theory calculations are employed to investigate B incorporation at the GaN(0001) and AlN(0001) surfaces. It is found that under typical metal-organic chemical vapor deposition (MOCVD) and metal rich molecular beam epitaxy (MBE) conditions, the maximum B contents at the surfaces are in the order of 3% for GaN and 15% for AlN. Under MBE N-rich growth conditions the calculations reveal a rehybridization enhanced solubility mechanism that dominates at the surface. This mechanism offers a promising route to kinetically stabilize B contents above the bulk solubility limit and as high as 25%.

A discrete-continuum theory for the step-flow growth by chemical beam or metalorganic vapor-phase epitaxy of a generic binary-compound thin film is developed from basic considerations of continuum physics in accordance with the second law of thermodynamics. Our theory accounts for dissipation, chemical and otherwise; allows for departures from equilibrium; and generalizes the classical, variationally derived Gibbs–Thomson relation along the steps. In contrast to existing models, the diffusing species are coupled through a chemical reaction whereby bulk molecules are crystallized from adatoms attaching to the step edges. The linear stability analysis of the resulting free-boundary problem for a periodic train of rectilinear steps yields pairing in the presence of the normal Ehrlich–Schwoebel barrier for both species, counter to the predictions of standard Burton–Cabrera–Frank models for single-species growth. In particular, we show that the onset of step bunching occurs as long as the adatom equilibrium coverage of either species is sufficiently high, a condition met, e.g., during the epitaxy of gallium arsenide. The physical origin of this instability is to be found in the dependence of the step chemical potential on the jump in the adatom grand canonical potential, a term that couples adjacent terraces and—counter to elastic, entropic, or electrostatic interactions between steps—is attractive.

We investigated the relation between N–H complexes and the electrical properties of GaAsN, which is a potential material for fabricating super-high-efficiency multi-junction tandem solar cells. In order to separate the effect of other residual carrier such as carbon in a GaAsN film on the electrical properties, hydrogen (H) ions were implanted into GaAsN grown by chemical beam epitaxy (CBE) and then rapid thermal annealing from 250 to 650 °C was carried out. Two N–H complexes related to local vibrational modes (LVMs) in GaAsN were observed at 3098 and 3125 cm−1. With an increasing annealing temperature, the integrated peak intensity of the 3098 cm−1 peak (I3098) decreased, while that of the 3125 cm−1 peak (I3125) increased. This indicates that N–H complexes related to the 3125 cm−1 peak are thermally more stable than those related to the other peak. The hole concentrations and mobilities exhibited an increasing trend until an annealing temperature of 550 °C was reached. Their increases are attributed to the removal of donor-type defects. It is suggested that the N–H complexes related to the 3098 cm−1 peak are electrically active, while those giving the 3125 cm−1 peak are inactive.

The authors report a study of molecular beam deposition of MgO films on amorphous SiO2 and (0001) GaN surfaces over a large range of temperatures (25–400 °C) and molecular oxygen growth pressures (10−7–10−4 Torr). This study provides insight into the growth behavior of an oxide with volatile metal constituents. Unlike other materials containing volatile constituents (e.g., GaAs, PbTiO3), all components of MgO become volatile at normal epitaxial growth temperatures (≥250 °C). Consequently, defining which species is the adsorption controller becomes ambiguous. Different growth regimes are delineated by the critical substrate temperature for Mg re-evaporation and the Mg:O flux ratio. These regimes have impact on phase purity, quartz crystal microbalance calibration, and film microstructure. The universal decay in deposition rate above growth 10−5 Torr O2 is also considered. By introducing a third flux of inert argon gas, rate reduction is attributed to increased molecular scattering and not oxidation of the metal source.

The capabilities of various methods for fabricating silicon-based single-crystal structures are analyzed. The features and advantages of sublimation molecular-beam epitaxy are discussed.

Chemical beam epitaxy 성장법으로 InP/InGaAs 다층구조의 선택적 영역 에피성장 (selective area epitaxy)을 하였다.〈011〉방향에 평행한 직선패턴에서는 선폭이 작아지고,〈01-1〉방향에 평행한 직선패턴에서는 선폭이 증가하는 현상이 나타났는데 이는 InGaAs의〈311〉A와 B면이〈01-1〉방향에 평행한 직선패턴에서 성장되었기 때문으로 설명되었다. 성장속도가 1 ㎛/hr인 조건에서 5족 가스의 압력이 감소할수록 (100) 면 위에서 평평한 에피층이 성장되었는데 이는 5족 가스의 과포화현상에 의한 3족 원소의 표면이동으로 설명하였다.

The local vibration modes of N-H bonds Fourier transform infrared spectrometry for GaAsN films grown by chemical beam epitaxy are investigated. Four stretching modes of N-H bonds exist in the films. The absorption intensities of stretching modes at 3125, 3098 and 2952 cm-1 have no relationships, suggesting that at least three kinds of N-H related defects are formed in the GaAsN films. Major stretching modes are 3098 and 2952 cm-1. The integrated absorption (IA) of 3098 cm-1 is proportional to H concentration ([H]). The IA of 2952 cm-1 changes super linearly with [H]. A simple N-H bond and a complex defect including N-H are suggested as the origin of 3098 and 2952 cm-1, respectively.

The morphological and structural evolution is presented for GaN nanorods grown by chemical beam epitaxy on (0001) Al2O3 substrates. Their structural and optical properties are investigated by x-ray diffraction, scanning and transmission electron microscopy, and temperature-dependent photoluminescence measurements. While increasing the growth temperature and the flow rate of radio-frequency nitrogen radical, the three-dimensional growth mode will be enhanced to form one-dimensional nanostructures. The high density of well-aligned nanorods with a diameter of 30–50nm formed uniformly over the entire sapphire substrate. The x-ray diffraction patterns and transmission electron microscopic images indicate that the self-assembled GaN nanorods are a pure single crystal and preferentially oriented in the c-axis direction. Particularly, the “S-shape” behavior with localization of ∼10meV observed in the temperature-dependent photoluminescence might be ascribed to the fluctuation in crystallographic defects and compo...

The change in the surface concentration of N ([N] s ) on a GaAs surface under N and As source injections is investigated using the N atomic layer doping (N-ALD) technique, and the key factor determining [N] 5 is discussed. The As and N precursors source gases are trisdimethylaminoarsenic (TDMAAs, [N(CH 3 ) 2 ] 3 As) and monomethylhydrazine (MMHy, N 2 H 3 CH 3 ), respectively. N-ALD layers are prepared by using two gas injection sequences (A: MMHy injection and B: MMHy and TDMAAs injections). [N] s increases with decreasing growth temperature in both sequences. [N] 5 in sequence A is higher than that of sequence B. In sequence B, Δ[N] s /Δt is proportional to exp(-t/ τN ), where t and τ N are the gas injection time and the residence time of N, respectively. It is observed that the number of vacant sites, [V] s , N , remaining constant during gas injections. In sequence A, Δ[N] s /Δt cannot be fitted by a single exponential function, indicating that [V] S , N is not constant. From these results, we suggest that the vacant sites at the surface are created not only by N desorption but also by As desorption. It has been found that As desorption is enhanced by MMHy injection. As desorption reaction has been confirmed by in situ auger electron spectroscopy measurements. These results indicate that [N] s is determined by the competitive absorption between N and As, [V] S,N , and τ N· .

In this work, the growth of undoped InP nanowires on silicon(1 1 1) using gold as the metal seed particle was undertaken by chemical beam epitaxy. Prior to the growth process an ordered array of gold nano dots is integrated on the surface of a silicon substrate using self-assembled (hexagonal compact array) polystyrene nanospheres as the Au evaporation template. The size of the gold nanodots ranged from 20 to 150 nm. The InP nanowires were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL). The InP nanowires were found to grow tilted in the 〈1 0 0〉 direction and exhibited slightly broadened low-temperature photoluminescence emissions.

Hybrid reflections (HRs) involving substrate and layer planes (SL type) [Morelhao et al., Appl. Phys. Lett. 73 (15), 2194 (1998)] observed in Chemical Beam Epitaxy (CBE) grown InGaP/GaAs(001) structures were used as a three-dimensional probe to analyze structural properties of epitaxial layers. A set of (002) rocking curves (ω-scan) measured for each 15° in the azimuthal plane was arranged in a pole diagram in Φ for two samples with different layer thicknesses (#A - 58 nm and #B - 370 nm) and this allowed us to infer the azimuthal epilayer homogeneity in both samples. Also, it was shown the occurrence of (113) HR detected even in the thinner layer sample. Mappings of the HR diffraction condition (ω:Φ) allowed to observe the crystal truncation rod through the elongation of HR shape along the substrate secondary reflection streak which can indicate in-plane match of layer/ substrate lattice parameters.

A1. Surface processes A3. Chemical beam epitaxy A3. Metalorganic molecular beam epitaxy B1. Nitrides B2. Semiconducting indium compounds B2. Semiconducting ternary compounds abstract InGaN films with up to 19% indium composition are demonstrated for the first time by NH3-based MOMBE. Significant variations in alloy composition, growth rate, and III-alkyl desorption with substrate temperature, V/III, and Ga/In are reported. Desorbing III-alkyl species in the presence of TMIn are identified as predominantly III-methyl species resulting from mixed alkyl interactions at the growth interface. The results indicate that while reduced temperature growth is possible with NH3, growth is N-limited and control of active N, In/In-methyl surface coverage, and III-alkyl desorption set an upper limit to indium incorporation. Moreover, these three interdependent variables provide sensitive, exploitable mechanisms for intentional and controllable lateral composition inhomogeneity enabling novel three-dimensional device structures.

The electrical behavior of nitrogen–hydrogen (N–H) complexes and carbon (C) atoms in GaAsN films grown by the chemical beam epitaxy (CBE) method have been studied by comparing H concentrations and hole concentrations. The contributions of H and C concentrations ([H] and [C]) to ionized impurity scattering have been also investigated. In the GaAsN films, there were three acceptor levels (A0, A1, and A2). The energy levels of A1 and A2 were 130 and 55 meV, respectively. The concentration of the deepest acceptor (A0) was more than 1019 cm-3, which was higher than [H] and [C]. A2 was observed only in films with a high [C]. The amount of A1 was proportional to [H]. Most of the residual H formed N–H complexes; thus, it is concluded that the N–H complex behaved as an acceptor in GaAsN films. At low temperatures, ionized impurity scattering limited the total hole mobility. The inverse numbers of the coefficients for the ionized scattering were consistent with [C] instead of [H]. This suggests that all the residual C atoms were ionized owing to compensation by the donors. A disagreement between N composition and alloy scattering has been also detected. This might indicate a fluctuation in the N composition in the GaAsN films.

The flow-rate-modulated chemical beam epitaxy (FM-CBE) method was developed and implemented on the basis of the discussion of the desorption velocities of absorbed species originating from N source gas [MMHy, (CH3)N2H3] for decreasing the residual carbon (C) concentration in GaAsN films. In this method, the Ga source [TEGa, Ga(C2H5)3] was supplied intermittently, while the As [TDMAAs, As(N(CH3)2)3] and N sources (MMHy) were supplied continuously. Below growth temperatures of 440 °C, the residual C concentrations in GaAsN films was reduced to 1/10 that in conventional CBE films, with no change in N concentration. However, above 440 °C, N concentration decreased drastically with FM-CBE. It was concluded that the reduction in C concentration by FM-CBE was attributed to the decrease in –NHCH3 coverage on the growing surface by –NH2 substitution during the intermittence of the TEGa flow. FM-CBE was an effective method for decreasing residual C concentration while maintaining the N concentration in GaAsN films below 440 °C.

The amount of residual H in the GaAsN film grown by chemical beam epitaxy (CBE) can be decreased by flow rate modulation growth. Many H atoms in the films grown by CBE exist as N–H or N–H 2 structures. Although a higher growth temperature was required for decreasing the H concentration ([H]), it caused a decrease in the N concentration ([N]). A reduction in [H] while keeping [N] constant was necessary. By providing an intermittent supply of Ga source while continuously supplying As and N sources, [H] effectively decreased in comparison with the [H] value in the film grown at the same temperature by conventional CBE without reducing [N].

The tremendous interest in nanoscale structures such as quantum dots (zero-dimension) and wires (quasi-one-dimension) stems from their size-dependent properties. One-dimensional (1D) semiconductor nanostructures are of particular interest because of their potential applications in nanoscale electronic and optoelectronic devices. For 1D semiconductor nanomaterials to have wide practical application, however, several areas require further development. In particular, the fabrication of desired 1D nanomaterials with tailored atomic structures and their assembly into functional devices are still major challenges for nanotechnologists. In this review, we focus on the status of research on the formation of nanowire structures via highly anisotropic growth of nanocrystals of semiconductor and metal oxide materials with an emphasis on the structural characterization of the nucleation, initial growth, defects and interface structures, as well as on theoretical analyses of nanocrystal formation, reactivity and stability. We review various methods used and mechanisms involved to generate 1D nanostructures from different material systems through self-organized growth techniques including vapor–liquid–solid growth, oxide-assisted chemical vapor deposition (without a metal catalyst), laser ablation, thermal evaporation, metal-catalyzed molecular beam epitaxy, chemical beam epitaxy and hydrothermal reaction. 1D nanostructures grown by these technologies have been observed to exhibit unusual growth phenomena and unexpected properties, e.g., diameter-dependent and temperature-dependent growth directions, structural transformation by enhanced photothermal effects and phase transformation induced by the point contact reaction in ultra-thin semiconductor nanowires. Recent progress in controlling growth directions, defects, interface structures, structural transformation, contacts and hetero-junctions in 1D nanostructures is addressed. Also reviewed are the quantitative explorations and predictions of some challenging 1D nanostructures and descriptions of the growth mechanisms of 1D nanostructures, based on the energetic, dynamic and kinetic behaviors of the building block nanostructures and their surfaces and/or interfaces.

The selective growth of InP/InGaAs ridges aligned along the 〈0 1 0〉 direction was studied using scanning electron microscopy and photoluminescence measurements. The ridges exhibit very smooth {1 1 0} sidewalls and (0 0 1) top facets. The diffusion of the group III species from the sidewalls to the top (0 0 1) surface was modelled to provide a predictive tool for determining ridge growth, and the optical properties of InGaAs QWs incorporated in the ridges. No growth occurs on the {1 1 0} sidewalls until the ridges complete due to the diffusion of In species to the top (0 0 1) facet. The situation for Ga is quite different, with no diffusion off the {1 1 0} facets observed, and little or no Ga being incorporated on the {1 1 0} surface before or after ridge completion.

As a result of developing wide bandgap InGaP double hetero structure tunnel junction for sub-cell interconnection, InGaAs middle cell lattice-matched to Ge substrate, and InGaP-Ge heteroface structure bottom cell, we have demonstrated 38.9% efficiency at 489-suns AM1.5 with InGaP/InGaP/Ge 3-junction solar cells by in-house measurements. In addition, as a result of developing a non-imaging Fresnel lens as primary optics, a glass-rod kaleidoscope homogenizer as secondary optics and heat conductive concentrator solar cell modules, we have demonstrated 28.9% efficiency with 550-suns concentrator cell modules with an area of 5445 cm2. In order to realize 40% and 50% efficiency, new approaches for novel materials and structures are being studied. We have obtained the following results: (1) improvements of lattice-mismatched InGaP/InGaAs/Ge 3-junction solar cell property as a result of dislocation density reduction by using thermal cycle annealing, (2) high quality (In)GaAsN material for 4- and 5-junction applications by chemical beam epitaxy, (3) 11.27% efficiency InGaAsN single-junction cells, (4) 18.27% efficiency InGaAs/GaAs potentially modulated quantum well cells, and (5) 7.65% efficiency InAs quantum dot cells.

The local vibrational modes (LVMs) observed by Fourier transform infrared (FTIR) spectroscopy in GaAsN films grown by chemical beam epitaxy (CBE) was studied, and the influence of the nitrogen–hydrogen bond (N–H) concentration on the hole concentration was investigated. The absorption peak around 936 cm−1 is suggested to be the second harmonic mode of the substitutional N, NAs, LVM around 469 cm−1. The absorption peak around 960 cm−1 is suggested to be the wagging mode of the N–H, where the stretch mode is observed around 3098 cm−1. The hole concentration linearly increases with increasing N–H concentration, and the slope increases with increasing growth temperature. It indicates that the hole concentration in GaAsN film is determined by both the number of the N–H and unknown defect, such as impurities, vacancies, and interstitials. This defect concentration increases with increasing growth temperature, suggesting that it is determined by Arrhenius type reaction.

This work presents the selective growth of three-dimensional metallic gallium nitride structures on silicon substrates by chemical beam epitaxy (CBE) with a subsequent plasma nitridation process. The use of titanium pre-deposited stripes over silicon (1 0 0) is shown to provide high selectivity where spherical and semi-spherical structures are obtained only over the metal. These structures have diameters ranging from 100 nm to 3 μm depending on the growth conditions. The nitridation process was performed on an electron cyclotron resonance (ECR) plasma system. Raman micro-spectroscopy results showed GaN formation with zinc blend crystal structure and photoluminescence emission in the visible spectrum in a range between 350 and 650 nm.

Quantitative structural information about epitaxial arrays of nanowires are reported for a InAs/InP longitudinal heterostructure grown by chemical beam epitaxy on an InAs (111)B substrate. Grazing incidence X-ray diffraction allows the separation of the nanowire contribution from the substrate overgrowth and gives averaged information about crystallographic phases, epitaxial relationships (with orientation distribution), and strain. In-plane strain inhomogeneities, intrinsic to the nanowires geometry, are measured and compared to atomistic simulations. Small-angle X-ray scattering evidences the hexagonal symmetry of the nanowire cross-section and provides a rough estimate of size fluctuations.

GaAsN thin films were grown by chemical beam epitaxy (CBE) with monomethylhydrazine (MMHy) as a N source. Processes that determine the N composition in the GaAsN thin films were investigated in the growth temperature range from 340 to 480 °C. When growth temperature is low (340–390 °C), N composition is mainly determined by the supply of N species generated from MMHy and growth rate, since the desorption rate of N species from the growing surface is low. The effect of the desorption of N species on N composition is enhanced by increasing growth temperature (390–445 °C). When growth temperature is high (445–480 °C), the degree of N atom segregation from the grown layer increases, resulting in a marked decrease in N composition. Thus, N composition is determined by the balance of supply and desorption of N species, and growth rate.

The intensity of the flux of activated nitrogen from an RF inductively coupled discharge source for the plasma-assisted molecular beam epitaxy (PAMBE) of group III nitrides (A3N) can be linearly controlled using a modified output diaphragm design and increased nitrogen supply (∼5 sccm). This source provides a linear variation of the maximum A3N growth rate from 0.2 to 0.8 μm/h for the RF power controlled between 110 and 200 W, respectively. The use of excited nitrogen molecules favorably influences the growth of GaN and InN epilayers, which are characterized by a perfect structure and high optical quality.

The growth and characteristics of ultrahigh carbon-doped p-type InGaAs lattice matched to InP by gas source molecular beam epitaxy (GSMBE) using carbon tetrabromide (CBr 4 ) as a doping source was investigated. The effects of growth temperature, group V supply pressure and CBr 4 supply pressure on the composition, hole mobility and concentration of carbon-doped InGaAs were studied. The dependence of hydrogen passivation effect on different AsH 3 supply pressure and different growth temperature were researched. Ultrahigh net hole concentration and room-temperature mobility of 1×10 20 cm −3 and 45 cm 2 /V s, respectively, were achieved without any postgrowth annealing. Mobility of the ultrahigh carbon-doped InGaAs using CBr 4 compared favorably to those of CBE grown carbon-doped InGaAs using CBr 4 and molecular beam epitaxy grown beryllium (Be)-doped InGaAs grown at low temperature. The highly carbon-doped InGaAs layers grown by GSMBE using CBr 4 as a doping source were used for the growth of high performance, highly carbon-doped base InP/InGaAs heterojunction bipolar transistor epitaxial layer structures.

Photovoltaic properties of a preliminary set of 1-1.2 eV dilute nitride GaAsN/GaAs MQW solar cells grown by chemical beam epitaxy are investigated. The study reveals, as expected from the enhancement of effective masses, unusually high photo-conversion strength of the MQW region that exceeds by nearly two-fold those reported for conventional MQW solar cells of comparable bandgaps. Despite a current output (∼25 A m -2 in absence of ARC) comparable to that of conventional GaInNAs solar cells, output voltages (e.g. ∼0.6 V for a 1.1 eV MQW cell) appear to be significantly higher than those reported for bulk-like counterparts. Bias-dependent external quantum efficiency measurements reveal an incomplete collection of photo-generated carriers from the wells under operating conditions (forward bias), which should be mitigated by the use of thinner barrier.

Crystal quality of GaAsN films can be improved by using CBE for low-temperature growth. However, low-temperature growth increases C incorporation in the films, which degrades their electrical properties. Consequently, C incorporation was investigated in view of the surface reaction of N sources on a substrate surface, and MMHy and DMHy were compared. When MMHy was used as an N source, C concentration in GaAsN drastically increases below 380 °C than that in GaAs due to insufficient CHx desorption. In the case of DMHy, N(CH3)2 is desorbed more readily than CHx, therefore, the C concentration can then be reduced using DMHy.

In this work we investigate the evolution of the growth mode and the dependence of the structural and optical properties of III–V dilute nitrides with the growth temperature and the presence of hydrogen. GaAsN epilayers were fabricated on (0 0 1) GaAs substrates by rf nitrogen plasma-assisted chemical beam epitaxy. Various amounts of hydrogen were introduced independently in the growth chamber during the GaAsN epilayer fabrication. Reflection high-energy electron diffraction (RHEED) was used to monitor the evolution of the surface reconstruction during growth, while the interaction of the residual hydrogen with the rf plasma source was monitored, simultaneously and in real time, using optical spectroscopy. The presence of hydrogen and slight variations of the growth temperature resulted in noticeable changes in the surface reconstruction during the initial stages of GaAsN fabrication. For sufficiently high amounts of hydrogen, the RHEED image at the onset of GaAsN growth was characterized by the appearance of three-dimensional features, indicating an increased surface disorder; however, after the subsequent growth of few monolayers, two-dimensional RHEED was recovered for all samples regardless of the amount of residual hydrogen. In addition, samples fabricated under excess hydrogen exhibited an apparent nitrogen content reduction, as indicated by high-resolution X-ray diffraction analysis, and a noteworthy blue shift and signal degradation of their low-temperature photoluminescence spectra compared to samples that were fabricated under lower hydrogen partial pressures.

We present a simple route for ZnSe nanowire growth in the ablation crater on a ZnSe crystal surface. The crystal wafer, which was horizontally dipped in pure water, was irradiated by femtosecond laser pulses. No furnace, vacuum chamber or any metal catalyst were used in this experiment. The size of the nanowires is about 1–3 μm long and 50–150 nm in diameter. The growth rate is 1–3 μm/s, which is much higher than that achieved with molecular-beam epitaxy and chemical vapor deposition methods. Our discovery reveals a rapid and simple way to grow nanowires on designed micro-patterns, which may have potential applications in microscopic optoelectronics.

Growth of ZnO films was carried out on the c -plane sapphire ( α -Al 2 O 3 (0 0 0 1)) and glass substrates by metalorganic molecular beam epitaxy (MOMBE) using diethylzinc (DEZn) and H 2 O as source precursors. The lattice constant c of the ZnO/α-Al 2 O 3 (0 0 0 1) layer decreased with increasing feeding ratio of H 2 O to DEZn (VI/II ratio). Photouminescence (PL) intensity ratio of the green band to the near-band-edge (NBE) emission ( I GB / I NBE ) became smaller with increasing VI/II ratio. These results are probably due to the decrease in oxygen vacancy concentration. Highly c -axis-oriented polycrystalline ZnO films were grown at T S ⩾300 °C under VI/II=25. The full-width at half-maximum (FWHM) value of the (0 0 2) diffraction peak was minimum at T S =300–375 °C. The I GB / I NBE ratio for the polycrystalline ZnO/glass film showed minimum value at T S =300 °C. The quality of the ZnO/glass film was best at T S =300–375 °C, which is lower in comparison with the ZnO/α-Al 2 O 3 (0 0 0 1) layer.

We investigate a growth mechanism which allows for the fabrication of catalyst-free InAs nanowires on Si (111) substrates by chemical beam epitaxy. Our growth protocol consists of successive low-temperature (LT) nucleation and high-temperature growth steps. This method produces non-tapered InAs nanowires with controllable length and diameter. We show that InAs nanowires evolve from the islands formed during the LT nucleation step and grow truly catalyst-free, without any indium droplets at the tip. The impact of different growth parameters on the nanowire morphology is presented. In particular, good control over nanowire aspect ratio is demonstrated. A better understanding of the growth process is obtained through the development of a theoretical model combining the diffusion-induced growth scenario with some specific features of the catalyst-free growth mechanism, along with the analysis of the V/III flow ratio influencing material incorporation. As a result, we perform a full mapping of the nanowire morphology versus growth parameters which provides useful general guidelines on the self-induced formation of III-V nanowires on silicon.

In this work, we demonstrate a silver catalyzed heteroepitaxial growth of gallium phosphide nanowires (GaP NWs) on silicon. The morphology and growth direction of GaP NWs on differently orientated Si substrates were investigated. From crystallographic analysis, we inferred that Ag from catalyst is incorporated into the GaP during the chemical beam epitaxy (CBE) process. Using the PL spectrum and time-resolved emission spectroscopy, the optical properties of Ag-catalyzed GaP NWs were greatly modified, with bandgap transitions in the blue range. The Raman characterizations further confirmed the Ag incorporation into GaP during the growth. From the bandgap calculations, it was deduced that Ag was substituted on the Ga site with bandgap broadening. The in situ Ag-alloying during the growth of Ag-catalyzed GaP NWs greatly modified the band structure of GaP, and could lead to further applications in optoelectronics for low-dimensional GaP-based nanomaterials.