Indium Desorption Research Articles

Desorption kinetics of indium adlayers on GaN(0001): Fractional order and non-monotonic behavior

Epitaxial growth is a dynamic process and, to the first order, is governed by the nature and the rates of elementary surface kinetic mechanisms, such as adatom desorption. In compound-type growing surfaces, particularly in III-nitride molecular beam epitaxy, where the presence of a metallic surface bilayer has a catalytic role, desorption also affects the rates of other elementary mechanisms. In this study, we investigated the desorption of an indium (In) adlayer from GaN(0001) surfaces, a critical kinetic process in the epitaxy of In-containing alloys, using reflection high-energy electron diffraction, density functional theory calculations, and quasi-continuous modeling methods to reveal the underlying physical mechanisms. Our results demonstrate that while the indium bilayer desorbs in a layer-by-layer mode, the desorption mechanisms from the bottom and top monolayers differ significantly. The bottom follows a 3/4 order Polanyi–Wigner relation, attributed to contributions from two different adlayer phases. The top monolayer desorption exhibits a non-monotonic dependence on coverage. This is associated with the liquidus status of this monolayer and its continuous restructuring during desorption. These findings clarify and quantify indium desorption processes from GaN(0001) surfaces, offering insights into analogous mechanisms in other compound-type material systems.

Molecular Beam Epitaxy Growth of GaN/InGaN Heterostructures under In‐Bilayer Stabilized Conditions

Molecular beam epitaxy is applied for the GaN/InGaN growth under In‐bilayer stabilized conditions, which require substrate temperatures above 580 °C for sufficient indium desorption. Under these conditions the indium content is limited to , as determined by a novel reflection high energy electron diffraction technique, which is based on indium adsorption and subsequent consumption at varying gallium flux. As‐grown structures show degraded surfaces after indium desorption. This effect is eliminated by applying excess gallium before and after InGaN growth, which results in morphologies and dislocation densities comparable to GaN/AlGaN structures.

Startified thermal degradation in blue InGaN quantum well structures: P-GaN growth temperature and its influence on quantum well optical properties

Thermal degradation in blue InGaN multi-quantum well (MQW) structures induced by varying high p-GaN growth temperature and the subsequent influence on the optical properties of MQW are investigated. The results indicate that higher p-GaN growth temperatures improve p-GaN layer contact quality, but may lead to an optical property degradation of InGaN MQWs. A stratified thermal degradation mechanism is observed. The degradation primarily affects the upper quantum barrier layers and results in indium desorption and re-evaporation, where elevated p-GaN growth temperatures may induce more indium segregation and decomposition than in lower layers of MQW. In extreme conditions, such as 1060℃, indium atoms in lower layers escape, causing partial lattice structure corruption and severe degradation in MQW structure, which is also more distinctive in the upper layers.

Highly Si‐Doped GaN Regrown by Metal–Organic Vapor‐Phase Epitaxy for Ohmic Contact Applied to Quaternary Barrier‐Based High‐Electron‐Mobility Transistors

The quaternary barrier InAlGaN is suitable for GaN high‐electron‐mobility transistors (HEMT) power microwave applications. High doping of the semiconductor under the drain and source is a known suitable solution to achieve low ohmic contact resistance. However, InAlGaN quaternary alloys require a low thermal budget to avoid indium desorption from the active layer during regrowth and thus deteriorating the barrier. Herein, a selective‐area growth technique at 850 °C by metal–organic vapor‐phase epitaxy (MOVPE) to achieve low contact resistance with respect to temperature constraint is presented. Regrowth temperature and mask geometry are investigated to achieve selectivity and control of the regrowth rate. The use of H2 as carrier gas decomposes the GaN buffer layer and damages the surface, creating material cluster during regrowth. Growth with N2 carrier gas shows nonselective epitaxy, as there are deposits on the entire surface of the dielectric mask. Switching from one carrier gas to another depending on the step in the MOVPE reactor helps to control both the morphology and selectivity. The resulting high doping levels of 8 × 1019 cm−3 lead to a low contact resistance of 0.26 Ω mm.

In-Situ Tailoring of Vertically Coupled InAs p-i-p Quantum-Dot Infrared Photodetectors: Toward Homogeneous Dot Size Distribution and Minimization of In–Ga Intermixing

The authors report a detailed analysis of an epitaxial growth technique for indium arsenide (InAs) Quantum-dot infrared photodetectors circumvent the detrimental effects arising from the progressively increasing dot-size in vertically coupled heterostructures. Constant overgrowth percentage of the vertically coupled dot-layers has been achieved with the implementation of the growth strategy, which has been validated by cross-sectional transmission electron microscopy (X-TEM) images of the samples. The optical characteristics of these samples have been analyzed through photoluminescence spectroscopy and photoluminescence excitation spectroscopy (PL and PLE) measurements which show longer wavelength response and reduced full width at half-maxima (fwhm) upon implementation of the growth strategy. X-TEM and in-plane and out-of-plane high resolution X-ray diffraction (HR-XRD) measurements suggest morphological improvement upon implementation of the growth strategy, with a reduction in the indium desorption and lowering of defects and dislocation densities. Excellent correlation has been found between the different experimental results and also their theoretical simulations. The fabricated single-pixel photodetectors at low temperature (T = 14 K) show a broad response extending up to the MWIR region (∼4.5 μm) for one of the samples. Also, a strong spectral response in the SWIR region is obtained even at room temperature (T = 300 K). The highest responsivity (Rp) and specific detectivity (D*) values obtained are 166.17 A/W and 8.39 × 1010 cm Hz1/2 W–1 at a bias of 5 V and 300 K temperature.

Observation and mitigation of RF-plasma-induced damage to III-nitrides grown by molecular beam epitaxy

In this work, radio-frequency (RF) plasma-induced damage to III-nitride surfaces and bulk defects is observed and mitigated. It is shown that for InN films, the surface is more sensitive to plasma-induced damage than GaN films, as observed via atomic force microscopy and reflection high energy electron diffraction. In order to isolate any possible plasma-induced damage, a growth window for InN is established, and temperature ranges are determined for other damaging effects which include roughening due to low adatom mobility, InN decomposition, and indium desorption. In situ plasma monitoring and optimization are accomplished with a combination of optical emission spectroscopy as well as a remote Langmuir probe. It is shown that by increasing the plasma nitrogen flow, the positive ion content increases; however, the ion acceleration potential reduces. Additionally, a reduced RF plasma power results in a reduction of atomic nitrogen species. These plasma species and energetic variations result in variations in the bulk unintentional background electron concentrations observed by room temperature Hall effect measurements of ∼1 μm thick InN films. By increasing the nitrogen flow from 2.5 to 7.5 sccm for a constant RF power of 350 W, the background electron concentration decreases by 74% from 1.36 × 1019 cm−3 to 3.54 × 1018 cm−3, while maintaining a smooth surface morphology. Additionally, photoluminescence spectra indicate optical emission energies shift from ∼0.81 to 0.71 eV (closer to the fundamental bandgap of InN) by limiting the damaging plasma species. Finally, conditions are presented to further minimize plasma-induced damage in III-nitride devices.

In situ lift-off of InAs quantum dots by pulsed laser irradiation

InAs/GaAs quantum dots (QDs) grown by molecular beam epitaxy were subjected to in situ irradiation using a mono-beam pulsed laser. The evolution of the QD morphology was investigated as a function of irradiation intensity at temperatures of 525 °C and 480 °C. The temperature was found to exert a considerable influence on the reaction of the QDs to the irradiation. At the higher temperature (525 °C), both the height and width of the InAs QDs gradually decreased with increasing irradiation intensity, which was ascribed to the dominant effect of the laser desorption of indium. In contrast, at the lower temperature (480 °C), the height of the InAs islands decreased with increasing irradiation intensity while the width exhibited unexpected broadening, which was attributed to a combination of laser desorption and laser diffusion of indium. Remarkably, at the higher temperature, laser irradiation above a certain threshold intensity resulted in the lift off of the InAs QDs to afford a clear, smooth, and perfect GaAs surface. Through subsequent growth of QDs on this surface, it was found that the QDs exhibited the same nucleation properties and optical quality as the common Stranski–Krastanov mode on an as-prepared GaAs surface. Therefore, we have developed a technology for the damage-resistant fabrication of QDs using in situ pulsed laser irradiation (LIR), which is expected to find potential applications in the manufacture of patterned QDs upon upgrading the mono-beam irradiation to multi-beam interference irradiation in the future.

Impact of an InxGa1–xAs Capping Layer in Impeding Indium Desorption from Vertically Coupled InAs/GaAs Quantum Dot Interfaces

This study describes the effect of a thin GaAs spacer of 4.5 nm thickness in a bilayer-coupled InAs quantum dot (QD) heterostructure. Here, we report the first demonstration of InAs/GaAs QDs capped by self-assembled InxGa1–xAs layers. Self-assembled InxGa1–xAs layers were introduced into each intermediate layer across the interface of InAs QDs and the GaAs layer in a vertical-coupled bilayer QD (VCBQD) heterostructure to prevent indium desorption from the QDs. A change in the indium content in the seed-layer InAs QDs changes the self-assembly position and modifies the InxGa1–xAs layer thickness. A theoretical approach was presented to study the formation of self-assembled InxGa1–xAs layers at each strain-free layer. We showed that the strain energy at the second intermediate (εzz2) layer is greater than that at the first intermediate (εzz1) layer; εzz2 depends on the vertical strain channel length. The impact of the InxGa1–xAs layer thickness on the strain energy was studied using high-resolution transmission electron microscopy; a shorter strain channel length was found to facilitate the formation of a more relaxed and larger-sized self-assembled InxGa1–xAs layer in the active layer. This InxGa1–xAs layer formed at the intermediate layer acts as a capping layer or a protective shield for the indium adatoms, preventing their desorption from the InAs QDs. Furthermore, we studied the thermal stability of the self-assembled InxGa1–xAs layer by annealing the VCBQD samples at 700 and 800 °C. This aspect has been investigated for the first time ever in a study of the coupling efficiency between the InAs QDs and InxGa1–xAs capping layer. A high-resolution in-plane (2θχ/ϕ) reciprocal space mapping (RSM) technique provided the connection between the in-plane reciprocal lattice point of the InAs QDs and InxGa1–xAs layers and revealed the strain and coupling between them. InAs QDs fully covered with the self-assembled InxGa1–xAs layer enhanced the photoluminescence intensity by 77% and had an activation energy of 467 meV.

Effects of in-situ surface modification by pulsed laser on InAs/GaAs (001) quantum dot growth

InAs/GaAs quantum dots (QDs) have been extensively applied to high-performance optoelectronic devices due to their unique physical properties. In order to exploit the potential advantages of these QD-devices, it is necessary to control the QDs in density, uniformity and nucleation sites. In this work, a novel research of in-situ pulsed laser modifying InAs wetting layer is carried out to explore a new controllable method of growing InAs/GaAs(001) QDs based on a specially designed molecular beam epitaxy (MBE) system equipped with laser viewports. Firstly, a 300 nm GaAs buffer layer is grown on GaAs (001) substrate at 580 ℃ and the temperature decreases to 480 ℃ to deposit InAs. As soon as the amount of InAs deposition reaches 0.9 ML, a single laser pulse ( =355 nm, pulse duration ～ 10 ns) with an energy intensity of ～ 40.5 mJ/cm2 is in-situ introduced to irradiate the surface. Then, the sample is taken out and then its surface modification is immediately evaluated by atomic force microscope measurement. Atomic layer removal nano-holes elongated in the direction, and a surface density of ～2.0109 cm-2 are observed on the wetting layer. We attribute the morphology change to being due to laser-induced atom desorption. Because indium atoms should be easily desorbed away at substrate temperature of 480 ℃ during the laser irradiation, some vacancy defects are created. Then atoms adjacent to those defects would become weakly bounded, resulting in preferential desorption around the defect sites in sequence. Therefore, atomic layer removal is intensified by such a kind of chain effect and finally nano-holes are developed on the surface. In order to make clear how these nano holes of special kind influence the InAs/GaAs (001) QD growth, we perform another study by continuously depositing the InAs after the irradiation at the same thickness of 0.9 ML. It is found that when 1.7 ML InAs is deposited, QDs start to nucleate into some nano-holes and then are further deposited with an InAs coverage of 1.9 MLs, all the nano holes would be completely nucleated by QDs with a good uniformity, and there are no QDs in the remaining area. Such an effect of QD preferential nucleation in nano-holes could be explained by the following two causes. Firstly, adsorbed indium atoms tend to immigrate into nano-holes for lower surface energy induced by the concave surface curvature. The enhanced accumulation of Indium is in favor of the preferential nucleation of QDs in nano-holes. On the other hand, QD growth in areas outside the nano holes is depressed for indium desorption in pulsed laser irradiation process. In conclusion, our studies of in-situ laser-induced surface modification reported here provide a potential solution of controllable InAs/GaAs (001) QD growth.

Indium incorporation dynamics in N-polar InAlN thin films grown by plasma-assisted molecular beam epitaxy on freestanding GaN substrates

N-polar InAlN thin films were grown by plasma-assisted molecular beam epitaxy on freestanding GaN substrates under N-rich conditions. Indium and aluminum fluxes were varied independently at substrate temperatures below and above the onset of thermal desorption of indium. At low temperatures, the InAlN composition and growth rate are determined by the group-III fluxes. With increasing substrate temperature, the surface morphology transitions from quasi-3D to a smooth, 2D morphology at temperatures significantly above the onset of indium loss. At higher temperatures, we observe increased indium evaporation with higher indium fluxes and a suppression of indium evaporation with increased aluminum flux. The final optimized InAlN thin film results in step-flow morphology with rms roughness of 0.19nm and high interfacial quality.

Abnormal InGaN growth behavior in indium-desorption regime in metalorganic chemical vapor deposition

InGaN strained bulk layers were grown by low-pressure metalorganic chemical vapor deposition on c-plane GaN/sapphire templates. Two growth regimes, mass-transport limited regime and indium desorption regime, were examined for InGaN growth. In the indium desorption regime, more indium source must be fed to keep a constant indium content. In the indium desorption regime, we found an abnormally enhanced GaN growth rate, which was proved to be related to the indium desorption and dependent on the growth temperature and the indium source flow. Due to the enhanced growth rate, the optical quality of In0.16Ga0.84N layers degraded significantly.

GaN tubes with coaxial non‐ and semipolar GaInN quantum wells

AbstractWe present the position‐controlled growth of GaN nanotubes with coaxial GaInN quantum wells by using ZnO nanowires grown on top of GaN pyramids as templates. High resolution scanning transmission electron microscopy allows us to perform a detailed structural analysis of individual tubes. In particular, we report about structural properties like indium incorporation, thickness, and homogeneity of quantum wells realized on nonpolar m‐plane side facets or on semipolar tips. Additionally, high resolution spatially and spectrally resolved cathodoluminescence spectroscopy performed at low temperature enables us to clearly identify the quantum well luminescence contributions for different kinds of facets on a single tube. The luminescence of the quantum wells deposited at variable temperatures shows a clear spectral shift in the cathodoluminescence signal, yielding an activation energy for the indium desorption from the m‐plane side facets of about 1.6 eV. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effects of annealing on the structural properties of indium rich InGaN films

Indium rich (In-rich) InGaN films were grown on Ge (111) substrate by plasma assisted molecular beam epitaxy with thin GaN as a buffer layer. The effects of annealing temperature and annealing time on the structural properties of In-rich InGaN films were investigated by X-ray diffraction (XRD). XRD results indicate that the as-grown InGaN films annealed at different temperatures for 1 min and 1 h respectively did not improve the film crystalline quality. But with the annealing at 750 °C and 800 °C for 1 min respectively the metallic indium was desorbed from the InGaN structure. The InGaN films annealed at higher than 660 °C for 1 h also showed the indium desorption. The InGaN film has the best film quality after annealed at 660 °C for 6 h with the full-width at half-maximum of InGaN (002) peak to be 879 arcsec. The InGaN crystalline quality started to degrade after annealed at the temperatures higher than 660 °C for 6 h.

Theoretical study of the indium incorporation into III-V compounds revisited: The role of indium segregation and desorption

Indium based III-V compounds are very important technological materials. However, the indium incorporation depends on several phenomena, among them, the influence of indium segregation has been the most studied. In this paper, we show that to predict accurately the energy levels of In based III-V quantum structures, besides the indium segregation, the indium desorption must also be considered. In order to verify this assumption, we consider InGaAs/GaAs quantum wells as a benchmark case, and simulate 48 different quantum wells comparing with photoluminescence results.

Wetting layer evolution and its temperature dependence during self-assembly of InAs/GaAs quantum dots

For InAs/GaAs(001) quantum dot (QD) system, the wetting layer (WL) evolution and its temperature dependence were studied using reflectance difference spectroscopy and were analyzed with a rate equation model. WL thicknesses showed a monotonic increase at relatively low growth temperatures but showed an initial increase and then decrease at higher temperatures, which were unexpected from a thermodynamic understanding. By adopting a rate equation model, the temperature dependence of QD formation rate was assigned as the origin of different WL evolutions. A brief discussion on the indium desorption was given. Those results gave hints of the kinetic aspects of QD self-assembly.

Temperature dependent photoluminescence investigation of the effect of growth pause induced ripening in InAs/GaAs quantum dot heterostructures

Self-assembled InAs/GaAs quantum dot (QD) heterostructures grown by solid state molecular beam epitaxy (MBE) were subjected to growth ripening pause of comparatively shorter durations (0–50s) at the growth temperature (520°C). The islands are found to increase in size with the growth pause and correspondingly their density decreases. Though the photoluminescence spectra of the islands subjected to growth pause is found to follow conventional QD systems, a contradiction is noticed in the calculated values of the activation energy of the dots. We ascribed this contradiction due to the poor crystalline quality of the ripened QDs as a result of desorption and sublimation of indium during the pause at high growth temperature.

Evaluation of the In desorption during the capping process of diluted nitride In(Ga)As quantum dots

Diluted nitride self-assembled In(Ga)AsN quantum dots (QDs) grown on GaAs substrates are potential candidates to emit in the windows of maximum transmittance for optical fibres (1.3-1.55 μm). In this paper, we analyse the effect of nitrogen addition on the indium desorption occurring during the capping process of InxGa1−xAs QDs (x = l and 0.7). The samples have been grown by molecular beam epitaxy and studied through transmission electron microscopy (TEM) and photoluminescence techniques. The composition distribution inside the dots was determined by statistical moiré analysis and measured by energy dispersive X-ray spectroscopy. First, the addition of nitrogen in In(Ga)As QDs gave rise to a strong redshift in the emission peak, together with a large loss of intensity and monochromaticity. Moreover, these samples showed changes in the QDs morphology as well as an increase in the density of defects. The statistical compositional analysis displayed a normal distribution in InAs QDs with an average In content of 0.7. Nevertheless, the addition of Ga and/or N leads to a bimodal distribution of the Indium content with two separated QD populations. We suggest that the nitrogen incorporation enhances the indium fixation inside the QDs where the indium/gallium ratio plays an important role in this process. The strong redshift observed in the PL should be explained not only by the N incorporation but also by the higher In content inside the QDs.

Improved luminescence and thermal stability of semipolar (11-22) InGaN quantum dots

Semipolar (11-22)-oriented InGaN/GaN quantum dots (QDs) emitting in the 380–620 nm spectral range were synthesized by plasma-assisted molecular-beam epitaxy. The influence of the growth temperature on the properties of InGaN QDs has been investigated by photoluminescence and transmission electron microscopy. Growth temperatures low enough to prevent indium desorption provide a favorable environment to semipolar plane (11-22) to enhance the internal quantum efficiency of InGaN/GaN nanostructures.

Improvement of structural and luminescence properties in InGaN/GaN multiple quantum wells by symmetrical thin low temperature-GaN layers

InGaN/GaN quantum wells (QWs) with symmetrical ultra thin (about 0.5nm) low temperature GaN (LT-GaN) layers bounding each InGaN layer were grown by metal-organic vapor phase epitaxy (MOVPE). From the high resolution X-ray diffraction (HR-XRD) measurement, it showed improved well-barrier interface abruptness compared to the reference MQWs without the LT-GaN layers. In addition, the V-defect density and surface roughness were reduced, especially with the depth of V-defect as low as 0.7nm. Based on the temperature dependence photoluminescence (TDPL) experiments, the internal quantum efficiency (IQE) was increased from 21.2% to 30.1% by inserting the LT-GaN layers. The carrier lifetime obtained from room temperature time resolved photoluminescence (TRPL) measurement was 7.95ns, which was longer than 5.34ns for reference MQWs. These results indicated that these additional symmetrical thin LT-GaN layers enhanced the mobility of indium and gallium atoms as well as suppressed the indium desorption for growth high quality InGaN layers and in turn improved its structural and luminescence properties.

Retardation of Liquid Indium Flow in Indium Oxide Nanotubes

High-resolution transmission electron microscopy and energy-dispersive X-ray analysis carried out on indium oxide nanotubes grown by a chemical vapor deposition technique show the presence of indium metal segments along the indium oxide (IO) nanotube axis having one end closed. A real-time HRTEM video in continuous mode imaging has been carried out to study the directional flow of liquid indium. Electron-beam-induced heating results in the increase in indium vapor pressure and desorption of gases at the closed end of the IO nanotubes. This buildup of differential pressure between open and closed columns leads to the flow of indium away from the closed end of the IO nanotube. Interestingly, the indium flow rate was observed to decrease from 2.8 to 0.3 nm/s with a corresponding decrease in the nanotubes’ diameter from 138 to 38 nm. This study indicates that the wetting properties of the liquid−host nanotube interface critically decides the fluid dynamics at nanoscale, and depending upon the interfacial prop...