Indium Diffusion Research Articles

Fast Diffusion and Segregation along Threading Dislocations in Semiconductor Heterostructures

Heterogeneous integration of semiconductors combines the functionality of different materials,enabling technologies such as III-V lasers and solar cells on silicon and GaN LEDs on sapphire. However, threading dislocations generated during theepitaxy of these dissimilar materialsremain a key obstacle to the success of this approach due to reduced device efficiencies and reliability. Strategies to alleviate this and understand charge carrier recombination at threading dislocations now needan accurate description of the structure of threading dislocationsin semiconductor heterostructures. We show that the composition around threading dislocations intechnologically important InGaAs/GaAs/Ge/Si heterostructures areindeed different from that of thematrix. Site-specific atom probe tomography enabled by electron channeling contrast imaging reveals this at individual dislocations.We present evidence for the simultaneousfast diffusion of germanium and indium up and down adislocation, respectively, leading to unique compositional profiles. We also detect the formation of clusters of metastable composition at the interface between Ge and GaAs, driven by intermixing in these two nearly immiscible materials.Together,our results have important implications for the properties of dislocations and interfaces in semiconductors andprovide new tools for their study.

Diffusion of indium in single crystal zinc oxide: a comparison between group III donors

Dopant diffusion of indium (In) in single crystal zinc oxide is studied by secondary ion mass spectrometry and is interpreted using a reaction–diffusion model that invokes predictions from density functional theory (DFT). An apparent activation energy of 2.2 eV is obtained for the diffusion of In, when the local Fermi-level position is about 0.2 eV below the conduction band edge. The diffusion of In is found to be significantly faster that that reported for the other group III donors, aluminum and gallium, with several orders of magnitude higher effective diffusivities, that can be assigned to a lower migration barrier for the diffusion of In. Furthermore, our results reveal self-consistency in previous DFT results of defect formation- and migration energies. From this, the diffusion of In is suggested to occur through mobile charged zinc vacancies that form intermediate mobile ()− pairs. The pairs in turn dissociate rather readily at the studied temperatures (850 °C–1150 °C), which results in distinct and abrupt diffusion fronts for the In depth distribution profiles.

Effects of thermal and electrical stress on defect generation in InAs metal–oxide–semiconductor capacitor

Defects in HfO2 dielectric film caused by indium and arsenide diffusion from InAs were investigated. To investigate the dissociation of InAs during post-deposition annealing (PDA) at 600 °C, we analyzed the ratio of the elements on the surface of the oxide layer and the chemical states by using time-of-flight secondary-ion mass spectroscopy and X-ray photoelectron spectroscopy, respectively. In–As bonding was dissociated and In and As atoms were diffused through the HfO2 layer from InAs. Fortunately, the diffusion and trap density could be controlled by using a 1-nm-thick Al2O3 passivation layer.In addition, we used the nitridation process to control the trap density. We evaluated the thermal and electrical stability of three samples—HfO2/InAs, HfO2/Al2O3/InAs, and nitrided HfO2/Al2O3/InAs—by analyzing the change in trap density before and after PDA at 600 °C and the stress-induced leakage current. In conclusion, the passivation layer effectively improved the thermal and electrical stability, whereas the nitridation process using NH3 gas did not. Moreover, although nitridation could reduce the interfacial defect states, due to structure distortion, it induced the degradation of the device.

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.

ТЕРМИЧЕСКОЕ ОКСИДИРОВАНИЕ КАК СПОСОБ СОЗДАНИЯ НАНОРАЗМЕРНЫХ ФУНКЦИОНАЛЬНЫХ ПЛЕНОК НА ПОЛУПРОВОДНИКАХ AIIIBV: ХЕМОСТИМУЛИРУЮЩЕЕ ВОЗДЕЙСТВИЕ ОКСИДОВ МЕТАЛЛОВ ОБЗОР

Рассмотрены особенности хемостимулирующего воздействия оксидов металлов на процесс термооксидирования полупроводников AIIIBV. Установлено, что химическая природа оксида-хемостимулятора и способ его введения в систему (из газовой фазы или нанесение на поверхность полупроводника) определяют механизм процесса. Оксиды р-металлов (PbO, Sb2O3, Bi2O3) реализуют транзитный механизм оксидирования независимо от способа их введения в систему. Оксиды d-металлов (MnO2, V2O5, CrO3), вводимые через газовую фазу, выступают в роли хемостимуляторов-транзиторов. Воздействие наноразмерных слоев NiO и Co3O4 развивается по транзитному типу. Для нанесённых на поверхность полупроводника наноразмерных слоёв V2O5 механизм их воздействия на процесс оксидирования АIIIВV в значительной мере определяется методом нанесения (в рамках одного способа) – мягким или жёстким.
 
 Результаты исследований получены на оборудовании Центра коллективного пользования Воронежского государственного университета. URL: http://ckp.vsu.ru 
 Работа выполнена при поддержке гранта РФФИ № 16-43-360595 р_а

Sodium enhances indium-gallium interdiffusion in copper indium gallium diselenide photovoltaic absorbers

Copper indium gallium diselenide-based technology provides the most efficient solar energy conversion among all thin-film photovoltaic devices. This is possible due to engineered gallium depth gradients and alkali extrinsic doping. Sodium is well known to impede interdiffusion of indium and gallium in polycrystalline Cu(In,Ga)Se2 films, thus influencing the gallium depth distribution. Here, however, sodium is shown to have the opposite effect in monocrystalline gallium-free CuInSe2 grown on GaAs substrates. Gallium in-diffusion from the substrates is enhanced when sodium is incorporated into the film, leading to Cu(In,Ga)Se2 and Cu(In,Ga)3Se5 phase formation. These results show that sodium does not decrease per se indium and gallium interdiffusion. Instead, it is suggested that sodium promotes indium and gallium intragrain diffusion, while it hinders intergrain diffusion by segregating at grain boundaries. The deeper understanding of dopant-mediated atomic diffusion mechanisms should lead to more effective chemical and electrical passivation strategies, and more efficient solar cells.

Conductive bridge random access memory characteristics of SiCN based transparent device due to indium diffusion

In this work, the transparent bipolar resistive switching characteristics of a SiCN-based ITO/SiCN/AZO structure due to In diffusion from ITO is studied. The SiCN based device is found to be 80% transparent in the visible wavelength region. This device, with AZO as both top and bottom electrodes, does not show any RRAM property due to deposition of the high quality O2-free SiCN film. Replacing the AZO top electrode with ITO in this device results in good resistive switching (RS) characteristics with a high on/off ratio and long retention. Replacing the SiCN film with ZrO2 also results in excellent RS characteristics due to the formation of an oxygen vacancies filament inside the ZrO2 film. A resistance ratio of on/off is found to be higher in the SiCN based device compared to that of the ZrO2 device. Diffusion of In from ITO into the SiCN film on application of high positive voltage during forming can be attributed to the occurrence of RS in the device, which is confirmed by the analyses of energy dispersive spectroscopy and secondary-ion mass spectrometry. This study shows a pathway for the fabrication of CBRAM based transparent devices for non-volatile memory application.

Interfacial relaxation analysis of InGaAs/GaAsP strain-compensated multiple quantum wells and its optical property

InGaAs/GaAsP strain-compensated multiple quantum wells were prepared by metal organic chemical vapor deposition on GaAs (100) substrates with misorientation of 15° toward [111]. In order to obtain better strain-compensated abrupt heterojunction interfaces, the compressive strain and relaxation of different quantum well and the total accumulated strain were investigated by adjusting In composition and the thickness of InxGa1-xAs well and GaAs1-yPy barrier keep constant. High resolution X-ray diffraction results indicate the crystal and interfacial structures of In0.18Ga0.82As (7 nm)/GaAs1-yPy with the least relaxation and total strain mismatch are better than others. From in-situ surface reflectivity curves, we observed the slope of reflectivity curve of multiple quantum wells increases with increasing lattice relaxation. Atomic force microscopic results show surface morphologies of three samples are Volmer-Weber mode. Indium segregation at heterointerface between well and barrier were investigated by secondary ion mass spectrometry which indicate indium diffusion width increase with the increasing total strain mismatch. Finally, a shoulder peak was observed from Gaussian fitting of photoluminescence, stemming from the lattice relaxation. These results demonstrate that the relaxation process is introduced and indium segregation length widens as the relaxation increases. The experimental results will be favorable for optimizing the epitaxial growth of InGaAs/GaAsP strain-compensated quantum wells in order to obtain high quality smooth heterointerface.

Effect of sulfurization on the properties of Cu2ZnSnS4 thin films deposited using chemical spray pyrolysis over ITO substrates

Cu2ZnSnS4 thin films with different tin concentration are deposited over ITO coated glass substrates using chemical spray pyrolysis technique, by adjusting [Sn][Zn] ratio as 0.7, 1 and 1.3 in the precursor solution. As prepared films are subjected to sulfurization at a temperature of 500°C for 15min and its effect on the structure and composition of the films is studied. Sulfurization is carried out under non-vacuum condition inside the spray pyrolysis chamber making it compatible with the deposition technique. Pristine and sulfurized films are analysed using X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy, UV–Vis–NIR spectroscopy and scanning electron microscopy. X-ray diffraction and Raman spectroscopy suggest the formation of Cu2ZnSnS4 and other binary compounds in the pristine films. Analysis of the sulfurized films indicates that the sulfurization process has brought about a significant change in the composition of the films while improving its crystallinity considerably. Compositional analysis using X-ray photoelectron spectroscopy reveals that substantial amount of indium from the underlying ITO has diffused into the film after sulfurization. However, it is observed that increase in concentration of tin in the film limits the diffusion of indium. Scanning electron microscopic images show the improvement in morphology of the films after sulfurization.

A technique for the local doping and correction of the conductivity of PbSnTe epitaxial layers via indium diffusion from superficial nanometer-thick films

A technique is described for the local indium doping of epitaxial films of a p-type PbSnTe solid solution to obtain a metal-insulator transition at liquid-helium temperatures. The indium was diffused from the surface of the film, from an In layer several nanometers thick, whereas the shape and size of the doped layer were set by a mask. It is emphasized that the oxide layer should be removed before indium deposition, and that the thickness of the deposited indium layer should be precisely chosen based on the thickness of the PbSnTe film. The results of using this technique for films having different compositions and the results of measurements performed on a planar p-i-p structure are considered.

Surface diffusion measurements of In on InGaAs enabled by droplet epitaxy

Surface diffusion is a critical parameter for non-equilibrium growth techniques such as molecular beam epitaxy. However, very little is known about diffusion rates of individual cations in a mixed cation material. Using droplet epitaxy as the growth technique, we isolate the diffusivity prefactor (D0) and activation energy (EA) of indium on the surface of In0.53Ga0.47As/InP(100). We report two regimes of indium diffusivity under As2-rich conditions: above and below the droplet deposition temperature of 300 °C, corresponding to a change in surface reconstruction. We also discuss methods of extracting the indium diffusion parameters on metal-rich surfaces using droplet epitaxy and nucleation theory. The obtained diffusion parameters are compared to previous work in the literature and could be employed to optimize growth conditions for non-equilibrium crystal growth.

Modification of the surface of GaAs and observation of surface enhanced Raman scattering after the diffusion of indium

The results of studies of the surface of GaAs in the presence of indium and phosphorus surfactants are reported. It is shown that, as a result of their diffusion (annealing) at a temperature of 650–670°C, clusters enriched with indium are formed in the GaAs surface region. The clusters can be seen as bright spots in an image obtained by a scanning electron microscope with the use of an in-lens detector. At the same time, studies of the morphology of this surface with an atomic-force microscope show a decrease in the root-meansquare roughness of the surface after annealing (diffusion), which is indicative of the incorporation of In atoms into the GaAs crystal lattice. The clusters are responsible for changes in the Raman spectra. Specifically, an increase in the signal intensity due to surface-enhanced Raman scattering and a shift of the vibration frequency in the surface region are observed. It is found that cluster formation is defined by the crystallographic orientation of the surface and by the technological conditions of surface preparation.

Effect of a magnetron-sputtered MnO2 layer on the thermal oxidation kinetics of InP and the composition and morphology of the resultant films

It has been shown in the process of optimization of approaches to effective control over the formation of functional nanofilms on III–V semiconductors that the surface modification of InP with magnetronsputtered MnO2 nanolayers (25 nm thick) results in an oxygen transfer mechanism of the thermal oxidation of the semiconductor. The advantages of this approach are a higher rate of the increase in film thickness in comparison with stimulator-free oxidation, rapid chemical binding of indium, blocking of indium diffusion into the film, and accelerated phosphate formation. Changes in the composition of the films in comparison with those produced by stimulator-free oxidation lead to a considerable improvement in their surface quality (the roughness height does not exceed 20 nm and the average grain size is 55 nm).

Layer by layer characterisation of the degradation process in PCDTBT:PC71BM based normal architecture polymer solar cells

This work demonstrates the stability and degradation of OSCs based on poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′ benzothiadiazole)] (PCDTBT): (6,6)-Phenyl C71 butyric acid methyl ester (PC71BM) photoactive blend layers as a function of ageing time in air. Analysis of the stability and degradation process for the OSCs was conducted under ambient air by using current-voltage (I-V) measurements and x-ray photoelectron spectroscopy (XPS). The interface between photoactive layer and HTL (PEDOT:PSS) was also investigated. Device stability was investigated by calculating decay in power conversion efficiency (PCE) as a function of ageing time in the air. The PCE of devices decrease from 5.17 to 3.61% in one week of fabrication, which is attributed to indium and oxygen migration into the PEDOT:PSS and PCDTBT:PC71BM layer. Further, after aging for 1000 h, XPS spectra confirm the significant diffusion of oxygen into the HTL and photoactive layer which increased from 3.0 and 23.3% to 20.4 and 35.7% in photoactive layer and HTL, respectively. Similarly, the indium content reached to 17.9% on PEDOT:PSS surface and 0.4% on PCDTBT:PC71BM surface in 1000 h. Core-level spectra of active layer indicate the oxidation of carbon atoms in the fullerene cage, oxidation of nitrogen present in the polymer matrix and formation of In2O3 due to indium diffusion. We also observed a steady fall in the optical absorption of the active layer during ageing in ambient air and it reduced to 76.5% of initial value in 1000 h. On the basis of these experimental results, we discussed key parameters that account for the degradation process and stability of OSCs in order to improve the device performance.

Epitaxy and optical properties of InGaN/GaN multiple quantum wells on GaN hexagonal pyramids template

The InGaN/GaN multiple quantum wells (MQWs) with truncated pyramid structure have been successfully epitaxially grown on the GaN hexagonal pyramids template through a simple and low-cost etch-regrown process. GaN hexagonal pyramids template was contained by a convenient photo-assisted chemical (PAC) etching method. The truncated pyramids are composed of {101¯1¯} and {112¯2} semi-polar facets as well as (0001) polar facet. It was observed that the InGaN/GaN MQWs substantially emitted broad spectrum with multiple peaks by room temperature photoluminescence (PL). The cathodoluminescence of MQWs red-shifts as the location moves from bottom to top on the facets due to the indium diffusion mechanism.

On the thermal oxidation of V x O y –InP heterostructures formed by the centrifugation of vanadium(V) oxide gel

The optimal mode for the application of a nanoscale layer of vanadium-pentoxide gel on the surface of indium phosphide by centrifugation is determined via spectroscopic ellipsometry and atomic-force microscopy. By oxidizing the formed VxOy—InP heterostructures, films are obtained with a grain structure, with the height of the relief not exceeding 70 nm. The presence of incompletely oxidized chemostimulator components (VO2, V2O3) in the films and the presence of InVO4, which binds the V2O5 chemostimulator and thereby blocks the regeneration cycle of V+5 ↔ V+4, suggest implementation of the transit mechanism of the chemostimulated oxidation of indium phosphide. The data of spectroscopic ellipsometry indicate incomplete kinetic blocking of the diffusion of indium into the films upon oxidation.

Degradation of organic light emitting diode: Heat related issues and solutions

Degradation of organic light emitting diodes (OLEDs) is the most serious obstacle towards their commercialization. OLED degrades due to various internal and external mechanisms. External degradation is mainly caused due to the instability of low work function cathode, pin-hole formation during fabrication which provides a path for oxygen and moisture infiltration. Operation of OLED also leads to degradation with major causes being morphological instability of organic layers, trap formation, indium or oxygen diffusion from anode, interface deterioration etc. Heat generation in the OLED also acts as a source of degradation. Most of the heat is generated instantaneously upon biasing of OLED due to resistive or Joule heating as a consequence of high resistance of organic layers and non-radiative recombination. Generated heat can be reduced by reducing the effects of the generation sources such as improving conductivity of organic layers by doping, using additional layers to improve charge injection, employing emissive layers with low recombination losses etc. However, these ways can only reduce the heat up to a certain amount. To further improve the lifetime of OLED, the generated heat can be dissipated by employing heat sinks using either thermally conducting substrate or encapsulation etc. We present a review on OLED degradation with a particular focus on heat generation, its consequences and ways of reduction.

Increased carrier mobility and lifetime in CdSe quantum dot thin films through surface trap passivation and doping.

Passivating surface defects and controlling the carrier concentration and mobility in quantum dot (QD) thin films is prerequisite to designing electronic and optoelectronic devices. We investigate the effect of introducing indium in CdSe QD thin films on the dark mobility and the photogenerated carrier mobility and lifetime using field-effect transistor (FET) and time-resolved microwave conductivity (TRMC) measurements. We evaporate indium films ranging from 1 to 11 nm in thickness on top of approximately 40 nm thick thiocyanate-capped CdSe QD thin films and anneal the QD films at 300 °C to densify and drive diffusion of indium through the films. As the amount of indium increases, the FET and TRMC mobilities and the TRMC lifetime increase. The increase in mobility and lifetime is consistent with increased indium passivating midgap and band-tail trap states and doping the films, shifting the Fermi energy closer to and into the conduction band.

Heterointegration of InGaAs/GaAs quantum wells on micro-patterned Si substrates

InGaAs/GaAs quantum wells (QWs) grown on μ-patterned Ge/Si substrates by metal organic vapor phase epitaxy are investigated by electron microscopy and spatially resolved photoluminescence (PL) spectroscopy. The lattice parameter mismatch of GaAs and Si is overcome by a Ge buffer layer grown by low-energy plasma enhanced chemical vapor deposition. The GaAs crystals form truncated pyramids whose shape is strongly affected by the geometry of the underlying pattern consisting of 8 μm deep and 3–50 μm wide square Si pillars. Comparing the measured PL energies with calculations performed in the effective mass approximation reveals that the QW emission energies are significantly influenced by the GaAs morphology. It is shown that the geometry favors indium diffusion during growth from the inclined facets towards the top (001) facet. The Si pillar-size dependent release of thermally induced strain observed in the PL measurements is confirmed by X-ray diffraction.

General observation of the memory effect in metal-insulator-ITO structures due to indium diffusion

Resistive random access memory (RRAM) devices based on metal oxides, organic molecules and inorganic nanocrystals (NCs) have been studied extensively in recent years. Different memory switching mechanisms have been proposed and shown to be closely related to the device architectures. In this work, we demonstrate that the use of an ITO/active layer/InGa structure can yield nonvolatile resistive memory behavior in a variety of active materials, including polymers, organic small molecules, and colloidal NCs. Through the electrode material and thickness-dependent study, we show that the ON state of the devices is associated with filamentary conduction induced by indium diffusion from the ITO electrode, occurring mostly within around 40–50 nm from the ITO/active layer interface. A negative differential resistance (NDR) regime is observed during transition from the ON to OFF state, and is explained by the space charge limited current (SCLC) effect due to hole injection at the ITO/active layer interface. Our study reveals the impact of indium diffusion at the ITO/active layer interface, an important factor that should be taken into consideration when designing thin printed RRAM devices.