Indium Diffusion Research Articles

Analog and digital resistive switching in W/TiO2/ITO devices: the impact of crystallinity and Indium diffusion

The resistance-switching memristor with capabilities of information storage and brain-inspired computing has prime importance in recent research. In this study, the impact of crystallinity and Indium diffusion on the existence of analog and digital resistive switching in a W/TiO2/ITO device has been reported. The memristor devices are fabricated by depositing titania films by sol–gel and spin-coating techniques. The films annealed at 250 °C and 400 °C were characterized using x-ray diffraction, Raman spectroscopy, scanning electron microscopy, and x-ray photoelectron spectroscopy (XPS). The characteristic anatase phase started appearing after annealing at 400 °C, whereas the 250 °C annealed sample was in the amorphous state. The electrical characterization revealed significant differences in the switching characteristics of amorphous and crystalline samples, especially in the switching interface, compliance properties, and current conduction mechanism. The grain boundary assisted oxygen vacancy migration, and the diffusion of indium ions from the ITO bottom electrode helped the crystalline sample to show highly stable and reproducible resistive switching compared to amorphous film. The XPS studies confirmed the indium ion diffusion in the crystalline sample. The oxygen vacancy-induced barrier modulation and conductive filament formation caused characteristic switching in amorphous and crystalline samples, respectively. Schottky emission in the amorphous film and SCLC mechanism in the crystalline film confirmed the experimental results. This study provides a distinctive viewpoint and an innovative strategy for developing multifunctional resistive switching devices.

МЕХАНІЗМИ МАСОПЕРЕНОСУ ІНДІЮ В Cd(Zn)Te ПРИ ДІЇ НАНОСЕКУНДНИХ ЛАЗЕРНИХ ІМПУЛЬСІВ

The processes of heating, melting and ablation during nanosecond laser irradiation of metal film (In) / CdTe structures and CdZnTe solid solutions are considered. Time and coordinate (in depth) temperature profiles during nanosecond laser irradiation of the system the film In/CdTe were calculated. Melting thresholds of indium and CdTe in the In/CdTe film system have been established. The profile of the distribution of indium atoms in cadmium telluride after a single laser irradiation of the In/CdTe structure, accompanied by the formation of an inversion layer (n-type), was obtained and theoretically described; a peak at a depth of 6 nm was detected. The mass transfer coefficients of indium in CdTe in different regions were determined during nanosecond laser irradiation of the In/CdTe structure with a thickness of the In film of 30 nm on the metal side at Epad = 100 mJ/cm2. It was established that the mass transfer coefficient of In atoms in CdTe during nanosecond laser irradiation of the In/CdTe film structure depends on the distance from the CdTe surface and increases, which is associated with a rapid change over time in the inhomogeneous deformation of the crystal lattice in the process of indium diffusion. The obtained value of the coefficient of laser-induced mass transfer of In in CdTe by an order of magnitude is much higher than the diffusion coefficients of impurities under normal annealing conditions with the diffusion method of impurity introduction and is commensurate with the self-diffusion coefficient in a number of liquid metals.

Insights into thermodynamic destabilization in Mg-In-D hydrogen storage system: A combined synchrotron X-ray and neutron diffraction study

In this study, ultrafine Mg(In) solid-solution particles were successfully prepared through an arc plasma method and their deuterium uptake/release performances were systematically estimated with respect to the identically processed pure Mg particles. Thermodynamic destabilization and kinetic enhancement of Mg-In-D system were achieved simultaneously with lower deuterium ab/desorption enthalpies and decreased desorption temperatures. For the first time, an in-situ synchrotron X-ray diffraction (ISXRD) coupled with neutron powder diffraction (NPD) technique and density functional theory (DFT) calculations clearly substantiated that an indium diffusion-dominated phase transition is the driving force for the evolution from mixture of MgD2 and Mg-In intermetallic to Mg-based solid solution during the deuterium release (DR). The ISXRD results clarified the real-time phase transition from MgIn to Mg3In at 515 K and the interreaction of MgD2 and Mg3In at 640 K, by which the matrix could be destabilized to trigger an indium-diffusion governed DR reaction in deuteride. Moreover, with the aid of NPD experiment, the microstructure evolution of Mg-In-D system demonstrated the continuous diffusion of indium into Mg/MgD2 upon desorption. The solubilized indium in MgD2 effectively reduced the D-migration energy barrier and stabilized the lattice structure to restrain the constriction of Mg-D bonds, through which the noticeable improvement on both thermodynamic and kinetic performances of the Mg-In system was achieved. The combination of synchrotron X-ray and neutron diffraction offers a high-efficiency strategy to fathom the hydrogen discharging mechanism from the viewpoint of real-time phase transitions and crystalline structure evolutions.

Atomic Diffusion of Indium through Threading Dislocations in InGaN Quantum Wells.

The compositional and structural investigations of threading dislocations (TDs) in InGaN/GaN multiple quantum wells were carried out using correlative transmission electron microscopy (TEM) and atom probe tomography (APT). The correlative TEM/APT analysis on the same TD reveals that the indium atoms are diffused along the TD and its concentration decreases with distance from the InGaN layer. On the basis of the results, we directly observed that the indium atoms originating from the InGaN layer diffuse toward the epitaxial GaN surface through the TD, and it is considered to have occurred via the pipe diffusion mechanism induced by strain energy relaxation.

Texture evolution mechanism of pulsed laser deposited in-doped Ga2O3 film affected by laser fluence and its application in solar-blind photodetector

This work explored the crystal structural, optical bandgap, and morphological texture evolution of pulsed laser deposited In-doped Ga2O3 films grown on sapphire substrate at different laser fluence from 1.0 to 2.6 J/cm2. The in situ optical emission spectroscopy was carried out to monitor the plasma radicals generated during the deposition. All the deposited films were crystallized and some clusters were formed because of high deposition temperature and rapid surface diffusion of indium (In). The growth rate and the crystallinity of the film increased and then declined with increasing laser fluence. The texture evolution mechanism of the films has been proposed firstly. The rapid diffusion of In, the sputtering and reflection effect of plasma species exist in whole films’ deposition process, which has a significant impact on the texture characteristics of the films. The clusters emerging on film surface were the crystallized In-rich InGaOx nanoparticles consisting of β-Ga2O3 and cubic In2O3 phases. Metal-semiconductor-metal solar-blind photodetectors were also fabricated and analyzed to illustrate the effect of laser fluence. The elaboration of texture evolution mechanism and effect of laser fluence on the properties of the In-doped Ga2O3 films and photodetectors is very beneficial for its application in high performance photoelectric devices.

Towards 3D characterisation of site-controlled InGaAs pyramidal QDs at the nanoscale

In this work, we report an extensive investigation via transmission electron microscopy (TEM) techniques of InGaAs/GaAs pyramidal quantum dots (PQDs), a unique site-controlled family of quantum emitters that have proven to be excellent sources of single and entangled photons. The most striking features of this system, originating from their peculiar fabrication process, include their inherently 3-dimensional nature and their interconnection to a series of nanostructures that are formed alongside them, such as quantum wells and quantum wires. We present structural and chemical data from cross-sectional and plan view samples of both single and stacked PQDs structures. Our findings identify (i) the shape of the dot, being hexagonal and not triangular as previously assumed, (ii) the chemical distribution at the facets and QD area, displaying clear Indium diffusion, and (iii) a near absence of Aluminium (from the AlAs marker) at the bottom of the growth profile. Our results shed light on previously unreported structural and chemical features of PQDs, which is of extreme relevance for further development of this family of quantum emitters.Graphical abstract

Sol–Gel-Derived Cu-Doped ZnO Thin Films for Optoelectronic Applications

Pristine and Cu-doped ZnO thins films were deposited on Si(100) and quartz substrates by the sol–gel method, followed by post annealing at 450 °C. Structural analysis shows that all grown films are polycrystalline in nature and the crystallite size of the doped film increases with the doping concentration. Narrowing of the band gap is seen with Cu doping, and electrical analysis shows an increase in the conductivity and carrier concentration with Cu doping. As compared to pristine ZnO, Cu-doped thin films show p-type conductivity with a maximum carrier concentration of 1.34 × 1015 cm–3 for 6% doping at room temperature. The p-type conductivity in these films easily degraded with time, which may be due to the interaction of films with ambient conditions or may be due to the diffusion of indium inside the material. After 15 days, ambient-exposed films were totally converted into n-type, whereas the vacuum-placed film still shows p-type behavior with good mobility. This study shows that sol–gel-derived Cu-doped thin films show low electrical resistivity, p-type conductivity, and high transmittance and can be used for optoelectronics devices if these films were well prepared, protected, and properly passivated.

Influence of atom segregation on the structure and luminescence of InGaAsSb/AlGaAsSb multiple quantum wells

Quaternary Indium gallium arsenic antimony (InGaAsSb) compounds is indispensable as the active layer of diode lasers emitting at 1.75–4.4 μm, which are used in optoelectronic devices. However, the course of the high-temperature instability of the quantum well structure, which is closely related to the diffusion of indium (In) and antimony (Sb) atoms, is still not clear due to the system's complexity. In this paper, the diffusion process of indium and antimony atoms by thermal treatment, and the changes in the structural and optical properties of the InGaAsSb/AlGaAsSb multiple quantum wells (MQWs) were investigated. The InGaAsSb/AlGaAsSb MQWs were treated with a treatment time of 40 s at different annealing temperatures. X-ray diffraction (XRD) and Raman spectra show that with the increase of annealing temperature, the structure of MQWs were destroyed more seriously, and the segregation of indium and antimony becomes more serious. The luminescence characteristics of MQWs with component segregation were investigated by photoluminescence (PL) spectra.

Improved device efficiency and lifetime of perovskite light-emitting diodes by size-controlled polyvinylpyrrolidone-capped gold nanoparticles with dipole formation

Herein, an unprecedented report is presented on the incorporation of size-dependent gold nanoparticles (AuNPs) with polyvinylpyrrolidone (PVP) capping into a conventional hole transport layer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The hole transport layer blocks ion-diffusion/migration in methylammonium-lead-bromide (MAPbBr3)-based perovskite light-emitting diodes (PeLEDs) as a modified interlayer. The PVP-capped 90 nm AuNP device exhibited a seven-fold increase in efficiency (1.5%) as compared to the device without AuNPs (0.22%), where the device lifetime was also improved by 17-fold. This advancement is ascribed to the far-field scattering of AuNPs, modified work function and carrier trapping/detrapping. The improvement in device lifetime is attributed to PVP-capping of AuNPs which prevents indium diffusion into the perovskite layer and surface ion migration into PEDOT:PSS through the formation of induced electric dipole. The results also indicate that using large AuNPs (> 90 nm) reduces exciton recombination because of the trapping of excess charge carriers due to the large surface area.

Origin of operating voltage increase in deep UV light-emitting diodes with ITO/Al reflector

In an attempt to further elucidate the operating voltage increase in a vertical UV-C LED with p-electrode composed of transparent conducting Sn-doped indium oxide (ITO)/Al reflector, the interface formation between ITO and Al thin film was studied by using scanning transmission electron microscopy in combination with electron energy loss spectroscopy. It was confirmed that the oxidized layer was formed at the interface of the ITO/Al electrode in accordance with the thermal annealing. It was found that not only the thickness of oxide formation grew with the increased annealing temperature, the content of oxygen also increased. Moreover, it was also ascertained that the prolonged annealing time at high temperature induced the indium diffusion into the Al-oxide layer.

Bias Polarity Dependent Threshold Switching and Bipolar Resistive Switching of TiN/TaOx/ITO Device

In this work, we demonstrate the threshold switching and bipolar resistive switching with non-volatile property of TiN/TaOx/indium tin oxide (ITO) memristor device. The intrinsic switching of TaOx is preferred when a positive bias is applied to the TiN electrode in which the threshold switching with volatile property is observed. On the other hand, indium diffusion could cause resistive switching by formation and rupture of metallic conducting filament when a positive bias and a negative bias are applied to the ITO electrode for set and reset processes. The bipolar resistive switching occurs both with the compliance current and without the compliance current. The conduction mechanism of low-resistance state (LRS) and high-resistance state (HRS) are dominated by Ohmic conduction and Schottky emission, respectively. Finally, threshold switching and bipolar resistive switching are verified by pulse operation.

Indium segregation mechanism and V-defect formation at the [0001] InAlN surface: an ab-initio investigation

First-principle calculations were performed to investigate adsorption and diffusion of indium and aluminum atoms on (0001) and (0001) In (18%) AlN surfaces. First, it was shown that these surfaces are most stable when they contain complex defects. The presence of vacancies causes the In to be strongly bound to the surface with the adsorption energy increasing by 0.11 eV for metal-polar and by 0.78 eV N-polar. In contrast, the adsorption strength of Al to the surface with defects decreases; the corresponding energy goes from 3.96 eV–2.29 eV (metal-polar) and from 8.30 eV–5.05 eV (N-polar). Simultaneously, the diffusion of In is enhanced; its energy barrier decreases by 0.74 eV (0.06 eV) for the N-polar (metal-polar) InAlN surface, whereas that of the Al adatom increases by 0.32 eV for metal-polar (0.08 eV for N-polar), which should limit its diffusion on the surface. Therefore, the indium atoms will tend to migrate towards the complex defects. Eventually, during epitaxial growth, this aggregation of indium atoms around the defects and the low mobility of Al atoms could be the origin of the observed V defects, the phase separation and the crystallographic degradation of the InAlN epitaxial layers with increasing thickness.

Improved water oxidation performance of ultra-thin planar hematite photoanode: Synergistic effect of In/Sn doping and an overlayer of metal oxyhydroxides

Hematite is a promising photoanode candidate with many favorable material properties, such as stability and suitable band-gap. However, there are some severe challenges, including high losses due to charge recombination and slow oxidation kinetics, which can be addressed by doping and addition of co-catalysts. Here, the effects of temperature driven diffusion of substrate impurities (doping) and subsequent surface modification by metal oxy-hydroxides (co-catalysts) have been studied for enhanced water-oxidation performance in photoelectrochemical (PEC) measurements. Diffusion of indium and tin from the indium-doped tin oxide (ITO) substrate into planar films of α-Fe2O3 photoanodes results in a photocurrent density (Jph) of 0.09 mA/cm2, corresponding to an approximate 9-fold enhancement over the control pristine α-Fe2O3 (0.01 mA/cm2) at 1.23 VRHE. A thin amorphous FeOOH coating over the In/Sn co-doped α-Fe2O3 photoanode improves the water oxidation performance further, with a 211 % enhancement in Jph at 1.23 VRHE and a 0.21 V cathodic shift in onset potential. Thin layers of NiOOH and FeNiOOH co-catalysts exhibit 100 and 155 % enhancement in Jph, respectively. Characterization and electrochemical measurements reveal that the enhanced performance is a result of reduced bulk recombination by temperature driven In/Sn substrate impurity doping and improved surface oxidation kinetics by the metal oxy-hydroxide overlayer. Especially deposition of FeOOH onto In/Sn co-doped α-Fe2O3 significantly reduces resistance at the semiconductor/electrolyte interface, leading to the shift in onset potential. Further, the results indicate that all the samples exhibit a quantitative correlation between the cathodic shift in photocurrent onset potential (Vonset) and flat band potential (Vfb).

Conductance spectra of (Nb, Pb, In)/NbP superconductor/Weyl semimetal junctions

The possibility of inducing superconductivity in type-I Weyl semimetal through coupling its surface to a superconductor was investigated. A single crystal of NbP, grown by chemical vapor transport method, was carefully characterized by XRD, EDX, SEM, ARPES techniques and by electron transport measurements. The mobility spectrum of the carriers was determined. For the studies of interface transmission, the (001) surface of the crystal was covered by several hundred nm thick metallic layers of either Pb, or Nb, or In. DC current-voltage characteristics and AC differential conductance through the interfaces as a function of the DC bias were investigated. When the metals become superconducting, all three types of junctions show conductance increase, pointing out the Andreev reflection as a prevalent contribution to the subgap conductance. In the case of Pb-NbP and Nb-NbP junctions, the effect is satisfactorily described by modified Blonder-Tinkham-Klapwijk model. The absolute value of the conductance is much smaller than that for the bulk crystal, indicating that the transmission occurs through only a small part of the contact area. An opposite situation occurs in In-NbP junction, where the conductance at the peak reaches the bulk value indicating that almost whole contact area is transmitting and, additionally, a superconducting proximity phase is formed in the material. We interpret this as a result of indium diffusion into NbP, where the metal atoms penetrate the surface barrier and form very transparent superconductor-Weyl semimetal contact inside. However, further diffusion occurring already at room temperature leads to degradation of the effect, so it is observed only in the pristine structures. Despite of this, our observation directly demonstrates possibility of inducing superconductivity in a type-I Weyl semimetal.

Synergies of co-doping in ultra-thin hematite photoanodes for solar water oxidation: In and Ti as representative case.

Solar energy induced water splitting in photoelectrochemical (PEC) cells is one of the most sustainable ways of hydrogen production. The challenge is to develop corrosion resistant and chemically stable semiconductors that absorb sunlight in the visible region and, at the same time, have the band edges matching with the redox level of water. In this work, hematite (α-Fe2O3) thin films were prepared onto an indium-doped tin oxide (ITO; In:SnO2) substrate by e-beam evaporation of Fe, followed by air annealing at two different temperatures: 350 and 500 °C. The samples annealed at 500 °C show an in situ diffusion of indium from the ITO substrate to the surface of α-Fe2O3, where it acts as a dopant and enhances the photoelectrochemical properties of hematite. Structural, optical, chemical and photoelectrochemical analysis reveal that the diffusion of In at 500 °C enhances the optical absorption, increases the electrode–electrolyte contact area by changing the surface topology, improves the carrier concentration and shifts the flat band potential in the cathodic direction. Further enhancement in photocurrent density was observed by ex situ diffusion of Ti, deposited in the form of nanodisks, from the top surface to the bulk. The in situ In diffused α-Fe2O3 photoanode exhibits an improved photoelectrochemical performance, with a photocurrent density of 145 μA cm−2 at 1.23 VRHE, compared to 37 μA cm−2 for the photoanode prepared at 350 °C; it also decreases the photocurrent onset potential from 1.13 V to 1.09 V. However, the In/Ti co-doped sample exhibits an even higher photocurrent density of 290 μA cm−2 at 1.23 VRHE and the photocurrent onset potential decreases to 0.93 VRHE, which is attributed to the additional doping and to the surface becoming more favorable to charge separation.

Overcoming consistency constrains of ITO/ZnO/P3HT:PCBM/Ag solar cell by open air annealing and its systematic stability study under inborn conditions

Focusing on simplicity and industrial viability, polymer solar cells with configuration indium tin oxide (ITO)/ZnO/P3HT:PCBM/Ag were fabricated and characterized. Differing from the usual trend of using glove box for polymer device fabrication, here electron transport and active layer of the devices were deposited and stored in open air atmosphere without any encapsulation. Effect of active layer thickness on device performance was analyzed. Choosing the optimum thickness of 220 ± 20 nm, a number of devices were fabricated with same configuration and the effect of annealing on the photovoltaic parameters was investigated. Unlike annealing studies reported in literature, particular emphasis was given here to study the influence of annealing in ambient atmosphere, at temperature of 50 °C, for 30 s. This short period, low temperature annealing enhanced the device parameters mainly short circuit current density and hence efficiency. Lifetime measurements were done by monitoring the device and measuring its J–V parameters periodically for 1 year. X-ray photoelectron spectroscopy depth profile analysis was employed to demonstrate that surface modified ZnO effectively hinders the diffusion of indium from ITO to active layer.

Indium Diffusion Behavior and Application in HfO2‐Based Conductive Bridge Random Access Memory

This study proposes the design of conductive bridge random access memory (CBRAM) using an indium electrode, which diffuses into hafnium oxide. The device is found to exhibit good operating characteristics, maintaining a large operation window, low set and reset voltages, and advantageous operation speed, thereby reducing operating power consumption. Electrical experiments, transmission electron microscopy, and energy‐dispersive spectroscopy confirm that the device exhibits the characteristics of a CBRAM device. In addition, due to the large operation window of this In electrode device, a combination of two of these CBRAM can act as a complementary resistive switching (CRS) device with a large memory window.

Feasibility of a high stable PbTe:In semiconductor for thermoelectric energy applications

High-efficiency thermoelectric conversion is achieved by using materials with a maximum figure of merit Z = S2σ/κ, where S is the Seebeck coefficient, and σ and κ are the electrical conductivity and thermal conductivity, respectively, over a wide temperature range. Lead telluride alloys were some of the first materials investigated and commercialized for generators; however, their full potential for thermoelectrics has only recently been revealed to be greater than commonly believed. The maximal value of Z, as a function of electron density, is attained only for a specific location of the Fermi level EF relative to the conduction band edge EC. A systematic study of structural, microstructural, and thermoelectric properties of bulk PbTe doped with indium is presented. Samples were prepared by the pulsed electric current sintering technique. The high dimensionless figure of merit ZT ≈ 0.8 over 200–500 °C temperature range for PbTe doped with 0.05–0.1 at. % of In was obtained. Moreover, ZT is practically the same for Pb0.9995In0.0005Te and Pb0.99In0.01Te compounds at high temperature. Therefore, indium dopant in PbTe stabilizes the optimal location of the Fermi level. The effect of the negative process of indium diffusion into the matrix during the long service time of the TE generator could be avoided by doping heavily with indium the hot side of n-type functionally graded PbTe:In leg.

Nitride-Derived Copper Modified with Indium as a Selective and Highly Stable Catalyst for the Electroreduction of Carbon Dioxide.

The lack of efficient catalysts prevents the electrocatalytic reduction of carbon dioxide from contributing to the pressing target of a carbon‐neutral economy. Indium‐modified copper nitride was identified as a stable electrocatalyst selective toward CO. In2O3/Cu3N showed a Faradaic efficiency of 80 % at 0.5 V overpotential for at least 50 h, in stark contrast to the very limited stability of the benchmark In2O3/Cu2O. Microfabricated systems allowed to correlate activity with highly stable interfaces in indium‐modified copper nitride. In contrast, fast diffusion of indium resulted in rapidly evolving interfaces in the case of the system based on oxide‐derived Cu. A metastable nitrogen species observed by spectroscopic means was proposed as the underlying cause leading to the unchanging interfaces. This work reveals the stabilizing properties of nitride‐derived copper toward high‐performance multicomponent catalysts.

Characterization studies of NiO:K anode buffer layer in Alq3 and TADF-based organic light-emitting diodes by secondary ion mass spectrometry and admittance spectroscopy

In this paper, we used thermal evaporation method to deposit metal oxide films as inorganic buffer layer in Organic light-emitting diodes (OLEDs), and investigated how the K2CO3-doped NiO (KNO) buffer layers affect OLEDs’ performances. The mechanisms of enhanced hole injection into the hole transport layer NPB (α-naphthylphenylbiphenyl diamine) via NiO:K2CO3 anode buffer layers in Alq3-based and TADF-based OLEDs were studied by means of J-V-L characteristics, secondary ion mass spectroscopy (SIMS), and admittance spectroscopy measurements. For Alq3-based OLEDs, devices’ opto-electrical performances showed increased of luminance from 8780 cd/m2 to 22940 cd/m2, the decreased of turn-on voltage from 3.4 V to 3.1 V at 1 mA/cm2, and increased of current efficiency from 4.3 cd/A to 3.48 cd/A when 1-nm-thick K2CO3-doped NiO film with doping concentration of 1 mol% was inserted into OLEDs. TADF-based OLEDs’ current efficiency increased from 21.7 cd/A to 29.7 cd/A with similar anode buffer layer parameters. SIMS depth profiles on OLEDs suggested higher indium (In) diffusion from ITO anode onto TADF-based OLEDs upon device operation leading to higher roll-off phenomenon. Deposition of NiO:K2CO3 as anode buffer layer onto OLEDs device reduced the diffusion of In in organic layers during device operation. Investigation of the capacitance as function of voltage and frequency yield information about carrier injection characteristics for both Alq3 and TADF-based OLEDs. Due to better carrier recombination capability, TADF-based OLEDs’ slope in V > Vbi area has fewer shifts and more stable response, leading to higher amplitude in current efficiency enhancement in comparison with fluorescents (Alq3) material.