Indium Diffusion Research Articles

Nanostructure and strain in InGaN/GaN superlattices grown in GaN nanowires

The structural properties and the strain state of InGaN/GaN superlattices embedded in GaN nanowires were analyzed as a function of superlattice growth temperature, using complementary transmission electron microscopy techniques supplemented by optical analysis using photoluminescence and spatially resolved microphotoluminescence spectroscopy. A truncated pyramidal shape was observed for the 4 nm thick InGaN inclusions, where their () central facet was delimited by six-fold {} facets towards the m-plane sidewalls of the nanowires. The defect content of the nanowires comprised multiple basal stacking faults localized at the GaN base/superlattice interface, causing the formation of zinc-blende cubic regions, and often single stacking faults at the GaN/InGaN bilayer interfaces. No misfit dislocations or cracks were detected in the heterostructure, implying a fully strained configuration. Geometrical phase analysis showed a rather uniform radial distribution of elastic strain in the () facet of the InGaN inclusions. Depending on the superlattice growth temperature, the elastic strain energy is partitioned among the successive InGaN/GaN layers in the case of low-temperature growth, while at higher superlattice growth temperature the in-plane tensile misfit strain of the GaN barriers is accommodated through restrained diffusion of indium from the preceding InGaN layers. The corresponding In contents of the central facet were estimated at 0.42 and 0.25, respectively. However, in the latter case, successful reproduction of the experimental electron microscopy images by image simulations was only feasible, allowing for a much higher occupancy of indium adatoms at lattice sites of the semipolar facets, compared to the invariable 25% assigned to the polar facet. Thus, a high complexity in indium incorporation and strain allocation between the different crystallographic facets of the InGaN inclusions is anticipated and supported by the results of photoluminescence and spatially resolved microphotoluminescence spectroscopy.

Studies on CdTe solar cell front contact properties using X-ray photoelectron spectroscopy

The chemical changes between transparent conducting oxide (TCO) and cadmium sulphide (CdS) layers were analyzed using X-ray photoelectron spectroscopy (XPS). Commercially available indium tin oxide (ITO) and ITO/SnO2 were used as substrates. The CdS layers were deposited in vacuum (~10−2Pa) at two different (low and high) substrate temperatures by close spaced sublimation technique. During the growth of CdS layer, the substrate temperature was increased from 25 to 250°C for low temperature layer and from 490 to 550°C for high temperature CdS layer due to the high crucible temperature. Similar to CdTe solar cell device process steps, the samples (TCO/CdS) were annealed in vacuum (10−2Pa) at 520°C and in air at 375°C with and without CdCl2. The XPS depth profile analysis shows that annealing ITO/CdS sample in vacuum induces diffusion of indium into the CdS layer from ITO. The most of the diffused indium atoms are found on top of the CdS layer. No indium diffusion into the CdS layer was observed for the TCO with SnO2 buffer layer between ITO and CdS. However, at SnO2/CdS interface Cd atoms diffuse into the SnO2 buffer layer after CdCl2 activation. The change in chemical and electronic properties of the ITO/CdS and ITO/SnO2/CdS interfaces is discussed in detail.

Indium Diffusion and Native Oxide Removal during the Atomic Layer Deposition (ALD) of TiO2 Films on InAs(100) Surfaces

A thermal atomic layer deposition (ALD) process with tetrakis(dimethylamino) titanium and H2O as reagents has been used to deposit TiO2 films on native oxide and etched InAs(100) surfaces at 200 °C. TiO2 was deposited on etched InAs(100) surface without the formation of undesirable interfacial layers. X-ray photoelectron spectroscopy (XPS) data on a series of films of increasing thickness deposited on surfaces covered with native oxide has shown that the surface arsenic oxides are removed within the first 2-3 nm of film deposition. The indium oxides, however, after an initial reduction seem to persist and increase in intensity with film thickness. For a 6.4-nm-thick TiO2 film, XPS depth profile data demonstrate an accumulation of indium oxides at the TiO2 film surface. When the topmost layer of the indium/TiO2 film is removed, then a sharp interface between the TiO2 film and the InAs substrate is detected. This observation demonstrates that the surface oxides diffuse through fairly thick TiO2 films and may subsequently be removed by reaction with the precursor and amine byproducts of the ALD reaction. These findings underscore the importance of diffusion in understanding the so-called "interface clean-up" reaction and its potential impact on the fabrication of high-quality InAs and other Group III-V-based MOS devices.

Indium diffusion through high-k dielectrics in high-k/InP stacks

Evidence of indium diffusion through high-k dielectric (Al2O3 and HfO2) films grown on InP (100) by atomic layer deposition is observed by angle resolved X-ray photoelectron spectroscopy and low energy ion scattering spectroscopy. The analysis establishes that In-out diffusion occurs and results in the formation of a POx rich interface.

Indium outdiffusion and leakage degradation in metal/Al2O3/In0.53Ga0.47As capacitors

Annealing of Ni/Al2O3/InGaAs structures results in a significant increase of the leakage current. The same treatment of Au/Ti/Al2O3/InGaAs structures results in a slight increase in leakage only. Time of flight secondary ions mass spectrometry measurements detected an annealing induced indium outdiffusion into the dielectric layer. In structures having nickel metallization, the released indium accumulated at the Ni/Al2O3 interface. In structures having Au/Ti metallization, the indium atoms penetrated into the gold layer, and an indium free Al2O3 layer was observed. We attribute the observed different electrical behavior to the different indium diffusion behavior, and eliminate other explanations.

Investigation of thermal interdiffusion in InAs/In0.15Ga0.85As/GaAs quantum dot-in-a-well heterostructures

An analysis of the effects of rapid thermal annealing on the photoluminescence spectrum of InAs/In0.15Ga0.85As/GaAs Quantum dot-in-a-well heterostructures is presented. The variation of ground state interband transition energies with annealing has been modeled and the effect of varying dot aspect ratios, well indium concentrations and well thicknesses analysed on both peak transition energy and interdiffusion driven blueshift in the photoluminescence spectrum. Our simulations indicate that at low annealing temperatures indium diffusion from InAs dot to InGaAs well dominates, while at higher temperatures indium diffusion from well to GaAs barrier is predominant. Further, we see an increase in strain relaxation as the coverage of dots with InGaAs is increased, and as the indium concentration and/or thickness of InGaAs well is increased. Our model is useful in engineering dot-in-a-well heterostructures with the dual aim of achieving a desired peak wavelength and minimizing blueshift due to annealing.

AlGaN/GaN/InGaN/GaN DH-HEMTs with GaN channel layer grown at high temperature

The AlGaN/GaN/InGaN/GaN double heterojunction high electron mobility transistors (DH-HEMTs) sample has been grown by MOCVD on (0 0 0 1) sapphire substrate. The structure features a 7 nm In 0.046 Ga 0.954 N interlayer determined by Rutherford backscattering (RBS). Since the polarization field in the InGaN interlayer is opposite to it in the AlGaN layer, an additional potential barrier is introduced between the two-dimensional electron gas (2DEG) channel and buffer, leading to enhanced carrier confinement and improved buffer isolation. The GaN layers between the AlGaN layer and InGaN interlayer are divided into two layers consisting of GaN channel layer which provides high mobility 2DEG grown at 1070 °C and GaN spacer layer grown at the same temperature as InGaN interlayer (800 °C) to prevent indium diffusion. RBS measurement confirms that the 3 nm GaN spacer layer isolates the InGaN interlayer well and free from diffusion. Hall measurement has been performed, the mobility as high as 1552 cm 2 /V s at room temperature is obtained and the sheet carrier density is 1.55 × 10 13 cm −2 . The average sheet resistance is 331 Ω/sq, respectively. The mobility obtained in this paper is about 20% higher than similar structures reported.

Diffusion Kinetics of Indium in TiO2 (Rutile)

This work determines the self‐diffusion coefficients of indium in TiO2 single crystal (rutile). Diffusion concentration profiles were imposed by deposition of a thin surface layer of InCl3 on the TiO2 single crystal and subsequent annealing in the temperature range 1073–1573 K. The diffusion‐induced concentration profiles of indium as a function of depth were determined using secondary ion mass spectrometry (SIMS). These diffusion profiles were used to calculate the self‐diffusion coefficients of indium in the polycrystalline In2TiO5 surface layer and the TiO2 single crystal. The temperature dependence of the respective diffusion coefficients, in the range 1073–1573 K, can be expressed by the following formulas: urn:x-wiley:00027820:media:jace12244:jace12244-math-0001and urn:x-wiley:00027820:media:jace12244:jace12244-math-0002The obtained activation energy for bulk diffusion of indium in rutile (316 kJ/mol) is similar to that of zirconium in rutile (325 kJ/mol). The determined diffusion data can be used in selection of optimal processing conditions for TiO2–In2O3 solid solutions.

Interfacial reactions in In/Cu2Se couples

In/Cu2Se couples were reacted at 623K and 723K for 1800–14,400s. In4Se3 and non-planar finger-type CuInSe2 were formed at the In/Cu2Se interface. The η-Cu2In phase was formed with longer reaction time. In addition to these phases formed at the interfaces, precipitates of CuInSe2 formed in the Cu2Se substrate and chunky CuInSe2 phase formed at the end of the Cu2Se substrate. Results in the In/Cu2Se/Ni couple reacted at 723K show that the reaction phases at the In/Cu2Se interface and the CuInSe2 precipitates in the Cu2Se substrate are the same, but there is no chunky CuInSe2 phase at the Cu2Se end adjacent to Ni. The CuInSe2 precipitates in the Cu2Se substrate are formed due to supersaturation of indium caused by a decrease in solubility at lower temperatures. The non-planar morphology of the CuInSe2 phase at the interface is caused by the fast diffusion of indium, the segregation and preferred facet growth of the CuInSe2 phase. However, the mechanism for the formation of the chunky CuInSe2 is not clear and further study is required.

Marked improvement in the stability of small molecule organic photovoltaics by interfacial modification using self-assembled monolayers to prevent indium diffusion into the active layer

This work describes a simple process to improve the stability of small molecule organic photovoltaics (OPVs) that use poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the hole transport layer (HTL), without reducing the power conversion efficiency (PCE). We investigated the effect of self-assembled monolayers (SAMs) on the degradation of electrical properties caused by the diffusion of indium through the matrix commonly used in OPV devices. X-ray photoelectron spectroscopy depth profiles suggested that the acidic PEDOT:PSS etched the indium from the indium tin oxide (ITO) electrode, which resulted in indium diffusion into and chemical interaction with the active layer. Such behavior was responsible for the deterioration of the device. By inserting a self-assembled monolayer (SAM) with carboxylic acid functional groups at the interface between the ITO and PEDOT:PSS layers, such diffusion could be significantly suppressed. The PCE of the pristine OPV diminished to zero at 49 days post-fabrication under ambient conditions. However, the PCE of the SAM-modified device was reduced by only 30% over the same period, and only to 48% after 98 days. Moreover, the SAMs improved the interfacial electrical properties between the ITO and PEDOT:PSS layers, which maintained the PCE of the device. Our findings suggest a simple approach to improve the stability of OPVs that utilize PEDOT:PSS as the HTL.

Plasmonic organic photovoltaic devices with graphene based buffer layers for stability and efficiency enhancement

Enhancement of photoconversion efficiency (PCE) and stability in bulk heterojunction (BHJ) plasmonic organic photovoltaic devices (OPVs) incorporating graphene oxide (GO) thin films as the hole transport layer (HTL) and surfactant free Au nanoparticles (NPs) between the GO HTL and the photoactive layers is demonstrated. In particular the plasmonic GO-based devices exhibited a performance enhancement by 30% compared to the devices using the traditional PEDOT:PSS layer. Likewise, they preserved 50% of their initial PCE after 45 h of continuous illumination, contrary to the PEDOT:PSS-based ones that die after 20 h. The performance increase is attributed to the improved photocurrent and fill factor owing to the enhanced exciton generation rate due to NP-induced plasmon absorption enhancement. Besides this, the stability enhancement can be attributed to limited oxygen and/or indium diffusion from the indium tin oxide (ITO) electrode into the active layer. The industrial exploitation of composite GO/NPs as efficient buffer layers in OPVs is envisaged.

Improving the lifetime of a polymer light-emitting diode by introducing solution processed tungsten-oxide

We report a polymer light-emitting diode (PLED) using solution processed tungsten-oxides (WOx). Coating of a thin WOx layer on PEDOT:PSS increases the current efficiency of PLED from 9.11 to 9.90 cd A−1 because of the improved conductivity of the PEDOT:PSS due to the incorporation of WOx. Improvement of the conductivity of PEDOT:PSS promotes hole injection into the emission layer. The lifetime of a PLED with WOx layers on both sides of PEDOT:PSS is 1.8 × 106 h which is around 20 times longer than that of the control device at 1000 cd m−2. The enhanced lifetime is due to the suppression of the indium diffusion from ITO to PEDOT:PSS by WOx and also due to the prevention of acidic damage that can occur to ITO and the organic emission layer by sulfate ions in PEDOT:PSS.

Controlled electroluminescence of n-ZnMgO/p-GaN light-emitting diodes

Effective control of room-temperature electroluminescence of n-ZnMgO/p-GaN light-emitting diodes (LEDs) over both emission intensity and wavelength is demonstrated. With varied Mg concentration, the intensity of LEDs in the near-ultraviolet region is increased due to the effective radiative recombination in the ZnMgO layer. Furthermore, the emission wavelength is shifted to the green/yellow spectral region by employing an indium-tin-oxide thin film as the dopant source, where thermally activated indium diffusion creates extra deep defect levels for carrier recombination. These results clearly demonstrate the effectiveness of controlled metal incorporation in achieving high energy efficiency and spectral tunability of the n-ZnMgO/p-GaN LED devices.

Modification of the optoelectronic properties of sprayed In2S3 thin films by indium diffusion for application as buffer layer in CZTS based solar cell

In this report the authors discuss the effect of diffusion of metallic indium on the optoelectronic properties of chemical spray deposited indium sulfide (In2S3) thin films which are prospective candidates for buffer layer application in thin film solar cells. Thin layers of metallic indium having different thicknesses were diffused into the films by evaporating different quantities of indium using vacuum evaporation technique followed by annealing. ‘In’ diffusion was done with an aim to reduce resistivity and improve the crystallinity to ensure better carrier collection. X-ray diffraction, X-ray photoelectron spectroscopy, optical absorption, photoluminescence and electrical studies were performed on the films. Analysis indicated that crystallinity attained a maximum for an optimum ‘In’ diffusion and then showed a retracing nature. Resistivity was found to decrease drastically from 2.3×105Ωcm [pristine] to 4.7Ωcm [for the optimum indium diffused samples]. Using the optimized In2S3 layer and copper zinc tin sulfide (CZTS) deposited using chemical spray pyrolysis, a heterojunction device was successfully fabricated with a conversion efficiency of 1.85% and fill factor of 52%. The optimum quantity of indium to be diffused depends on the thickness of the In2S3 thin film.

Diffusion of indium atoms into iridium through an intermediate graphite monolayer

Peculiar features of diffusion of indium atoms into iridium through a graphite monolayer have been revealed for the first time by thermodesorption spectroscopy. The most intense diffusion of indium into iridium has occurred in the Ir(111)-C[plain] system at 1400 K < T < 1600 K. The fractions of the fluxes of intercalation \(\bar \delta = 0.3 \pm 0.05\) and diffusion δIn = Ndif/N = 2 × 10−3 indium atoms in the Ir(111)-C system have been found. It has been demonstrated that the amount of intercalated and diffused indium depends on the electrical field, i.e., on the positive potential in the Ir(111)-C system. A noticeable diffusion of indium into iridium started at 200 V and increased up to 2500 V. The activation energies for indium diffusion into and from iridium have been determined to be En1 = 5.05 ± 0.05 eV and En1 = 5.4 ± 0.1 eV, respectively.

Influence of laser lift-off on optical and structural properties of InGaN/GaN vertical blue light emitting diodes

The influences of the laser lift-off (LLO) process on the InGaN/GaN blue light emitting diode (LED) structures, grown on sapphire substrates by low-pressure metalorganic chemical vapor deposition, have been comprehensively investigated. The vertical LED structures on Cu carriers are fabricated using electroplating, LLO, and inductively coupled plasma etching processes sequentially. A detailed study is performed on the variation of defect concentration and optical properties, before and after the LLO process, employing high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) observations, cathodoluminescence (CL), photoluminescence (PL), and high-resolution X-ray diffraction (HRXRD) measurements. The SEM observations on the distribution of dislocations after the LLO show well that even the GaN layer near to the multiple quantum wells (MQWs) is damaged. The CL measurements reveal that the peak energy of the InGaN/GaN MQW emission exhibits a blue-shift after the LLO process in addition to a reduced intensity. These behaviors are attributed to a diffusion of indium through the defects created by the LLO and creation of non-radiative recombination centers. The observed phenomena thus suggest that the MQWs, the active region of the InGaN/GaN light emitting diodes, may be damaged by the LLO process when thickness of the GaN layer below the MQW is made to be 5 μm, a conventional thickness. The CL images on the boundary between the KrF irradiated and non-irradiated regions suggest that the propagation of the KrF laser beam and an accompanied recombination enhanced defect reaction, rather than the propagation of a thermal shock wave, are the main origin of the damage effects of the LLO process on the InGaN/GaN MQWs and the n-GaN layer as well.

Suppressed indium diffusion and enhanced absorption in InGaAs/GaAsP stepped quantum well solar cell

A multiple stepped quantum well (MSQW) structure, in which GaAs step layers are sandwiched between strain-balanced InGaAs wells and GaAsP barriers, has been proposed and improvements in sub-GaAs-bandgap QE have been demonstrated. We have studied the effect of indium diffusion on the optical properties in quantum well solar cell by measuring the absorptance and photoluminescence spectra. Theoretical calculations indicate that the transition energy level and the absorption magnitude are sensitive to indium diffusion. The MSQW structure with GaAs step layer is a feasible way to suppress indium diffusion and enhance the absorption.

Long-lasting flexible organic solar cells stored and tested entirely in air

We report on improved stability of poly(3-hexylthiopene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester bulk heterojunction solar cells using an indium tin oxide (ITO) anode and an indium metal cathode. Except for the ITO anode the devices are fabricated, stored, and tested entirely in air without encapsulation, exhibiting less than 10% loss in power conversion efficiency after 200 days. X-ray photoelectron spectroscopy shows that this improvement in ambient stability is correlated with the diffusion of indium from the cathode into the active polymer. The In oxidizes presumably resulting in a reduction in P3HT polymer chain degradation.

Indium incorporation in InGaN/GaN quantum wells grown on m‐plane GaN substrate and c‐plane sapphire

AbstractInGaN/GaN quantum wells (QWs) grown at identical conditions on m‐plane GaN and c‐plane sapphire substrates were characterized by several techniques, aiming to clarify the reason for different emission wavelengths often observed in similar LED structures with m‐ and c‐plane surface orientations. Cathodoluminescence (CL) spectra of m‐plane QWs revealed shorter wavelength and no blueshift with increasing CL probe current in accordance with previous reports. Relative indium compositions were estimated by high‐resolution X‐ray diffraction to be 5.1 and 13.9% for m‐plane and c‐plane QWs, respectively. Cross‐sectional transmission electron microscopy images revealed that the well widths of the m‐plane QWs were noticeably thicker than those of the c‐plane QWs. The lower indium compositions and thicker well widths of the m‐plane QWs indicated that different indium incorporation and diffusion occurred in the structures grown on the GaN substrate, which is attributed to its surface off‐cut toward [0001] and the higher thermal conductivity with respect to that of sapphire.

Reactivity between In2O3 and TiO2 (rutile) studied using secondary ion mass spectrometry (SIMS)

The present work considers the reaction kinetics between titanium dioxide, TiO2 (rutile) single crystal and a thin layer of indium oxide, In2O3 deposited on its surface. The reported experimental data are reflective of the chemical reaction involving the diffusive transport of In3+ in the rutile phase. The reaction progress at 1173K is monitored using the secondary ion mass spectrometry (SIMS) technique. It is shown that the SIMS depth profiles may be considered in terms of two distinctly different components, related to the surface layer of In2O3, and the rutile single crystal phase beneath. The depth profile of the rutile phase involves the region related to bulk diffusion of indium as well as the background composition. The bulk diffusion coefficient of indium, In3+ in single crystal TiO2 (rutile) at 1173K and p(O2)=21kPa was determined to be 4.4(±0.2)×10−18m2s−1.