Interfacial Oxide Layer Research Articles

Low-Temperature Bonding of Nanolayered InGaP/SiO2 Waveguides for Spontaneous-Parametric Down Conversion

The integration of III–V materials on photonic integrated circuits has enjoyed a lot of attention because of the necessity of merging photon sources with silicon electronics. Nevertheless, III–V source integration technologies are not sufficiently mature, inhibiting the employment of such platforms to a broader range of applications. Here, we present a novel approach that enables the transfer of III–V nanolayers (≈250 nm) to silicates via oxide bonding. Through use of a thick photoresist scaffold (≈30 μm), complete removal of the substrate can be performed while preserving the relative structure morphology. The use of the III–V native oxide without depositing interfacial oxide layers greatly reduces the processing time and cost. The transfer of an array composed of 1 mm long InGaP waveguides with 250 nm thickness and widths spanning from 0.7 to 11.2 μm to a SiO2 substrate has been experimentally demonstrated, evidencing the feasibility of the technique for wafer-scale processing. The application of the nanolayered waveguides in the spontaneous-parametric down-conversion process has been tested by photon-correlation measurement, showing good agreement with the theoretical model.

High-temperature internal oxidation behavior of surface cracks in low alloy steel bloom

The oxidation behavior and mechanism near the crack of bloom was investigated by prefabricated crack and oxidation at high temperature (1000 – 1200 °C). The interface oxide layer composed of Fe2SiO4 and FeCr2O4 can prevent the steel matrix from being oxidized. However, the melting point of Fe2SiO4 is approximately 1170 °C, so the interface oxide layer is in a metastable state with the progress of high-temperature oxidation. At this time, the thickness of the internal oxidation spot layer in the steel matrix increases rapidly. As a result, internal oxidation mechanism of surface cracks at high temperature is clarified.

Surface reaction dependence of molecular beam epitaxy grown aluminum on various orientations of β-Ga2O3

An orientational dependence on the interfacial reaction between aluminum and (010), (001), and (2̄01) β-Ga2O3 substrates is addressed. Electron microscopy and x-ray diffraction were used to assess the interface crystallinity, thickness, and chemical composition of the interfacial layers. At the interface, amorphous aluminum oxide is observed in all three samples with a thicknesses of 3.5 nm for (010) β-Ga2O3 and 2 nm for (001) β-Ga2O3 and (2̄01) β-Ga2O3. Aluminum oxide is formed at the interface as a result of a chemical reaction that reduces the Ga2O3 surface when aluminum is deposited. We propose that in Al on (010) β-Ga2O3, in which the thickest interfacial oxide layer is observed, diffusional pathways of consecutive octahedral Ga sites perpendicular to the interface promote increased interdiffusion in the out-of-plane direction. In contrast, the (001) β-Ga2O3 and (2̄01) β-Ga2O3 substrates exhibit alternating rows of tetrahedral and octahedral Ga sites parallel to the interface, where the rows of tetrahedral Ga sites act as increased energy barriers that impede interdiffusion of Al and β-Ga2O3. The orientational dependence of metal-oxide interlayers in β-Ga2O3 can impact electronic and thermal transport, pointing to the importance of understanding the impact of β-Ga2O3 orientation on interfacial properties.

Enhanced Ductility by Controlling Thickness of Interfacial Oxide Layer in B4c/Al Composites

Enhanced Ductility by Controlling Thickness of Interfacial Oxide Layer in B4c/Al Composites

Effects of interfacial oxide layer formed by annealing process on WORM characteristics of Ag/CuxO/SiOx/n+–Si devices

In this paper, we investigate the effects of a SiOx interfacial layer on ON/OFF current ratios, endurance characteristics and read-disturb immunities of Ag/CuxO/SiOx/n+-Si write-once-read-many-times (WORM) memories. The CuxO active layers were prepared using a sol-gel process. After coating CuxO films on n+-Si substrates, the CuxO/n+-Si samples were annealed in air at 400 ℃ and 600 ℃, respectively, to obtain a SiOx interfacial layer at the CuxO/n + -Si interfaces. The 400 ℃-annealed CuxO device shows an ON/OFF current ratio of 104. However, degradation of OFF state current (IOFF) with increasing read-pulse cycles and stress time is observed. For the 600 ℃-annealed CuxO device, stable ON and OFF state currents can be observed both in an endurance test for over 1.2 × 104 read cycles and in a read-disturb test for 2 × 104 s. Moreover, a higher ON/OFF current ratio of 107 is obtained. A rigorous retention test executed at an elevated temperature of 85 ℃ indicates that the data retention time is expected to last for 10 years. The performance improvement of the 600 ℃-annealed CuxO device is due to an increase in the thickness of the SiOx interfacial oxide layer. The mechanism for the influence of the interfacial layer on memory performance is investigated and illustrated. The OFF state current of the memory is limited by hopping and trap-assisted tunneling transport in the SiOx interfacial layer. In the ON state, conductive paths in the device cause that the carriers can easily migrate by Ohmic and space charge limited conduction.

Progress with passivation and screen-printed metallization of Boron-doped monoPoly™ layers

In this work we have analyzed the doping, passivation and contact properties of boron-doped (p+) polysilicon (poly-Si) layers to understand the two key limiting factors for industrial adoption of p+ poly-Si based passivated contacts: challenges with diffusion and challenges with screen-printed, fire-through (FT) metallization. Investigation of test samples with ex-situ doped poly-Si layers of varying thickness and surface morphologies revealed that sheet resistance (Rsheet) and passivation quality in ex-situ doped poly-Si are limited by the maximum solid solubility of boron in silicon, and possible damage to the interfacial silicon oxide (iOx) layer and increased Auger recombination at high diffusion temperatures, respectively. An interesting correlation is found between the maximum dopant density at the interface and the J0,pass, with the latter increasing with increasing dopant density. The contacts to p+ poly-Si layers are formed with commercially available FT Ag/Al pastes by screen printing process. Metal contact properties strongly depend on the surface morphology and thickness of poly-Si layer. Lower contact resistivity was achieved on textured surface with thickest poly-Si layers, while lowest recombination under metal contacts was achieved with planar surface with thickest poly-Si layer. Further microstructure analysis of metallized interfaces using Scanning electron microscope shows partial etching of thick (220 nm) poly-Si layers and near complete etching of thin (20 nm) poly-Si layers by FT Ag-Al pastes. Using optimized doping and contact conditions, excellent surface passivation in unmetallized regions (J0,pass of 3.8 fA/cm2), contact resistivities as low as 1.2 ± 0.8 mΩ-cm2 and recombination current densities under the metal contacts of 155 ± 10 fA/cm2 are achieved on textured and planar samples respectively.

Role of transferred graphene on atomic interaction of GaAs for remote epitaxy

Remote epitaxy is a recently discovered type of epitaxy, wherein single-crystalline thin films can be grown on graphene-coated substrates following the crystallinity of the substrate via remote interaction through graphene. Although remote epitaxy provides a pathway to form freestanding membranes by controlled exfoliation of grown film at the graphene interface, implementing remote epitaxy is not straightforward because atomically precise control of interface is required. Here, we unveil the role of the graphene–substrate interface on the remote epitaxy of GaAs by investigating the interface at the atomic scale. By comparing remote epitaxy on wet-transferred and dry-transferred graphene, we show that interfacial oxide layer formed at the graphene–substrate interface hinders remote interaction through graphene when wet-transferred graphene is employed, which is confirmed by an increase of interatomic distance through graphene and also by the formation of polycrystalline films on graphene. On the other hand, when dry-transferred graphene is employed, the interface is free of native oxide, and single-crystalline remote epitaxial films are formed on graphene, with the interatomic distance between the epilayer and the substrate matching with the theoretically predicted value. The first atomic layer of the grown film on graphene is vertically aligned with the top layer of the substrate with these atoms having different polarities, substantiating the remote interaction of adatoms with the substrate through graphene. These results directly show the impact of interface properties formed by different graphene transfer methods on remote epitaxy.

Influence of Hybrid Sol-Gel Crosslinker on Self-Healing Properties for Multifunctional Coatings.

Self-healing polymers are a new class of material that has recently received a lot of attention because of the lifespan improvement it could bring to multiple applications. One of the major challenges is to obtain multifunctional materials which can self-heal and exhibit other interesting properties such as protection against corrosion. In this paper, the effect of the incorporation of an aminosilane on the properties of a self-healing organic polymer containing disulfide bond is studied on films and coatings for aluminium AA2024-T3 using simple one step in situ synthesis. Hybrid coatings with enhanced anticorrosion properties measured by EIS were obtained thanks to the formation of a protective oxide interface layer, while exhibiting wound closure after exposition at 75 °C. The thermal, mechanical and rheological properties of the films with different aminosilane amounts were characterized in order to understand the influence of the slight presence of the inorganic network. Stiffer and reprocessable hybrid films were obtained, capable to recover their mechanical properties after healing. The nanocomposite structure, confirmed by TEM, had a positive effect on the self-healing and stress relaxation properties. These results highlight the potential of sol-gel chemistry to obtain efficient anticorrosion and self-healing coatings.

Hybrid memory characteristics of NbOx threshold switching devices

By exploiting NbOx, we demonstrate its hybrid memory characteristics, indicating that resistive switching is unified with selector behavior. First, we identify that the 50-nm-thick amorphous NbOx inherently shows volatile threshold switching (TS). To enable memory switching (MS) in NbOx, device environments are configured that can supply oxygen vacancies or cations constituting a conductive filament (CF). In the Al/NbOx/TiN stack, oxygen vacancies can be internally generated from an interfacial oxide layer formed by the chemical reaction between a highly reactive Al electrode and NbOx, which is confirmed via multiple physical analyses. When the effect of the extrinsic vacancies becomes comparable to the intrinsic properties of the NbOx, the hybrid memory characteristics are observed. While the TS prevents leakage current, the MS is driven by oxygen vacancy CF, allowing multilevel cell operation. Furthermore, hybrid switching can be obtained using the Cu/NbOx/TiN stack. However, the effect of a Cu CF is dominant, because the Cu electrode can externally provide ions infinitely in this case; therefore, hybrid memory behavior is achieved after MS is performed.

Micro-photoluminescence studies of shallow boron diffusions below polysilicon passivating contacts

Micro-photoluminescence is utilised in this work to study the shallow boron diffusions that occur underneath p + polysilicon passivating contacts. Regions with high boron concentrations emit a photoluminescence peak at a higher wavelength compared to the substrate crystalline silicon due to band-gap narrowing. We demonstrate the presence of this peak with samples following optimised fabrication procedures based on previous studies for thermally BBr3 diffused polysilicon passivating contacts. The intensities of the diffusion peaks, when normalised against the substrate crystalline silicon peak, change with the dopant concentration profiles, which in turn vary with the BBr3 diffusion temperatures as well as the thickness of the interfacial oxide layer. Comparisons are made between the photoluminescence spectra from p + polysilicon passivating contacts and n + polysilicon contacts reported previously [1]. We find that the sub-band-gap photoluminescence peaks arising from the n + polysilicon layers themselves are absent in the p + polysilicon contacts. This simplifies the procedure for photoluminescence spectra measurements in the case of p + polysilicon contacts. Further demonstration of micron-scale spectral photoluminescence mapping with localised p + polysilicon structures demonstrates the feasibility of the method in detecting underlying boron diffused regions with a spatial resolution of below 10 μm. Such micron-scale mapping will be useful for characterising localised polysilicon structures, such as polysilicon under the fingers on the front side of solar cells, or in interdigitated back contact devices.

Influence of Polysilicon Thickness on Properties of Screen‐Printed Silver Paste Metallized Silicon Oxide/Polysilicon Passivated Contacts

This work investigates how the thickness of the polysilicon layer and temperatures during contact sintering influence the properties of SiOx/polysilicon passivated contacts. The n+ polysilicon layers deposited by low‐pressure chemical vapor deposition (LPCVD) on top of a thin wet chemically grown interface oxide layer providing chemical and field‐effect passivation on n‐type monocrystalline silicon wafers are investigated. Three different polysilicon layer thicknesses of 50, 100, and 150 nm are considered in this work. A high level of passivation with implied Voc values above 735 mV and J01 below 5 fA cm−2 is obtained for symmetric lifetime test samples. These samples are used to investigate the interaction of the silver paste with the polysilicon layer at different fast firing peak temperatures. Reduction in polysilicon layer thickness leads to an increase in contact resistivity as well as in J0met. Excellent J0met values of the order of J01 with contact resistivity values below 2 mΩ cm2 are obtained for samples with polysilicon layers of 100 and 150 nm thickness.

Examination of the Oxidation and Metal–Oxide Layer Interface of a Cr–Nb–Ta–V–W High Entropy Alloy at Elevated Temperatures

As the aerospace industry continues to grow, so does the demand for materials to withstand extreme environments. Refractory high entropy alloys (HEA) that utilize refractory elements are a rising class of materials with tremendous potential for use in these applications. Chintalapalle V. Ramana, and co-workers examine in their article, number 2100164, the oxidation behavior of a novel refractory HEA at different temperatures and highlight the differences.

Electrical and optical properties of (Ta2O5)1−x–(TiO2)x films, x = 0.035, prepared by sputtering of ceramic and mosaic (Ta, Ti) metal targets

(Ta2O5)1−x–(TiO2)x, with x = 0.035, thin films were deposited onto p-type silicon and quartz substrates following two different routes: first, by the sputtering of the ceramic target and, second, by sputtering of mosaic (Ta, Ti) metal target in the presence of oxygen (hereafter referred to as CT and MT, respectively). The deposited films were found to crystallize on annealing at and above 700 °C. The dielectric constant of the prepared films was found to increase with increasing annealing temperature, up to 700 °C, and on annealing at 800 °C, it was found to decrease. The dielectric constant of the CT was observed to be higher than that of the MT film structures at each annealing temperature. From the transmittance measurements, different optical parameters of the deposited crystalline films were calculated. The leakage current density of the CT films was found to increase with the annealing temperature, whereas in the MT films, it drastically decreased by an order of ∼3 when the annealing temperature was increased from 700 to 800 °C. Different conduction mechanisms were observed in the different applied field regions in the prepared film structure. The observed electrical properties of the prepared film structure seem to depend on the status of the growing interfacial oxide layer on annealing.

Coupled Investigation of Contact Potential and Microstructure Evolution of Ultra-Thin AlOx for Crystalline Si Passivation.

In this work, we report the same trends for the contact potential difference measured by Kelvin probe force microscopy and the effective carrier lifetime on crystalline silicon (c-Si) wafers passivated by AlOx layers of different thicknesses and submitted to annealing under various conditions. The changes in contact potential difference values and in the effective carrier lifetimes of the wafers are discussed in view of structural changes of the c-Si/SiO2/AlOx interface thanks to high resolution transmission electron microscopy. Indeed, we observed the presence of a crystalline silicon oxide interfacial layer in as-deposited (200 °C) AlOx, and a phase transformation from crystalline to amorphous silicon oxide when they were annealed in vacuum at 300 °C.

Examination of the Oxidation and Metal–Oxide Layer Interface of a Cr–Nb–Ta–V–W High Entropy Alloy at Elevated Temperatures

The authors report on the evaluation of the oxide scale and the interface microstructure of a Cr–Nb–Ta–V–W refractory high entropy alloy (HEA) at elevated temperatures. The Cr–Nb–Ta–V–W HEA is oxidized at 700 and 800 °C in lab air and the substrate/oxide interface is investigated. Combined in situ X‐ray diffraction (XRD) coupled with ex situ scanning electron microscopy (SEM) and energy dispersive X‐ray spectrometry (EDS) analyses characterize the oxide scale and confirm the phases present in the substrate which have been previously identified in this alloy. The microstructure near the interface is studied for an indication of selective oxidation of this alloy. Cracking and porosity are found along the interface layer which grows directionally outward. Two main oxides are identified: a W‐based oxide with a needle‐like structure and a Cr oxide containing Ta that has a granular structure, primarily found in clusters. The oxide layers are porous, and no dense protective oxide is identified. It is found that when the temperature is increased to 800 °C, the oxide layer exhibits an increase in thickness. In situ XRD indicates that V is the first element to oxidize.

Role of Interfacial Oxide Layer in MoOx/n-Si Heterojunction Solar Cells

Interfacial oxide layer plays a crucial role in a MoOx/ n -Si heterojunction (MSHJ) solar cell; however, the nature of this interfacial layer is not yet clarified. In this study, based on the experimental results, we theoretically analyzed the role of the interfacial oxide layer in the charge carrier transport of the MSHJ device. The interfacial oxide layer is regarded as two layers: a quasi p -type semiconductor interfacial oxide layer (SiOx(Mo))1 in which numerous negatively charged centers existed due to oxygen vacancies and molybdenum–ion-correlated ternary hybrids and a buffer layer (SiOx(Mo))2 in which the quantity of Si-O bonds was dominated by relatively good passivation. The thickness of (SiOx(Mo))1 and the thickness of (SiOx(Mo))2 were about 2.0 nm and 1.5 nm, respectively. The simulation results revealed that the quasi p -type layer behaved as a semiconductor material with a wide band gap of 2.30 eV, facilitating the transport of holes for negatively charged centers. Additionally, the buffer layer with an optical band gap of 1.90 eV played a crucial role in passivation in the MoOx/ n -Si devices. Furthermore, the negative charge centers in the interfacial layer had dual functions in both the field passivation and the tunneling processes. Combined with the experimental results, our model clarifies the interfacial physics and the mechanism of carrier transport for an MSHJ solar cell and provides an effective way to the high efficiency of MSHJ solar cells.

High‐Performance Polymer Photodetectors using ZnO Nanocrystal Trap States

A metal oxide interfacial layer is introduced into polymer photodetectors (PPDs) to achieve low dark current and high photocurrent. Although the defects of the metal oxide play a key role in device operation, defect effects on PPDs are poorly understood. Herein, PPDs using nanoparticle (NP) and amorphous zinc oxide (ZnO) films as the indium tin oxide (ITO) modification layer are realized and characterized, and the former device shows high performance in every figure of merit: external quantum efficiency of 1980%, detectivity of 1.03×1014 Jones, responsivity of 9.51 A W−1, response time of ≈10 μs, and linear dynamic range of over 100 dB at a low reverse bias. The comparison of the NP ZnO and amorphous ZnO‐based devices and the ultraviolet (UV) light illumination effect on the devices imply the underlying operation mechanism. The surface defects in the ZnO NPs efficiently block external charge injection, whereas the defect‐induced photogenerated charge accumulation at the interface between the ZnO layer and the active layer leads to a tunneling current under illumination. This methodology provides universal guidance for fabricating high‐performance PPDs based on a metal oxide interfacial layer.

Effect of various PCBM doping on the interfacial layer of Al/PCBM:ZnO/p-Si photodiodes

The light can be detected by various devices such as photoconductors, photodetectors, phototransistors, solar cells, and photodiodes, and the light can be employed energy harvesting as well as sensing applications. Various materials can be utilized to raising of the efficiency of light-based devices. In this present study, metal–semiconductor (MS) devices with various [6,6]-Phenyl C61-butyric acid methyl ester (PCBM)-doped zinc oxide (ZnO) interfacial layer were fabricated for photodiode applications. Commercially purchased PCBM and ZnO were mixed in order to obtain undoped, 3%, 5%, and 10% PCBM-doped ZnO interfacial layer for Al/PCBM:ZnO/p-Si devices. The obtained solutions were layered on the p-type silicon (p-Si) substrates by spin-coating method. The thermal evaporation technique was utilized to deposit Al metal electrodes both back and front sides. The morphological properties of the fabricated devices were characterized by AFM. The morphological images of the AFM revealed that PCBM doping affected the surface morphology as well as surface roughness of the ZnO layers. I–V measurements were carried out in the dark and under varying illumination conditions for electrical properties. The devices exhibited good rectifying properties at around 103 rates, both dark and various illumination conditions, according to I–V graphs. The junction parameters of the produced devices were determined by using thermionic emission, Norde, and Cheung models from the I–V characteristics of the devices. The devices have high ideality factors, and these values generally fluctuate with varying PCBM-doping amounts. The current transient measurements show that PCBM doping provide increasing in the light response capacity. According to the results, the devices can be employed as photodiode and photodetector applications for the further works in the industry.

Hysteresis-Free Negative Capacitance Effect in Metal-Ferroelectric-Insulator-Metal Capacitors with Dielectric Leakage and Interfacial Trapped Charges

The negative capacitance (NC) stabilization of a ferroelectric (FE) material can potentially provide an alternative way to further reduce the power consumption in ultra-scaled devices and thus has been of great interest in technology and science in the past decade. In this article, we present a physical picture for a better understanding of the hysteresis-free charge boost effect observed experimentally in metal-ferroelectric-insulator-metal (MFIM) capacitors. By introducing the dielectric (DE) leakage and interfacial trapped charges, our simulations of the hysteresis loops are in a strong agreement with the experimental measurements, suggesting the existence of an interfacial oxide layer at the FE-metal interface in metal-ferroelectric-metal (MFM) capacitors. Based on the pulse switching measurements, we find that the charge enhancement and hysteresis are dominated by the FE domain viscosity and DE leakage, respectively. Our simulation results show that the underlying mechanisms for the observed hysteresis-free charge enhancement in MFIM may be physically different from the alleged NC stabilization and capacitance matching. Moreover, the link between Merz's law and the phenomenological kinetic coefficient is discussed, and the possible cause of the residual charges observed after pulse switching is explained by the trapped charge dynamics at the FE-DE interface. The physical interpretation presented in this work can provide important insights into the NC effect in MFIM capacitors and future studies of low-power logic devices.

Fabrication of ZnO interface layer from a novel aqueous sol-gel precursor solution for organic solar cells

To improve the morphology and charge transport property of zinc oxide (ZnO) interface layer in the field of organic solar cells (OSCs), a novel ZnO sol-gel precursor was developed by redox reaction among zinc powder (Zn), hydrogen peroxide (H2O2), and ammonia (NH3·H2O) in aqueous solvent. This aqueous ZnO sol-gel precursor has advantages in cost and stability. Furthermore, photoelectric conversion performance of OSCs with ZnO layer (aqueous) is better than that of device with ZnO layer (nonaqueous). To further elaborate the relevance between the ZnO interface layer and the device performance, optical and morphology characteristics of precursor solutions, ZnO layers, and active layers were studied. Meanwhile, electrical characteristics of the OSCs were also analyzed. The results show less anion and larger colloidal particle size in aqueous sol-gel solution, which making the ZnO interface layer have fewer defects and larger surface roughness than nonaqueous-phase prepared ZnO layer. Thus, free electron could transfer from the active layer to ZnO layer more easily, and charge recombination is reduced at the interface. Moreover, the electron mobility of OSCs is also enhanced by the aqueous-phase prepared ZnO layer. Therefore, short-circuit current and photoelectric conversion performance of device are promoted.