Plasma-enhanced Atomic Layer Deposition Method Research Articles

Ga2O3@Al2O3 Core–Shell Nanowires for High-Performance Solar-Blind Photodetectors

High-performance solar-blind photodetectors (SBPDs) have been indispensable in both military and civilian applications. Herein, Ga2O3@Al2O3 core–shell nanowires (NWs) are synthesized by plasma-enhanced atomic layer deposition (PEALD) Al2O3 layer on the surface of Ga2O3 nanowires. The Ga2O3@Al2O3 NW has a length of tens of micrometers, and the thickness of Ga2O3 and Al2O3 layers in the NW is approximately 30 and 5 nm, respectively. The PEALD method passivates surface defects to improve the crystal quality of Ga2O3. The metal–semiconductor–metal (MSM) Ga2O3@Al2O3 NW-based SBPDs exhibit a superhigh sensitivity of 1.07 × 103 A/W and a high response speed of less than 83 ms at 5 V bias voltage under 254 nm irradiation. Additionally, the Ga2O3@Al2O3 NW PDs exhibit a superhigh specific detectivity of 3.38 × 1011 Jones, an external quantum efficiency (EQE) of 5.22 × 105%, and a high deep ultraviolet (DUV)/visible responsivity rejection ratio (R254/405) of 4.81 × 102. These results suggest that this method is an effective way to design and prepare high-performance photonic devices.

Atomic-Level Sn Doping Effect in Ga2O3 Films Using Plasma-Enhanced Atomic Layer Deposition

In this work, the atomic level doping of Sn into Ga2O3 films was successfully deposited by using a plasma-enhanced atomic layer deposition method. Here, we systematically studied the changes in the chemical state, microstructure evolution, optical properties, energy band alignment, and electrical properties for various configurations of the Sn-doped Ga2O3 films. The results indicated that all the films have high transparency with an average transmittance of above 90% over ultraviolet and visible light wavelengths. X-ray reflectivity and spectroscopic ellipsometry measurement indicated that the Sn doping level affects the density, refractive index, and extinction coefficient. In particular, the chemical microstructure and energy band structure for the Sn-doped Ga2O3 films were analyzed and discussed in detail. With an increase in the Sn content, the ratio of Sn-O bonding increases, but by contrast, the proportion of the oxygen vacancies decreases. The reduction in the oxygen vacancy content leads to an increase in the valence band maximum, but the energy bandgap decreases from 4.73 to 4.31 eV. Moreover, with the increase in Sn content, the breakdown mode transformed the hard breakdown into the soft breakdown. The C-V characteristics proved that the Sn-doped Ga2O3 films have large permittivity. These studies offer a foundation and a systematical analysis for assisting the design and application of Ga2O3 film-based transparent devices.

Ultrathin epitaxial NbNx film deposited by PEALD method on C-plane sapphire: Growth, structure and superconducting properties

Here we report on the results of obtaining and study of epitaxial ultrathin superconductive films of niobium nitride (NbNx) grown on a C-plane sapphire substrate. The films were deposited from the TBTDEN metal-organic precursor using the plasma-enhanced atomic layer deposition (PEALD) technique at 350 °C and NH3/Ar and H2/Ar gas mixtures as reactants. We employed X-ray diffraction (XRD), X-ray reflectometry (XRR), and high-resolution transmission electron microscopy (HRTEM) techniques to study the structural properties of the films. The investigation demonstrated that NbN layers grow in the plane (111) and consist of twins which axes 11¯0 are parallel to the substrate axes 11¯00 in the basal plane. The cubic lattice of layers is subject to rhombohedral deformation involving distortion of right angles up to 89° due to the four NbNx lattices coincide with the three sapphire lattices with misfit of 0.31%. We have also determined the quasiparticle diffusion constant and the coherence length of the NbNx films. The values of superconducting transition temperature and critical current density were determined as 12 K and 6.2 МА/cm2, respectively.

Large enhancement of photocatalytic activity in ZnO thin films grown by plasma-enhanced atomic layer deposition

In this work, we present a large, tenfold enhancement in the photocatalytic activity of thin ZnO films grown by plasma-enhanced atomic layer deposition (PE-ALD) at 100 °C, compared to values obtained for thin ZnO films deposited by a conventional thermal ALD method at the same temperature. Thus, we have demonstrated that we can deposit thin ZnO films using the PE-ALD method both at low temperatures and with a high photocatalytic ability. A number of structural (SEM, EDX, HRTEM, GIXRD, XRR, XPS, SIMS) and optical (UV-Vis, PL) experimental techniques have been employed to elucidate a possible physical origin of the observed remarkable difference in the photocatalytic activity of thin ZnO films grown by the PE-ALD method compared to those grown by the thermal ALD method.

Nanoscale Encapsulation of Perovskite Nanocrystal Luminescent Films via Plasma-Enhanced SiO2 Atomic Layer Deposition.

Photoluminescence perovskite nanocrystals (NCs) have shown significant potential in optoelectronic applications in view of their narrow band emission with high photoluminescence quantum yields and color tunability. The main obstacle for practical applications is to obtain high durability against an external environment. In this work, a low temperature (50 °C) plasma-enhanced atomic layer deposition (PE-ALD) protection strategy was developed to stabilize CsPbBr3 NCs. Silica was employed as the encapsulation layer because of its excellent light transmission performance and water corrosion resistance. The growth mechanism of inorganic SiO2 via PE-ALD was investigated in detail. The Si precursor bis(diethylamino)silane (BDEAS) reacted with the hydroxyl groups (-OH) and thereby initiated the subsequent silica growth while having minimal influence to the organic ligands and did not cause PL quenching. Subsequently, O2 plasma with high reactivity was used to oxidize the amine ligands of the BDEAS precursor while did not etch the NCs. The obtained CsPbBr3 NCs/SiO2 film exhibited exceptional stability in water, light, and heat as compared to the pristine NC film. Based on this method, a white light-emitting diode with improved operational stability was successfully fabricated, which exhibited a wide color gamut (∼126% of the National Television Standard Committee). Our work successfully demonstrates an efficient protection scheme via the PE-ALD method, which extends the applied range of other materials for stabilization of perovskite NCs through this approach.

Plasma enhanced atomic-layer-deposited nickel oxide on Co3O4 arrays as highly active electrocatalyst for oxygen evolution reaction

Energy storage technologies are developed over the past decades, such as metal-air batteries. The large-scale application of these devices is finite due to slow kinetics of the oxygen evolution reaction (OER). In order to solve this issue, plasma enhanced atomic layer deposition (PE-ALD) is used to synthesize high performance nano-oxide (NiOx@Co3O4/CC) electrocatalyst for OER applications. Herein, the cobalt oxide (Co3O4) nanowire arrays are grown on oxygen plasma-treated carbon-cloth (CC) and then a thin layer (~1.2 nm) of nickel oxide (NiOx) is deposited on the Co3O4/CC through PE-ALD method. The electrocatalyst of two transition metal oxides plays a leading role in improving the OER performance and stability. The overpotential for OER of NiOx@Co3O4/CC electrocatalyst is 360 mV at 10 mA cm−2, which is much lower than that of Co3O4/CC (420 mV) and comparable to commercial RuO2 (350 mV) electrocatalyst. Moreover, the stability of NiOx@Co3O4/CC electrocatalyst is also improved, which only 8.85% of the initial current is loss after 40,000 s. It is demonstrated that PE-ALD synthesis method provides a facile approach to fabricate highly efficient nano-oxide electrocatalysts for OER in energy storage devices.

Morphological and in situ local refractive index change induced tuning of the optical properties of titania coated porous gold nanoparticles

Porous nanoparticles are very popular because of their high surface/volume ratio; moreover, they have stronger plasmonic properties than their solid counterparts. Due to these properties, these are potential candidates in optical, or even in ophthalmological applications. We prepared porous gold nanoparticles on SiO2/Si as well as on sapphire substrates with solid-state dewetting–dealloying methods. In this work, we studied the morphological and optical properties of porous gold nanoparticles coated with a thin (∼7nm) TiO2 layer using the plasma-enhanced atomic layer deposition method. We show that heat treatments can be used to tune the optical properties of titania coated porous gold hybrid nanoparticles in a wide range of wavelengths. The change in the optical properties is induced by the TiO2 phase transformation, which also initiates a change in the local refractive index, and assisted by the decrease of the melting point of Au on the nanoscale.

Continuous tuning of the plasmon resonance frequency of porous gold nanoparticles by mixed oxide layers

Porous gold nanoparticles (PGNs) are very popular due to their high surface/volume ratio, moreover they have stronger plasmonic properties than their solid counterparts. These properties make the porous gold nanoparticles very useful for lots of applications, for instance chemical sensors, cancer therapy applications. For applications, however, it is indispensable that the resonance frequency (RF) of a plasmonic structure to be tuneable. In this work we show that the RF can be set in a wide range as desired by coating the PGNs by mixed oxide layers. By changing the composition of the coating layer, that is the mixture ratio, the RF can be shifted practically continuously in a wide range determined by the refractive index of the used oxides. As a demonstration, PGNs were coated with mixed alumina-titania oxide layers (5–7 nm) using plasma-enhanced atomic layer deposition method. The oxide layer, beside as a tuning tool, also stabilises the structure of the PGNs when are exposed to elevated temperature. This is shown by the influence of the temperature (from 350, ^{circ }hbox {C} up to 900, ^{circ }hbox {C}) on the morphology, and as a consequence the optical extinction spectra, of the oxide coated PGNs.

SiCxNy-based resistive and threshold switching by using single precursor plasma-enhanced atomic layer deposition

In this work, SiCxNy-based resistive switching memory by using a single precursor for the back end of line (BEOL) integration has been investigated. SiCxNy films were deposited on the aluminum (Al) substrates using plasma enhanced atomic layer deposition (PEALD) method. The effects of SiCxNy chemical structure with respect to resistive switching characteristics have been studied, and the results suggest that the resistive switching mechanism is dominated by the interfacial Schottky junction with SiCxNy composition. This work not only demonstrates a PEALD method in fabricating SiCxNy-based electronics active devices but also provides additional insights into the interaction between the electrical and chemical structures in bi-functional resistive switching or threshold switching behavior. A demonstrated PEALD tool with simple single-precursor for SiCxNy deposition shows excellent feasibility to be used as functional memory and selector devices, further giving the potential pathway for advanced BEOL process integration.

A nanoporous substrate-based low temperature solid oxide fuel cell using a thin film Ni anode

A thin film solid oxide fuel cell (TF-SOFC) with a Ni anode on a nanoporous anodic aluminum oxide substrate was demonstrated. In our experiments, Ni was used as an anode material, while a very small amount of Pt was used as a cathode material, which reduced the thickness of the thin film cathode to 65 nm. In addition, a plasma-enhanced atomic layer deposition method was used to prepare a yttria-stabilized zirconia electrolyte. The open circuit voltage and the peak power density of the as-fabricated fuel cells, both of which were measured at 500 °C, were 1.04 V and 150 mW/cm2, respectively.

Study on SiN and SiCN film production using PE-ALD process with high-density multi-ICP source at low temperature

SiN and SiCN film production using plasma-enhanced atomic layer deposition (PE-ALD) is investigated in this study. A developed high-power and high-density multiple inductively coupled plasma (multi-ICP) source is used for a low temperature PE-ALD process. High plasma density and good uniformity are obtained by high power N2 plasma discharge. Silicon nitride films are deposited on a 300-mm wafer using the PE-ALD method at low temperature. To analyze the quality of the SiN and SiCN films, the wet etch rate, refractive index, and growth rate of the thin films are measured. Experiments are performed by changing the applied power and the process temperature (300–500 °C).

Remote plasma-enhanced atomic layer deposition of metallic TiN films with low work function and high uniformity

Thermal stability of metal/n-GaN contact is critical for its applications in microelectronic and optoelectronic devices. Metal Ti is generally used to make Ohmic contact on n-GaN after high temperature annealing, and the key factor is to form TiN at the interface. To reduce the processing temperature and improve the reliability, metallic titanium nitride (TiN) thin film has been proposed to substitute traditional metals (such as Ti) in the contact structures, due to its low work function and high blocking effect. For this novel approach, the first step is to fabricate high quality TiN films. Here, the authors adopted remote plasma-enhanced atomic layer deposition method to deposit TiN films under well-controlled conditions. Stoichiometric TiN films (Ti:N ∼ 1:1) with low oxygen contamination (<5%) have been deposited uniformly on 2 in. substrates in a large temperature range of 250–400 °C. The work function of TiN films is quite low (∼3.7 ± 0.1 eV) compared to metal Ti (∼4.33 eV), and almost independent to the growth temperature and substrates. Strong Fermi edge and high conductivity indicate excellent metallic property of the TiN films. This study of TiN film growth paves the way to establish a low temperature process and improve the thermal stability of Ohmic contacts for wide band gap semiconductor-based devices.

Light energy transformation over a few nanometers

Continuous platinum (Pt) thin film was fabricated via the plasma-enhanced atomic layer deposition method for a study of light energy transformation over a few nanometers. Light-to-heat experiments were used to determine the oscillating size effects on electromagnetic energy transformation in quantum wells of smooth and condensed Pt thin films. For Pt-film thicknesses of around 4 nm, 7 nm and 12 nm, electromagnetic heating presented unexpectedly high energy conversion efficiency. An empirical equation acquired from the fitting of the experimental data from various thicknesses of Pt thin films was suggested to describe the oscillating electromagnetic heating and quantized energy transformation. The experimental results show that size control of the nanostructures is extremely important for future applications involving quantum effects in nano devices.

Tuning the nanoscale morphology and optical properties of porous gold nanoparticles by surface passivation and annealing

We synthesized the arrays of porous gold nanoparticles attached to a fused silica and SiO2/Si substrates employing a combination of thin film solid state dewetting and dealloying methods. We demonstrated that the surface of porous gold nanoparticles can be passivated with a thin and conformal alumina layer produced by the plasma-enhanced atomic layer deposition method. This passivation results in significant improvement of the thermal stability of the nanoporous morphology. Whereas as–produced porous gold nanoparticles start to coarsen at the temperature as low as 160 °C, their passivated counterparts are thermally stable up to 800 °C. At higher temperatures, the solid gold nanoparticles are formed on the outer surfaces of the passivated porous gold nanoparticles, leaving behind partially emptied alumina shells. We correlated the optical absorbance spectra of the as-produced and annealed particles with their morphology and microstructure. A broad absorption peak in the infrared region was associated with thin gold ligaments of 10–15 nm in diameter, and coarsening of these ligaments in the unpassivated particles has led to the attenuation of the peak. The passivated particles demonstrated the stability of the infrared absorption intensity up to the formation of solid gold nanoparticles at 900 °C, and the red shift of the visible-range plasmon resonance peak above 600 °C. We conclude that surface passivation and heat treatments represent efficient tools for tuning surface plasmon resonance properties of porous gold nanoparticles.

Low-temperature SiON films deposited by plasma-enhanced atomic layer deposition method using activated silicon precursor

It has not been an easy task to deposit SiN at low temperature by conventional plasma-enhanced atomic layer deposition (PE-ALD) since Si organic precursors generally have high activation energy for adsorption of the Si atoms on the Si-N networks. In this work, in order to achieve successful deposition of SiN film at low temperature, the plasma processing steps in the PE-ALD have been modified for easier activation of Si precursors. In this modification, the efficiency of chemisorption of Si precursor has been improved by additional plasma steps after purging of the Si precursor. As the result, the SiN films prepared by the modified PE-ALD processes demonstrated higher purity of Si and N atoms with unwanted impurities such as C and O having below 10 at. % and Si-rich films could be formed consequently. Also, a very high step coverage ratio of 97% was obtained. Furthermore, the process-optimized SiN film showed a permissible charge-trapping capability with a wide memory window of 3.1 V when a capacitor structure was fabricated and measured with an insertion of the SiN film as the charge-trap layer. The modified PE-ALD process using the activated Si precursor would be one of the most practical and promising solutions for SiN deposition with lower thermal budget and higher cost-effectiveness.

Growing aluminum nitride films by Plasma-Enhanced Atomic Layer Deposition at low temperatures

Aluminum nitride films have been grown by Plasma-Enhanced Atomic Layer Deposition method. It was found that at temperatures of 250 °C and 280 °C increase of the plasma exposure step duration over 6 s, as well as increase of reactor purge step duration over 1 s does not affect the growth rate, however, it affects the microstructure of the films. It was found that crystalline aluminum nitride films deposit with plasma exposure duration over 10 s and the reactor purging over 10 s. When the temperature drops the increase of reactor purge step duration and plasma exposure step duration over 20 s is required for crystalline AlN film growth.

Characteristics of SiOC(-H) Thin Films Prepared by Using Plasma-enhanced Atomic Layer Deposition

Low-dielectric-constant SiOC(-H) thin films were prepared on p-type Si(100) substrates by using plasma-enhanced atomic layer deposition (PEALD) with trimethylsilane (TMS; (CH3)3SiH) and oxygen gas as precursors and Ar as a purge gas. The adoption of the atomic layer deposition (ALD) method to deposit low-k materials is a challenge to achieve high-quality films and lowtemperature process conditions. The eect of the radio-frequency (rf) power on the structural and the dielectric properties was studied. RF powers from 100 W to 500 W were applied to the PEALD system to generate the plasma. The films were analyzed by using Fourier-transform infrared (FTIR) spectroscopy and C-V and I-V measurements. FTIR studies were carried out in the absorbance mode in the range of 700 to 4000 cm 1 , and showed various bonding configurations, such as Si-O-Si(C), Si-CH3, -OH, and CHn bonds, in the films. As the rf power was increased, the absorption peaks corresponding to the Si-O-Si and the Si-O-C bonds become sharper; at the same time, the former shifted towards lower wave number (red shift). The dielectric constants of the films were investigated using a Al/SiOC(-H)/p-Si MIS structure. The measured dielectric constant and leakage current density were 2.3 and 10 8 A/cm 2 at 1 MV/cm, respectively. Using the optimized process conditions, we evaluated the PEALD method applied to SiOC(-H) film deposition. The PEALD method without heat treatment for SiOC(-H) film deposition has been shown not only to be comparable to the PECVD method with heat treatment or UV irradiation but also to be applicable to a new applications requiring a low-temperature process.

A low-temperature-grown TiO2-based device for the flexible stacked RRAM application

Flexible TiO2 crossbar memory device arrays were fabricated on plastic substrates using amorphous titanium oxidethin films grown by the low-temperature plasma-enhanced atomic layer deposition method. Al/TiO2 /Al memory cells on polyethersulfone (PES) showed an enhanced endurance property (up to104 cycles) and low switching voltages compared to the cells on rigid substrates. Themulti-stacked memory arrays were constructed by forming the additional Al/TiO2 /Al layer on the first memory device layer. Memory cells on each layer exhibited stableswitching characteristics and mechanical robustness without interlayer cell-to-cellinterference.

Growth Temperature Dependence of TiO2 Thin Films Prepared by Using Plasma-Enhanced Atomic Layer Deposition Method

Growth Temperature Dependence of TiO2 Thin Films Prepared by Using Plasma-Enhanced Atomic Layer Deposition Method

Barrier Characteristics of HfN Films Deposited by Using the Remote Plasma-Enhanced Atomic Layer Deposition Method

not Available.