Al Doping Concentration Research Articles

Electromagnetic interference shielding behaviors of Zn-based conducting oxide films prepared by atomic layer deposition

Abstract The structural, electrical, and optical properties of undoped ZnO, F-doped ZnO (ZnO:F), and Al-doped ZnO (ZnO:Al) thin films with two different thicknesses deposited by atomic layer deposition (ALD) were investigated to evaluate the electromagnetic interference shielding effectiveness (EMI-SE). A diluted fluoride hydroxide was used as a single reactant source for F doping in a ZnO matrix, and the F doping concentration was about 1 at.% in the ZnO:F films. The fabrication of the ZnO:Al films was followed by the typical ALD method, and the Al doping concentration of about 2 at.% was adjusted by the dopant deposition intervals of the ZnO:Al2O3 precursor pulse cycle ratios, which were fixed at 19:1. The film thickness variations were controlled with 600 and 1600 total ALD cycles of approximately 100 nm and 300 nm, respectively. The carrier concentration of the films is monotonically increased in order of the undoped ZnO, ZnO:F, and ZnO:Al films. The EMI-SE values of the undoped ZnO, ZnO:F, and ZnO:Al films at 1 GHz were 0.9 dB, 2.6 dB, and 6.0 dB for ~ 100 nm, and were 2.1 dB, 9.7 dB, and 13.1 dB for ~ 300 nm, respectively. In our work, the EMI-SE value was increased by the enhancement of both the carrier concentration and film thickness due to reflection via the free carrier scattering effect.

Structural and optical characterization of Zn0.95−xMg0.05AlxO nanoparticles

The structural and optical properties of ZnO nanoparticles doped simultaneously with Mg and Al were investigated. XRD results revealed the hexagonal wurtzite crystalline structure of ZnO. The FE-SEM study confirmed the formation of nano-sized homogeneous grains whose sizes decreased monotonously with increasing doping concentrations of Mg and Al. The absorption spectra showed that band gap increased from 3.20 to 3.31eV with Mg doping. As the Al concentration changed from x=0.01 to x=0.06mol% at constant Mg concentration the band gap observed to be decreased. Particle sizes estimated from effective mass approximation using absorption data and these values are in good agreement with the crystallite sizes calculated from XRD data. Raman spectra of ZnO showed a characteristic peak at 436cm−1 correspond to a non-polar optical phonon E2 (high). With increase of the Al doping concentrations, E2 (high) phonon frequency shifted to 439cm−1 from to 436cm−1. The origin of E2 (high) peak shift in ZnO nanoparticles is attributed to optical phonon confinement effects or the presence of intrinsic defects on the nanoparticles. PL spectra indicated that with increase of Al co-doping along with Mg into ZnO, intensity of the peak positioned at 395nm was initially increased at x=0 and then decreased with increase of the Al concentrations from x=0.01 to x=0.06mol%.

Size- and morphology-dependent optical properties of ZnS:Al one-dimensional structures.

Typical morphology substrates can improve the efficiency of surface-enhanced Raman scattering; the need for SERS substrates of controlled morphology requires an extensive study. In this paper, one-dimensional ZnS:Al nanostructures with the width of approximately 300 nm and the length of tens um, and micro-scale structures with the width of several um and the length of tens um were synthesized via thermal evaporation on Au-coated silicon substrates and were used to study their size effects on Raman scattering and photoluminescent spectra. The photoluminescence spectra reveal the strongest green emission at a 5 at% Al source, which originates from the Al-dopant emission. The Raman spectra reveal that the size and morphology of the ZnS:Al nanowires greatly influences the Raman scattering, whereas the Al-dopant concentration has a lesser effect on the Raman scattering. The observed Raman scattering intensity of the saw-like ZnS:Al nanowires with the width of tens nm was eight times larger than that of the bulk sample. The enhanced Raman scattering can be regarded as multiple scattering and weak exciton—phonon coupling. The branched one-dimensional nanostructure can be used as an ideal substrate to enhance Raman scattering.

Effects of a Pretreatment on Al-Doped ZnO Thin Films Grown by Atomic Layer Deposition

In this study, we investigated the electrical, structural, and optical properties of Al-doped ZnO (AZO) thin films approximately 50 nm thick grown by atomic layer deposition (ALD) on glass substrates at 200 °C. An H2O pretreatment was conducted for all AZO samples. The electrical properties of the AZO thin film were improved after the pretreatment process. The Al doping concentrations were controlled by inserting an Al2O3 cycle after every "n" ZnO cycles while varying n from 99 to 16. As the doping concentration increases, the resistivity decreases and the optical band gap increases. When the Al2O3 cycle ratio is 5%, the electrical resistivity showed the lowest value of 4.66 x 10(-3) Ω cm. A carrier concentration of 1.10 x 10(20) cm(-3), and the optical transmittance exceeding 90% were obtained in the visible and near-infrared region. The thin film was strongly textured along the (100) direction in the X-ray diffraction patterns.

Characteristics of atomic layer deposited transparent aluminum-doped zinc oxide thin films at low temperature

Various aluminum-doped zinc oxide (AZO) films were prepared on Si substrate by atomic layer deposition (ALD) at 100 °C. The effect of the composition of AZO films on their electrical, optical characteristics, structural property and surface topography was investigated. The appearance of electrical resistivity shows their semiconducting properties. In most of the visible light band, all the AZO films present transparency of more than 80 %. Al doping suppresses the AZO film crystallization. When the Al doping concentration increases up to 3.95 at%, the AZO film has some small multicrystal grains with random orientation. Al doping improves the roughness of i-ZnO film. The root mean square (RMS) roughness of samples prepared by ALD is much smaller than that prepared by radio-frequency magnetron sputtering reported.

Enhanced thermal stability of alpha gallium oxide films supported by aluminum doping

In order to enhance the thermal stability of corundum-structured gallium oxide (α-Ga2O3), which is attractive for use in wide-band-gap heterostructure devices and amenable to band gap and function engineering but suffers from phase transformation in high-temperature growth (>500 °C) and treatments (>550 °C), we attempted aluminum (Al) doping. The thermal stability of the films was enhanced by increasing the Al doping concentration, and under the best doping conditions where the Al concentration was negligible compared with the basic chemical composition of Ga2O3, the growth and successive thermal treatment temperatures were increased to as high as 650 and 750 °C, respectively, without the marked appearance of the β-gallia phase. Under the doping conditions above, the inclusion of Al was not negligible at the growth temperature of 800 °C and the film composition was expressed as an alloy of α-(Al0.2Ga0.8)2O3, but this film remained as the α-phase at annealing temperatures up to 900 °C. Enhanced thermal stability widens the device process windows, contributing to the formation of various high-performance devices.

Synthesis of High Crystalline Al‐Doped ZnO Nanopowders from Al2O3 and ZnO by Radio‐Frequency Thermal Plasma

High crystalline Al‐doped ZnO (AZO) nanopowders were prepared by in‐flight treatment of ZnO and Al2O3 in Radio‐Frequency (RF) thermal plasma. Micron‐sized (~1 μm) ZnO and Al2O3 powders were mixed at Al/Zn ratios of 3.3 and 6.7 at.% and then injected into the RF thermal plasma torch along the centerline at a feeding rate of 6.6 g/min. The RF thermal plasma torch system was operated at the plate power level of ~140 kVA to evaporate the mixture oxides and the resultant vapor species were condensed into solid particles by the high flow rate of quenching gas (~7000 slpm). The FE‐SEM images of the as‐treated powders showed that the multipod shaped and the whisker type nanoparticles were mainly synthesized. In addition, these nanocrystalline structures were confirmed as the single phase AZO nanopowders with the hexagonal wurtzite ZnO structure by the XRD patterns and FE‐TEM results with the SAED image. However, the composition changes of 0.3 and 1.0 at.% were checked for the as‐synthesized AZO nanopowders at Al/Zn ratios of 3.3 and 6.7 at.%, respectively, by the XRF data, which can require the adjustment of Al/Zn in the mixture precursors for the applications of high Al doping concentrations.

Structure and electrical properties of Al-doped HfO₂ and ZrO₂ films grown via atomic layer deposition on Mo electrodes.

The effects of Al doping in atomic-layer-deposited HfO2 (AHO) and ZrO2 (AZO) films on the evolutions of their crystallographic phases, grain sizes, and electric properties, such as their dielectric constants and leakage current densities, were examined for their applications in high-voltage devices. The film thickness and Al-doping concentration were varied in the ranges of 60-75 nm and 0.5-9.7%, respectively, for AHO and 55-90 nm and 1.0-10.3%, respectively, for AZO. The top and bottom electrodes were sputtered Mo films. The detailed structural and electrical property variations were examined as functions of the Al concentration and film thickness. The AHO films showed a transition from the monoclinic phase (Al concentration up to 1.4%) to the tetragonal/cubic phase (Al concentration 2.0-3.5%), and finally, to the amorphous phase (Al concentration >4.7%), whereas the AZO films remained in the tetragonal/cubic phase up to the Al concentration of 6.4%. For both the AHO and AZO films, the monoclinic and amorphous phases had dielectric constants of 20-25, and the tetragonal/cubic phases had dielectric constants of 30-35. The highest electrical performance levels for the application to the high-voltage charge storage capacitors in flat panel displays were achieved with the 4.7-9.7% Al-doped AHO films and the 2.6% Al-doped AZO films.

Sol–gel production of Cu/Al co-doped zinc oxide: Effect of Al co-doping concentration on its structure and optoelectronic properties

Sol–gel deposition of ZnO:Cu:Al thin films were co-doped different Cu:Al ratio. The optoelectronic and structural properties of the resultant film were evaluated using scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy, photoluminescence spectroscopy and UV–VIS spectroscopy. It was found that the Al content leads to narrowing of the band gap and that excessive Al doping concentration greater than 5at% degrade the film’s properties.

Enhancement of open-circuit voltage on organic photovoltaic devices by Al-doped TiO2 modifying layer produced by sol–gel method

Sol–gel method has shown several advantages for oxide synthesis, such as lower cost production, coating large areas, lower processing temperatures and ease insertion of doping materials. Therefore, it is attractive for production of intermediate and electrode modifying layers in organic optoelectronic devices. Herein, spin-coated aluminum-doped titanium dioxide (AlTiO2) thin films were produced by sol–gel method onto glass and fluorine-doped tin oxide (FTO) substrates, using different Al-dopant concentrations and post-done annealing temperatures. Electrical measurements were performed in order to investigate the improvement of the TiO2 resistivity. Additionally, structural, compositional, morphological, optical and electrical properties of the optimal AlTiO2 modifying layers onto FTO substrates were probed by different techniques, and compared with those obtained from the undoped thin films produced under similar conditions. Organic photovoltaic devices (OPVs) with the structure FTO/AlTiO2(30nm)/C60(50nm)/CuPc(50nm)/Al with an Al concentration of 0.03M in AlTiO2 layer were produced. The insertion of AlTiO2 thin films improved the short-circuit current density (Jsc) as well as the open circuit voltage (Voc) in comparison with non-modified electrode FTO based devices. This behavior is discussed in terms of induced interface phenomena as dipole formation induced by Al.

Preparation and electromagnetic property of Al-doped SnO2 powders by coprecipitation method in the GHz range

Al-doped SnO2 powders have been prepared by coprecipitation method at 550 °C, using tin chloride (SnCl4·5H2O) as the raw material, ammonium hydroxide (NH3·H2O) as the precipitator, and aluminum nitrate (Al(NO3)3·9H2O) as the doping source, respectively. The microstructure of the prepared powders has been characterized by X-ray diffraction and scanning electron microscope, respectively. Results show that the prepared powders were Sn(1−x)AlxO2 (x = 0, 0.03, 0.06, and 0.09) solid solution powders and the lattice constant decreased with increasing Al doping content. The electromagnetic property in the frequency range of 8.2–12.4 GHz of prepared powders has been determined. The real part (e′) and imaginary part (e″) of permittivity of prepared powders increased with increasing Al doping content. There was little change of real part (μ′) and imaginary part (μ″) of permeability of prepared powders. The electromagnetic loss mechanism has been discussed.

Properties of nanostructured Al doped ZnO thin films grown by spray pyrolysis technique

Aluminium doped zinc oxide thin films were deposited on glass substrate by using spray pyrolysis technique. The X-ray diffraction study of the films revealed that the both the undoped and Al doped ZnO thin films exhibits hexagonal wurtzite structure. The preferred orientation is (002) for undoped and up to 3 at % Al doping, further increase in the doping concentration to 5 at % changes the preferred orientation to (101) direction. The surface morphology of the films studied by scanning electron microscope, reveal marked changes on doping. Optical study indicates that both undoped and Al doped films are transparent in the visible region. The band gap of the films increased from 3.24 to 3.36 eV with increasing Al dopant concentration from 0 to 5 at % respectively. The Al doped films showed an increase in the conductivity by three orders of magnitude with increase in doping concentration. The maximum value of conductivity 106.3 S/cm is achieved for 3 at % Al doped films.

Aluminum doping of CuInSe2 synthesized by solution process and its effect on structure, morphology, and bandgap tuning

Al-doped CuInSe2 material is prepared by a low-cost wet chemical process. The key properties of Al-doped CuInSe2 as a successful solar cell material are investigated, such as crystal structure, morphology, optical properties, and bandgap. In situ X-ray diffraction measurements indicate that the doping of Al has induced noticeable lattice distortion. The material shows excellent thermal stability up to 600 °C annealing temperature. By increasing the Al-doping concentration, the crystal unit-cell parameter of the material becomes smaller and the change of crystal structure leads to an increase of the grain size and surface roughness. The bandgap of Al-doped CuInSe2 can be continuously tuned in a range of 1.07–1.67 eV as Al/(Al + In) content ratio varies from 0 to 0.49. Finally, the effect mechanism on the properties of CuInSe2 after Al doping is discussed based on the ionic radius, crystal structure, and bonding state.

A detailed investigation of electronic and intersubband optical properties of AlxGa1−xAs/Al0.3Ga0.7As/AlyGa1−yAs/Al0.3Ga0.7As multi-shell quantum dots

In this study, we have investigated the electronic and intersubband optical properties of AlxGa1−xAs/Al0.3Ga0.7As/AlyGa1−yAs/Al0.3Ga0.7As multi-shell quantum dot heterostructures as a function of the Al doping concentrations in both the core (x) and the well (y) regions for cases with and without a hydrogenic donor impurity. Our results reveal how resonant absorption wavelengths and absorption coefficient strengths are changed by variation of the Al content in the core (x) and well (y) regions. Besides this, how the electronic and intersubband optical properties of this structure are affected by the existence of the impurity has also been shown. The physical reasons for this relationship between the electronic and optical properties of this structure and the Al content in the core and well regions have been discussed in detail.

The effects of surface morphology on optical and electrical properties of nanostructured AZO thin films: Fractal and phase imaging analysis

Highly transparent aluminum-doped ZnO (AZO) thin films were prepared by using sol–gel dip coating (SGDC) technique. The effects of Al dopant concentrations on the electrical, optical and structural properties of the AZO films were studied comprehensively. XRD results showed that all the prepared AZO films were polycrystalline and had the hexagonal wurtzite structure. As it is indicated by AFM analysis results, the enhancement of the both surface smoothness and autosimilarity of the films with increasing Al incorporation makes them suitable for optoelectronic applications. The negative surface skewness of pure and 1 at.% AZO thin films indicate porous morphology and low kurtosis while the positive skewness and higher kurtosis value of the 3 at.% sample make it favorable for nanotribological applications. The AFM phase contrast images of AZO thin films revealed the segregation of Al dopant in the grain boundaries. The optical transparency and electrical conductivity of samples enhanced with Al doping and the 1 at.% AZO thin films have the best electrical conductivity with average transmittance of 88.5% in visible region. The optical characteristics such as light absorbing and refractive index were studied based on fractal feature of AZO thin films.

First-principles study of effects of Al doping on electronic structures and optical properties of SnO2

The electronic structures and optical properties of tin dioxide (SnO2) with different Al-doping concentrations (x = 0, 0·0185 and 0·0417) are investigated using the first-principles calculation of plane wave ultra-soft pseudo-potential technology based on the density functional theory under the local-density approximation. The results show that the Fermi level of Al-doped SnO2 goes into the valence band, indicating that Al-doped SnO2 is a typical p-type semiconductor. Moreover, with the increase in Al-doping concentrations, the band gap of SnO2 is broadened and the blueshift of the absorption spectrum becomes significant, which are in good agreement with the experiment results. In addition, the low reflectivity (<15%) in the visible light range is obtained.

Controlling the Al-doping profile and accompanying electrical properties of rutile-phased TiO2 thin films.

The role of Al dopant in rutile-phased TiO2 films in the evaluation of the mechanism of leakage current reduction in Al-doped TiO2 (ATO) was studied in detail. The leakage current of the ATO film was strongly affected by the Al concentration at the interface between the ATO film and the RuO2 electrode. The conduction band offset of the interface increased with the increase in the Al dopant concentration in the rutile TiO2, which reduced the leakage current in the voltage region pertinent to the next-generation dynamic random access memory application. However, the Al doping in the anatase TiO2 did not notably increase the conduction band offset even with a higher Al concentration. The detailed analyses of the leakage conduction mechanism based on the quantum mechanical transfer-matrix method showed that Schottky emission and Fowler-Nordheim tunneling was the dominant leakage conduction mechanism in the lower and higher voltage regions, respectively. The chemical analyses using X-ray photoelectron spectroscopy corroborated the electrical test results.

A novel route to realize controllable phases in an aluminum (Al3+)-doped VO2 system and the metal–insulator transition modulation

The controllable M1 or M2 phases of Al3+-doped VO2 were successfully achieved through an effective and economical route, which combines a hydrothermal method and subsequent annealing treatment. The crystalline structure and the valence states of as-prepared samples were characterized by XRD, TEM, and XANES spectroscopy. Experiments showed that the Al3+ dopants and the Ar flux rates in an annealing process played the important roles in the formation of stable M2 phase. Microstructural characterizations by SEM indicated that the size of Al-doped VO2 particles gradually reduced with increasing Al concentration. The phase transition property measured by DSC revealed that the metal–insulator transition temperature (TC) could be tuned by the Al-doping concentration only in the formation of M2 phase.

Sol–gel derived AZO thin film with unusual narrow dual emission

AZO (Al:ZnO) nanostructured thin film was prepared by a dip coating technique. An improved sol–gel method was used for the preparation of stable AZO sol with 2at% Al dopant concentration. Optical properties of AZO thin film have been studied by UV–visible absorption and photoluminescence spectroscopy. Scanning electron microscopy and X-ray diffraction pattern were performed to study the grain size and morphology of AZO thin films. Experimental observations confirmed that the deposited AZO thin film has potential for dual narrow emission in the blue and green regions. Transmission spectrum shows that the prepared thin film is able to transmit above 95% of the light in the visible region. The prepared thin film resistivity is also very low (5.0Ωcm).

Experimental Research on the Magnetic Mechanisms of Zn&lt;sub&gt;0.990&lt;/sub&gt;Co&lt;sub&gt;0.010&lt;/sub&gt;O Diluted Magnetic Semiconductor by Al-Doping

The effect of Al-doping concentration and sintered temperature (ST) on the structure and room-temperature ferromagnetism (RTFM) of Al-doped Zn0.990Co0.010O nanocrystals was investigated. The experimental results have indicated that all samples have RTFM and are composed of wurtzite ZnO with hexagonal structure without any secondary phases. The crystallization quality is positive related to ST and negative related to Al-doping concentration. When ST is higher than 800°C, the RTFM is dominated by the long rang coupling induced from the conductive carriers of Al3+, since it is increasing with the increase of Al-doping concentration and grain sizes. When ST is lower than 800°C, the RTFM is dominated by localized carriers from oxygen vacancies, since the maximum RTFM belongs to the sample which has the lowest parameters of unit cell.