Homo-buffer Layer Research Articles

Improving crystal quality of β-phase MgGaO thin films by using low-temperature homo-buffer layer

Ultra-wide bandgap (UWBG) semiconductors are promising for many applications, such as power electronics and deep-ultraviolet photonics. In this research, UWBG β-phase magnesium gallium oxide (MgGaO) thin films with a bandgap of 5.1 eV were grown using low-temperature homo-buffer layers in a plasma-assisted molecular beam epitaxy system. The role of the growth temperature and thickness of low-temperature buffer layer on the quality of the active layer was studied using x-ray diffraction and transmission electron microscopy and by analyzing the properties of metal–semiconductor–metal photodetector devices based on these films. It is found that lower buffer growth temperature at 300 °C leads to higher crystal quality of active layer. For the same low buffer growth temperature, different crystal quality in the active layer is attained with different buffer layer thickness. A buffer layer thickness at 40 nm has the best active layer quality with the highest photo current under 265 nm illumination and long decay time as a result of reduced recombination of photo-generated carriers through fewer defects in the active layer.

Влияние гомобуферного слоя на морфологию, микроструктуру и твердость пленок Al/Si(111)

The results of complementary studies of Al films grown by magnetron sputtering at room temperature are presented. The films were obtained on standard Si(111) silicon substrates without and with a ~20 nm aluminum (homobuffer) layer preliminarily grown on their surface at 400°C. The interdependence of the morphology, microstructure, and hardness of Al films on the state of the substrate surface was studied by the HRXRR, XRD, SEM, EDS, AFM, and Nano Indenter (ASTM) methods. It is shown that the formation of homobuffer layers on the substrate surface makes it possible to control the structural and mechanical properties of thin aluminum films.

Design and Fabrication of ZnO-Based SAW Sensor Using Low Power Homo-Buffer Layer for Enhanced Humidity Sensing

Zinc oxide (ZnO) nanostructures were proven to enhance the sensitivity performance of nanoscale ZnO-based surface acoustic wave (SAW) sensor greatly. Here, we developed ZnO sensitive layer-based SAW sensors by low power homo-buffer layer (LPHBL) method and focused on the quality of preparation, their mass sensitivity and humidity sensing applications. ZnO films were prepared on the surface of the SAW devices by radio frequency magnetron sputte ring method by employing different sputtering power. Island-shape ZnO nanostructures were successfully prepared by the simple LPHBL method. The mass sensitivities of these sensor devices based on Rayleigh wave mode and Sezawa wave mode were increased dramatically by increasing ZnO top layer thickness. To evaluate the humidity sensing performance, the humidity testing experiments were conducted for a range of moisture concentrations between 1% and 95%. The ZnO/quartz sensor without LPHBL frequency response magnitudes varied between 0-19.25 kHz and insertion loss (IL) shifts changed between 0-0.815 dB for 1%-95% RH while the ZnO/ZnO/quartz SAW sensor with LPHBL showed 0-26.25 kHz response magnitudes and 0-1.878 dB IL shifts at the same conditions. The Love-SAW sensor with LPHBL exhibited more than 36% greater humidity response sensitivity compared to its no intermediate layer counterpart. In addition, the recovery of the ZnO/ZnO/quartz humidity sensing device could reach 91.5%. Overall, the ZnO-based Love-SAW sensor fabricated by the LPHBL method may hold promise for chemical and biological detection applications.

Direct-epitaxial growth of SrAl2O4:Eu,Dy thin films on Al2O3 substrate by pulsed laser deposition

Europium (Eu) and dysprosium (Dy) co-doped strontium aluminate (SrAl2O4) (SA:Eu,Dy) is one of the most widely applied long persistent phosphors due to its strong emission intensity and long afterglow. However, the difficulty to get crystalline SA:Eu,Dy thin films in the as-deposited state strongly limited their applications in devices and surface coatings. In this study, we present a breakthrough in the synthesis of single-crystal SA:Eu,Dy films via direct-epitaxial growth on sapphire substrate by means of pulsed layer deposition. A threshold temperature of 900 °C is identified, only above which the mobility of adatoms is high enough to form crystalline films. By avoiding the nucleation process via introducing a homo-buffer layer, this temperature can be significantly reduced by 200 °C. The direct-epitaxial growth ensures a good surface quality, while the temperature reduction may prevent interdiffusion in applications involving hetero multilayer structures. The films are single crystals composed of twinned domains. The constraint effect from substrate significantly limits the freedom for twinning, which leads to much less twin variants in films compared to powders. The high-quality epitaxial films obtained in this study are useful for understanding the unique phosphorescence mechanism in SA:Eu,Dy, which may further help to design new phosphor materials with higher performance.

Effect of Homo-buffer Layers on the Properties of Sputtering Deposited Ga2O3 Films

β- Ga2O3 films were grown by radio-frequency magnetron sputtering method. The influence of Ga2O3 buffer layers and annealing treatment on the structural, optical, morphological and electrical properties of Ga2O3 films was studied. The results revealed an improvement of crystalline quality and transmittance of annealed β- Ga2O3 films prepared with homo-buffer layers. Ga2O3 film UV photodetectors were fabricated with a new B and Ga co-doped ZnO films (BGZO)/Au interdigitated electrode. A good ohmic contact was formed between the film and the electrode. For the detector based on Ga2O3 films with buffer layers, a higher value of photo response and faster response times was obtained.

Influence of homo-buffer layers and post-deposition rapid thermal annealing upon atomic layer deposition grown ZnO at 100 °C with three-pulsed precursors per growth cycle

ZnO main epilayers are deposited with three-pulsed precursors in every growth cycle at 100°C on various thicknesses of 300°C-grown homo-buffer layers by atomic layer deposition (ALD) on sapphire substrate. Samples are treated without and with post-deposition rapid thermal annealing (RTA). Two different annealing temperatures 300 and 1000°C are utilized in the ambience of oxygen for 5 min. Extremely low background electron concentration 8.4×1014cm−3, high electron mobility 62.1cm2/V s, and pronounced enhancement of near bandgap edge photoluminescence (PL) are achieved for ZnO main epilayer with sufficient thickness of buffer layer (200 ALD cycles) and post-deposition RTA at 1000°C. Effective block and remove of thermally unstable mobile defects and other crystal lattice imperfections are the agents of quality promotion of ZnO thin film.

Gradient Al-doped ZnO multi-buffer layers: Effect on the photovoltaic properties of organic solar cells

In this work, gradient Al-doped ZnO multi-buffer layers (MBLs) were used as the electron transport layers (ETLs) of organic solar cells (OSCs) for the first time. Three kinds of MBLs were prepared using a facile sol–gel process and deposited on a homo-buffer layer (ZnO). Compared to a device based on a multi-ZnO buffer layer, devices with the gradient-doped MBL displayed enhanced power conversion efficiency from 2.11% to 3.43%, which were caused by the efficient light transmission and charge carrier transport, derived from the higher film qualities, denser and more uniform surface morphologies, and improved conductivities of the gradient-doped MBLs. Results indicated that a device with ZnO/MBL (0.5:1.0at%(Al/Zn)) simultaneously enhanced the short-circuit current and fill factor. This study presents an innovative and effective method for improving the quality of ETLs for efficient OSCs.

The influence of homo-buffer layer on structural, optical and electrical properties of ZnO:Al films

Aluminum-doped ZnO (AZO) films were fabricated on glass by pulsed-laser deposition based on orthogonal design, and influences of homo-buffer layer on structural, optical and electrical properties of AZO films were investigated. The experiment results demonstrate that the homo-buffer layer is very beneficial to improve the quality of AZO films. In addition, both deposition temperature of homo-buffer layer (Thomo-buffer) and deposition oxygen pressure of homo-buffer layer (Phomo-buffer) have a considerable influence on the properties of AZO films. By optimizing the deposition parameters of homo-buffer layer and AZO film synthetically, the AZO film with low resistivity (2.13×10−4Ωcm) and high transmittance (89.1%) has been obtained, which is a promising candidate material in transparent electrode applications.

Preparation and mechanoluminescent properties of SrAl2O4:Eu film grown on silicon substrate using double buffer layers

In this paper, we utilized double layer method to prepare SrAl2O4:Eu (SAOE) film on silicon substrate (400). The Al2O3 layer (about 200nm) was used as a hetero-buffer layer to eliminate the large difference of crystal lattice and thermal mismatch between the SAOE and silicon substrate. Thin SAOE layer (about 600nm) was grown on Al2O3 layer as homo-buffer layer to reduce internal stress during film growth process. On double buffer layers, continuous sputtering formed about 1.5μm SAOE film. The resulting thick SAOE/Al2O3/Si film possessed both excellent photoluminescence (PL) and mechanoluminescence (ML) properties. The similarity of PL and ML spectra suggested that PL and ML both originated from same emitting center of Eu2+. The strong ML intensity showed that the as-prepared SAOE film can be regarded as an indicator to detect stress distribution of an object. The thermoluminescent (ThL) results indicated that a large amount of trapped electrons existing in the resulting film answered for the strong ML intensity.

Zinc Oxide Buffer Layer Insertion for Sensitivity Improvement in Aluminium-Doped Zinc Oxide-Based Humidity Sensors

The improvement of sensitivity toward humidity by insertion of buffer layer has been investigated. The insertion of hetero- or homo-buffer layer of zinc oxide (ZnO) thin film before deposition of high quality ZnO had been reported for the growth on highly mismatched substrate. Three samples are characterized with different properties which are as deposited ZnO thin film without buffer layer (as deposited ZnO thin film) , anneal ZnO thin film without buffer layer (ZnO thin film) and anneal ZnO thin film with buffer layer (ZnO/ AZO thin film). The structural properties of ZnO thin film has been characterized field emission scanning electron microscopy (FESEM) JEOL JSM 6701F, atomic force microscope AFM (Park System XE-100) and XRD (Rigaku Ultima IV). The electrical and optical properties has been characterized using 2 point probe I-V measurement (Keithley 2400) and UV-Vis spectrophotometer (JASCO 670) respectively. In this work, we have focused on investigating the humidity sensitivity of ZnO thin film deposited using RF magnetron sputtering (SNTEK RSP 5004-PVD) with and without the buffer layer (Aluminum-doped ZnO (AZO)) for humidity sensor application.

High quality epitaxial ZnO films grown on solid-phase crystallized buffer layers

High quality epitaxial ZnO films on sapphire (110) plane have been fabricated on ZnO homo-buffer layers crystallized via solid-phase epitaxially (SPE). The SPE-ZnO films are fabricated by annealing of amorphous ZnON (a-ZnON) films deposited by RF magnetron sputtering. During annealing, the a-ZnON films are oxidized and converted to ZnO crystal. X-ray diffraction (XRD) analysis shows that the resultant films are epitaxially grown on the sapphire substrates. By using the SPE-ZnO films as homo-buffer layers, the ZnO films with high crystallinity, which are deposited by RF magnetron sputtering, are fabricated. The full width at half-maximum of XRD patterns for 2θ-ω and ω scan of (002) plane are 0.094° and 0.12°, respectively, being significantly small compared with 0.24° and 0.55° for the films without buffer layers. Thus utilizing SPE buffer layers is very promising to obtain epitaxial ZnO films with high crystallinity.

Implementation of High Carrier Mobility in Al-N Codoped p-Type ZnO Thin Films Fabricated by Direct Current Magnetron Sputtering with ZnO:Al2O3Ceramic Target

In this study, Al-N codoped p-type zinc oxide (ZnO) thin films were deposited on Si and homo-buffer layer templates in a mixture of and gas with ceramic ZnO:(2 wt% ) as a sputtering target using DC- magnetron sputtering. X-ray diffraction spectra of two-theta diffraction showed that all films have a predominant (002) peak of ZnO Wurtzite structure. As the fraction in the mixed and gases increased, field emission secondary electron microscopy revealed that the surface appearance of codoped films on Si varied from smooth to textured structure. The p-type ZnO thin films showed carrier concentration in the range of , resistivity in the range of 131.2-2.864 , and mobility in the range of respectively.

Growth and Application of High Quality ZnO Films Grown on Diamond Substrates

Highly c-axis oriented ZnO films were grown on the nucleation sides of freestanding diamond (FSD) substrates with homobuffer layer by radio-frequency (RF) magnetron sputtering method. The effect of oxygen partial pressure (O2/Ar) on the properties of ZnO films was studied. ZnO-based UV photoconductive detector with planar interdigital (IDT) electrodes was fabricated by the lift off technique. Current-voltage (I-V) characteristics of the detector under ultraviolet (UV) light were measured and discussed.

Homobuffer thickness effect on the background electron carrier concentration of epitaxial ZnO thin films

Epitaxial ZnO thin films were grown on r-plane sapphire substrates using plasma-assisted molecular-beam epitaxy. ZnO homobuffer layers grown at a lower temperature were introduced to improve the crystallinity of the top ZnO thin films. Thicker homobuffer layers lead to better crystallinity of the subsequent epitaxial ZnO thin films due to the strain relaxation effect. Residual background electron carrier concentration in these undoped ZnO thin films first decreases, then increases as the buffer layer thickness increases from ∼1 to 30 nm, with a minimum electron concentration of ∼1×1017 cm−3 occurring in ZnO homobuffer of ∼5 nm. These results demonstrate that the optimized ZnO homobuffer thickness to achieve both good ZnO crystallinity and low residual electron concentration is determined by the relative electron carrier concentration ratios and mobility ratios between the buffer and epi-ZnO layers.

Microstructural Properties at the Interfaces of ZnO Nanorods and ZnO Homo-Buffer Layers

Uniformly and vertically well-aligned ZnO nanorods were fabricated in-situ and ex-situ on ZnO films using a catalyst-free metal-organic chemical vapor process. Microstructural properties of the initial growth of ZnO nanorods on ZnO films with different surface roughnesses were investigated. We observed that the ZnO nanorods grown on ZnO films with surface roughness of less than 1.0 nm were well-aligned along the c-axis and in the ab-plane. When the nanorods grew on ZnO films with a large surface roughness, they had three different growth directions of 28 degrees, 62 degrees, and 90 degrees to the film surface. The slant angle of 62 degrees corresponds to the angle between the ZnO(001) and (101) planes. The initial growth direction difference caused structural disorder at the interface of the ZnO nanorod and film, and prevented epitaxial growth and the alignment of the nanorods.

Improvement in crystal quality of ZnO film on Si substrate by using a homo-buffer layer

Abstract ZnO thin films without and with a homo-buffer layer have been prepared on Si(1 1 1) substrates by pulsed laser deposition (PLD) under various conditions. Photoluminescence (PL) measurement indicates that the optical quality of ZnO thin film is dramatically improved by introducing oxygen into the growth chamber. The sample deposited at 60 Pa possesses the best optical properties among the oxygen pressure range studied. X-ray diffraction (XRD) results show that the films directly deposited on Si are of polycrystalline ZnO structures. A low-temperature (500 °C) deposited ZnO buffer layer was used to enhance the crystal quality of the ZnO film. Compared to the film without the buffer layer, the film with the buffer layer exhibits aligned spotty reflection high-energy electron diffraction (RHEED) pattern and stronger near-band-edge emission (NBE) with a smaller full-width at half-maximum (FWHM) of 98 meV. The structural properties of ZnO buffer layers grown at different temperatures were investigated by RHEED patterns. It is suggested that the present characteristics of the ZnO epilayer may be raised further by elevating the growth temperature of buffer layer to 600 °C.

Preparation of ZnO Thin Films on Free-Standing Diamond Substrates

Highly c-axis-oriented ZnO films were deposited successfully on the nucleation sides of free-standing diamond (FD) films by the direct current (DC) magnetron sputtering method. The effect of the sputtering parameters, such as power, gas pressure and sputtering plasma composition of Ar-to-O2, on the properties of ZnO thin films was investigated in detail. X-ray diffraction (XRD) measurements showed that, at a sputtering power of 200 W, gas pressure of 0.5 Pa and an Ar-to-O2 composition of 1:1, a higher intensity of the (002) diffraction peak and a narrower full width at half maximum (FWHM) were detected which meant high c-axis orientation and high quality of the ZnO films. To improve the quality of the ZnO film, a thin ZnO layer was pre-grown as a homo-buffer layer. XRD measurements showed that this buffer layer had a beneficial effect on the structural and morphological properties of the post-grown ZnO film.

Photoluminescence enhancement by rapid thermal annealing for ZnO epitaxial films grown on Si (100) by pulsed laser deposition

ZnO single-crystalline films were prepared by predepositing a homobuffer layer on Si (100) substrate in a pulsed laser deposition system. The effect of short-time rapid thermal annealing under N2 and O2 ambient on the optical property was systematically studied by photoluminescence measurements from 77K to room temperature. Different from the adverse effect of the O2-assisted rapid thermal annealing on the optical quality, N2-assisted rapid thermal annealing can greatly enhance the ultraviolet emission while eliminate the deep-level emission band including separate green, yellow, and orange luminescence peaks. Such ambient-dependent photoluminescence enhancement was attributed to the elimination of oxygen interstitial in the ZnO film.

In-situ and ex-situ ZnO nanorod growth on ZnO homo-buffer layers

Vertically well-aligned ZnO nanorods were fabricated in-situ and ex-situ on ZnO homo-buffer layers using catalyst-free metal-organic chemical vapor deposition. Field-emission electron microscopy measurements demonstrated that the nanorods were well aligned and had a uniform diameter of 70–100 nm depending on the growth temperature, irrespective of growth conditions, in-situ and ex-situ. X-ray diffraction measurements demonstrated that the ZnO nanorods and the ZnO buffer layers had a wurtzite structure, and that the crystal quality of the nanorods grown on a smooth surface was better than that of the nanorods grown on a rough surface. Field-emission transmission electron microscopy measurements revealed the presence of a disordered layer at the interface of the nanorod and the buffer layer.

Vertically Aligned Ultraslim ZnO Nanowires Formed by Homobuffer: Growth Evolution and Emission Properties

Vertically aligned, ultraslim ZnO nanowire arrays, ≤ 10 nm in diameter, were fabricated by depositing a homobuffer layer on a Si substrate by metalorganic chemical vapor deposition and their growth mechanism was examined. During the heating process, the side facet planes of the nanosheets were transformed from high index planes, such as (0113) and (0112), to low index planes, such as (0111) and (0110), which is related to the available surface energy during growth. The ultraslim nanowires exhibited extremely intense ultraviolet emission with enhanced thermal activation energy in the photoluminescence measurements as well as excellent field-emission performance with intense brightness and a low turn-on field. This extraordinary emission performance of the ultraslim ZnO nanowires was attributed to the concurrent achievement of high crystalline quality and the vertical alignment of the ultraslim nanowires with the appropriate density at high temperatures.