CERCETĂRI XRD ȘI XPS ALE STRATURILOR DE AlN, AlGaN, GaN DEPUSE PE SILICIU PRIN METODA HVPE

Prin metoda reacțiilor chimice de transport HVPE (Hydride Vapor Phase Epitaxy) in sistemul (H2-NH3-HCl-Al-Ga-Si) au fost sintetizate straturi subțiri de AlN, AlGaN, GaN pe substraturi de siliciu, Si(111). Morfologia suprafeței, precum și a secțiunilor transversale ale structurilor a fost cercetată prin metoda SEM (Scanning Electron Microscopy) de rezoluție înaltă. Compoziția în secțiune transversală a structurilor a fost studiată prin metoda XRD (X-Ray Diffraction method), iar de suprafață – prin metoda XPS (X-Ray Photoelectronic Spectroscopy). Afară de aluminiu, galiu și azot în straturi au fost depistate oxigen și carbon. S-a stabilit că concentrația oxigenului pe suprafața straturilor de GaN, depuse la temperaturi relativ mai joase, este mai mică. Se presupune că concentrația ridicată a oxigenului în straturi are loc în urma descompunerii cuarțului, din care este confecționat reactorul, la temperaturi ridicate. S-a constatat că încorporarea galiului în straturile de AlGaN este diminuată de fluxul precursorilor aluminiului. Prin aceasta se demonstrează că viteza reacțiilor chimice ale precursorilor azotului cu ale aluminiului este semnificativ mai mare decât cu ale galiului, ultimele fiind înlăturate din zona de depunere de fluxul gazului de transport.XRD AND XPS INVESTIGATIONS OF THE AlN, AlGaN, GaN LAYERS DEPOSITED ON SILICON BY THE HVPE METHODUsing the HVPE (Hydride Vapor Phase Epitaxy) transport method, in system (H2-NH3-HCl-Al-Ga-Si), thin layers of AlN, AlGaN, GaN on silicon substrates were synthesized. Surface morphology as well as transverse sections of structures was investigated by the high resolution SEM (Scanning Electron Microscopy) method. The cross-sectional composition of the structures was studied by the X-Ray Diffraction Method (XRD) and Surface X-Ray (X-Ray Photoelectronic Spectroscopy). Outside of aluminum, gallium and nitrogen in the layers were detected oxygen and carbon. It has been established that the concentration of oxygen on the surface of the GaN layers deposited at relatively lower temperatures is lower. It is assumed that the high concentration of oxygen in the layers takes place after the decomposition of the quartz, from which the reactor is made, at high temperatures. It has been found that the incorporation of gallium into the AlGaN layers is diminished by the flux of aluminum precursors. This demonstrates that the rate of chemical reactions of the nitrogen precursors with the aluminum is significantly higher than with the latter being removed from the deposition area by the transport gas stream.</p

Highly Porous and Ultra-Lightweight Aero-Ga2O3: Enhancement of Photocatalytic Activity by Noble Metals

A new type of photocatalyst is proposed on the basis of aero-β-Ga2O3, which is a material constructed from a network of interconnected tetrapods with arms in the form of microtubes with nanometric walls. The aero-Ga2O3 material is obtained by annealing of aero-GaN fabricated by epitaxial growth on ZnO microtetrapods. The hybrid structures composed of aero-Ga2O3 functionalized with Au or Pt nanodots were tested for the photocatalytic degradation of methylene blue dye under UV or visible light illumination. The functionalization of aero-Ga2O3 with noble metals results in the enhancement of the photocatalytic performances of bare material, reaching the performances inherent to ZnO while gaining the advantage of the increased chemical stability. The mechanisms of enhancement of the photocatalytic properties by activating aero-Ga2O3 with noble metals are discussed to elucidate their potential for environmental applications

ZINC OXIDE THIN FILMS PREPARED BY SPRAY PYROLYSIS TECHNIQUIE IN ARGON FLOW

ZnO thin layers were grown from zinc acetate dissolved in methanol-acetic acid-water solution with the molarity of 0.2M by using the pulverization method in an argon flow at the temperatures of 250-450°C. The temperature dependence of electrical and optical properties of the obtained layers were studied. The optical transmittance at the wavelengths of (300 -1000) nm has the values of 80-85%. The resistivity of ZnO thin layers grown at 450°C decreases from 33W•cm to       0,028 W•cm after annealing in hydrogen at 450°C during an hour. The radiative recombination is related to the electron transitions to the deep levels and band to band transitions at the charge carriers transitions with the LO type phonons.</p

CELULE FOTOVOLTAICE CU HETEROJONCȚIUNEA n+CdS-po-p+InP: APLICĂRI TEHNOLOGICE, METODE ŞI REZULTATE ALE CERCETĂRILOR

Au fost obținute celule fotovoltaice (CF) cu heterojoncțiunea nCdS-pInP și strat intermediar epitaxial poInP, fiind cercetate proprietățile lor electrice și fotoelectrice. Grosimile straturilor pInP și al celui frontal nCdS au variat respectiv în intervalul 2,7...6,2 – 0,9...3,6 µm în dependență de durata de depunere. S-a constatat că parametrii fotoelectrici au valorile maximale pentru grosimile de 4,5...5 µm pentru stratul poInP și de 0,9 µm pentru stratul nCdS, eficiența maxi­mală a CF cu structura n+CdS-po-p+InP fiind de 14,6% (100 mW×cm-2).PHOTOVOLTAIC CELLS WITH n+CdS-po-p+InP HETEROJUNCTION:  TEHNOLOGICAL APPLICATIONS, METHODS AND RESEARCH RESULTSPhotovoltaic cells (PVC) with nCdS-pInP heterojunction and an intermediate poInP epitaxial layer were obtained and their electrical and photoelectric properties were investigated. The thicknesses of the pInP layer and of the nCdS frontal layer varied in the range of 2.7 to 6.2 μm and 0.9 to 3.6 μm respectively, depending on the deposition time. It was found that photoelectric parameters have maximum values when the thickness of poInP layer is of 4.5 ... 5 μm and for nCdS layer is of 0.9 μm, the maximum efficiency of PCV with the structure n+CdS-po-p+InP was of 14.6% (100 mW×cm-2).</p

Aero-TiO2 Prepared on the Basis of Networks of ZnO Tetrapods

In this paper, new aeromaterials are proposed on the basis of titania thin films deposited using atomic layer deposition (ALD) on a sacrificial network of ZnO microtetrapods. The technology consists of two technological steps applied after ALD, namely, thermal treatment at different temperatures and etching of the sacrificial template. Two procedures are applied for etching, one of which is wet etching in a citric acid aqua solution, while the other one is etching in a hydride vapor phase epitaxy (HVPE) system with HCl and hydrogen chemicals. The morphology, composition, and crystal structure of the produced aeromaterials are investigated depending on the temperature of annealing and the sequence of the technological steps. The performed photoluminescence analysis suggests that the developed aeromaterials are potential candidates for photocatalytic applications

Advanced Hybrid GaN/ZnO Nanoarchitectured Microtubes for Fluorescent Micromotors Driven by UV Light

The development of functional microstructures with designed hierarchical and complex morphologies and large free active surfaces offers new potential for improvement of the pristine microstructures properties by the synergistic combination of microscopic as well as nanoscopic effects. In this contribution, dedicated methods of transmission electron microscopy (TEM) including tomography are used to characterize the complex hierarchically structured hybrid GaN/ZnO:Au microtubes containing a dense nanowire network on their interior. The presence of an epitaxially stabilized and chemically extremely stable ultrathin layer of ZnO on the inner wall of the produced GaN microtubes is evidenced. Gold nanoparticles initially trigger the catalytic growth of solid solution phase (Ga1– xZnx)(N1– xOx) nanowires into the interior space of the microtube, which are found to be terminated by AuGa-alloy nanodots coated in a shell of amorphous GaOx species after the hydride vapor phase epitaxy process. The structural characterization suggests that this hierarchical design of GaN/ZnO microtubes could offer the potential to exhibit improved photocatalytic properties, which are initially demonstrated under UV light irradiation. As a proof of concept, the produced microtubes are used as photocatalytic micromotors in the presence of hydrogen peroxide solution with luminescent properties, which are appealing for future environmental applications and active matter fundamental studies. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Aero-Ga2O3 Nanomaterial Electromagnetically Transparent from Microwaves to Terahertz for Internet of Things Applications

In this paper, fabrication of a new material is reported, the so-called Aero-Ga2O3 or Aerogallox, which represents an ultra-porous and ultra-lightweight three-dimensional architecture made from interconnected microtubes of gallium oxide with nanometer thin walls. The material is fabricated using epitaxial growth of an ultrathin layer of gallium nitride on zinc oxide microtetrapods followed by decomposition of sacrificial ZnO and oxidation of GaN which according to the results of X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS) characterizations, is transformed gradually in β-Ga2O3 with almost stoichiometric composition. The investigations show that the developed ultra-porous Aerogallox exhibits extremely low reflectivity and high transmissivity in an ultrabroadband electromagnetic spectrum ranging from X-band (8-12 GHz) to several terahertz which opens possibilities for quite new applications of gallium oxide, previously not anticipated

INFLUIENŢA TRATĂRII TERMICE ÎN AZOT SAU ÎN VID ASUPRA PROPRIETĂŢILOR STRATURILOR DE GaN CRESCUTE PE Si(111) PRIN METODA HVPE

A fost studiată influenţa tratării termice la temperaturi ridicate în azot sau în vid asupra proprietăţilor stra­turilor de GaN depuse pe siliciu prin metoda reacţiilor chimice de transport în sistemul (H2-NH3-HCl-Ga-Al), (HVPE). În spec­trele de fotoluminescenţă (FL), la 300 K, ale straturilor netratate se evidenţiază două fâşii de recombinare radiantă, cu maximele la 370 şi 555 nm. La tratarea în azot intensitatea fâşiei 370 nm creşte, iar la tratarea în vid – descreşte. Inten­sitatea benzii galbene (555 nm), la tratare în ambele medii, scade neesenţial. Se demonstrează că parametrii electrici ai straturilor pot fi, de asemenea, modificaţi prin metoda tratării termice în azot sau în vid, precum şi prin durata de tratare. The influence of high temperature annealing in nitrogen or vacuum on properties of GaN layers deposited on Si(111) by HVPE mehodThe influence of high temperature annealing in nitrogen and vacuum of GaN layers deposited by chemical reactions transport (HVPE) in (H2-NH3-HCl-Ga-Al) system on their properties was studied. In the photo­luminescence (PL) spectra at 300 K of the untreated layers two recombination radiation bands with the plats at 370 nm and 555 nm were revealed. At the layers heat treatment the intensity of the radiation band at 370 nm increases when at the intensity of the yellow band (555 nm) decreases not significantly at the treatment in the both ambiances. It was shown that the electrical parameters could as well be controlled by using heat treatment in nitrogen and vacuum and this depends on the annealing duration. </p

CELULE FOTOVOLTAICE CU HETEROJONCŢIUNEA nCdS-pInP

Au fost studiate proprietăţile electrice şi fotoelectrice ale heterojoncţiunilor nCdS-pInP cu şi fără strat epitaxial inter-mediar poInP. S-a stabilit că la polarizări directe în mecanismul de transport al curentului predomină procesele de recom-binare în regiunea de sarcină spaţială. La polarizări inverse predomină procesele de tunelare. Prezenţa stratului epitaxial poInP depus repetat măreşte ISC până la 28,2 mA·cm-2, UCD până la 0,780 V, iar eficienţa conversiei energiei până la 15% la 300 K şi iluminare 100 mW/cm2. Fotosensibilitatea CF nCdS-poInP-pInP corespunde intervalului λ=550...950 nm cu un maximum plat localizat în intervalul λ=700...850 nm.HETEROJONCTION nCdS–pInP FOTOVOLTAIC CELLSElectrical and photoelectrical properties of nCdS-pInP hetero-junctions with and without intermediate poInP epitaxial layer were studied. It was established that the current flow mechanism at direct biases is determined mainly by the recombi-nation processes in the space charge region of the junction. At the reverse biases the tunneling processes are predominant. The presence of poInP layer leads to the photo-electrical parameters enhancing of hetero-junction: short circuit current increases up to 28,2 mA·cm -2, open circuit voltage up to 0,780V and the efficiency of solar energy conversion up to 15 % (at 300 K and illumination of 100mw/cm2). The photo-sensitivity of nCdS- poInP -pInP is in the wavelength region of λ= 550-950nm with a maximum localized to λ=700-850nm.</p

Viability and proliferation of endothelial cells upon exposure to GaN nanoparticles

Nanotechnology is a rapidly growing and promising field of interest in medicine; however, nanoparticle–cell interactions are not yet fully understood. The goal of this work was to examine the interaction between endothelial cells and gallium nitride (GaN) semiconductor nanoparticles. Cellular viability, adhesion, proliferation, and uptake of nanoparticles by endothelial cells were investigated. The effect of free GaN nanoparticles versus the effect of growing endothelial cells on GaN functionalized surfaces was examined. To functionalize surfaces with GaN, GaN nanoparticles were synthesized on a sacrificial layer of zinc oxide (ZnO) nanoparticles using hydride vapor phase epitaxy. The uptake of GaN nanoparticles by porcine endothelial cells was strongly dependent upon whether they were fixed to the substrate surface or free floating in the medium. The endothelial cells grown on surfaces functionalized with GaN nanoparticles demonstrated excellent adhesion and proliferation, suggesting good biocompatibility of the nanostructured GaN