The self-catalyzed growth of InP nanowires on an aerographite substrate is demonstrated in this study by using high growth rate hydride vapor-phase epitaxy technology. Nanowires with aspect ratios higher than 200 and diameters of 0.2–2 μm were analyzed by scanning electron microscopy, transmission electron microscopy, energy-dispersive x-ray analysis, Raman spectroscopy, and photoelectrical characterization. The nanowires were found to be of constant diameter over their length, except for a well-faceted hexagonal tapered end. The novel growth process results in formation of self-catalyzed nanowires compatible with integrated circuit technology. Single-wire InP photodetectors with predominant sensitivity in the infrared spectral range have been prepared and characterized. Semiconductor nanowires gain wider application in light and gas sensors, memory and memristive devices. In this article, we describe a fast and rather simple approach of fabricating catalyst-free InP nanowires with aspect ratio of 200. Important benefits of this method are stoichiometric chemical composition and freestanding arrangement of wires on the aerographite substrate. We demonstrate the development of a robust IR single-nanowire sensor stable at 20–300 K both in the air and vacuum atmosphere, with Iph/Idark ratio in the range 4–1.7.

Straturi subțiri, de nucleație și proprii, de ZnO au fost sintetizate pe Si prin metoda hidrotermală din soluțiile compușilor zincului folosindu-se solvenții: apă, apă + etanol, apă + metanol, apă + propanol, apă + acetonă, etanol, propanol, metanol. La prepararea straturilor de nucleație s-a folosit acetatul de zinc dihidrat, Zn(CH3COO)2·2H2O. Depunerea straturilor proprii de ZnO pe structurile nucleate a avut loc prin fierberea lor în soluție apoasă de Zn(NO3)2 + KOH. În lucrare sunt date caracterizări structurale și morfologice ale straturilor buffer obținute, fiind demonstrată eficiența stratului buffer în prepararea straturilor de GaN. PHYSICAL PROPERTIES OF ZnO LAYERS PREPARED ON Si SUBSTRATES BY HYDROTHERMAL METHODThe nucleation and proper ZnO thin layers on Si substrates were synthesized by the hydrothermal method from the solutions of zinc compounds by using different solvents such as: water, water + ethanol, water + methanol, water + propanol, water + acetone, ethanol, propanol, methanol. Dehydrated zinc acetate, Zn(CH3COO)2·2H2O, was used for the preparation of ZnO nucleation layers . The deposition of the proper ZnO layers on the nucleated structures is carried out by boiling them in the Zn(NO3)2 + KOH aqueous solution. The structural and morphological characterisations of the obtained buffer layers are given in the paper. The efficiency of ZnO buffer layer used in the preparation of GaN layers is demonstrated as well.

Here, we report on a new aero-material, called aero-ZnS, representing self-organized architectures made of ZnS hollow micro-tetrapod structures with nanoscale thin walls. The fabrication process is based on the hydride vapor phase epitaxy of CdS on sacrificial micro-tetrapods of ZnO with simultaneous or subsequent transformation of CdS into ZnS and removal of the sacrificial ZnO crystals. The nanostructure of the obtained ZnS hollow micro-tetrapods exhibits the polytypic intergrowth of wurtzite- and sphalerite-type phases perpendicular to their close packed planes. The inner surface of the micro-tetrapod walls preserves oxygen sites, as demonstrated by imaging based on electron energy-loss filtering. The self-organized aero-ZnS architecture proves to be hydrophilic under tension and hydrophobic when compressed against water. Self-propelled liquid marbles assembled using ZnS hollow micro-tetrapod structures are demonstrated.

GaN layers on Silicon with ZnO intermediate layer were synthesized by using the HVPE (Hydride Vapor Phase Epitaxy) method. ZnO layers were deposited from solutions of zinc compounds in ethanol or water in two steps. At the first step a ZnO nucleation layer was deposited from a solution of zinc acetate in ethanol, at the second step a ZnO precipitate was deposited from a solution of zinc nitrate and KOH in water by boiling. On the obtained structures the GaN nucleation layers were deposited at 500 ℃ for 15 min, then GaN layers were grown at 850–970 ℃ for 30 ± 5 min. Structures were studied by using the optical and SEM microscope and XRD method. The type of conductivity of the layers was determined by using the method of thermal electromotive force measurement (TEFM). The possibility of the electrical conductivity (EC) type changing from n- to p-type for the GaN layers deposited on silicon substrates with the use of intermediate ZnO layer deposited from solutions is demonstrated for the first time.

The ZnO thin layers were grown on glass, InP and pInP-nCdS substrates from zinc acetate dissolved in water-acetic acid-methanol solution having a molarity of 0.2 M by using the spray method in the argon flow in the temperature range of (250–450) °C. The dependence of optical properties of ZnO layers on growth temperature have been investigated. The optical transmittance has values of 80–85% in the wavelength range of (200–1000) nm. The using of ZnO of the thickness of (60–80) nm as antireflective layers in nCdS-pInP structures allowed to increase the photovoltaic cell efficiency by 3%. The photosensitivity of the fabricated nZnO-pInP structures covers the wavelength region from 450 nm up to 1100 nm and allows the more efficient utilization of the incident light.

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.

In the present work, we report on development of three-dimensional flexible architectures consisting of an extremely porous three-dimensional Aerographite (AG) backbone decorated by InP micro/nanocrystallites grown by a single step hydride vapor phase epitaxy process. The systematic investigation of the hybrid materials by scanning electron microscopy demonstrates a rather uniform spatial distribution of InP crystallites without agglomeration on the surface of Aerographite microtubular structures. X-ray diffraction, transmission electron microscopy and Raman scattering analysis demonstrate that InP crystallites grown on bare Aerographite are of zincblende structure, while a preliminary functionalization of the Aerographite backbone with Au nanodots promotes the formation of crystalline In2O3 nanowires as well as gold-indium oxide core-shell nanostructures. The electromechanical properties of the hybrid AG-InP composite material are shown to be better than those of previously reported bare AG and AG-GaN networks. Robustness, elastic behavior and excellent translation of the mechanical deformation to variations in electrical conductivity highlight the prospects of AG-InP applications in tactile/strain sensors and other device structures related to flexible electronics.

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).

Straturile subţiri de ZnO au fost crescute din acetat de zinc dizolvat în apă-acid acetic-metanol cu o molaritate de 0,2 M folosind metoda pulverizării în intervalul de temperaturi (250-450)°C în flux de argon. Au fost cercetate proprietăţile optice şi electrice ale acestor straturi în dependenţă de temperatura de creștere. Transmitanţa în diapazonul de lungimi de undă (300-1000) nm are valori de 80-85%. Rezistenţa specifică a straturilor subțiri de ZnO crescute la 450°C după tratarea termică în vid şi hidrogen la 450°C timp de o oră se micșorează de la 33 •cm până la 0,028 •cm. Recombinarea radiantă în straturile de ZnO este însoțită de tranziții pe niveluri adânci și de tranziții bandă-bandă la interacțiunea purtătorilor de sarcină cu fononii de tip LO. Cuvinte-cheie: oxid de zinc, transmitanță, pulverizare.

Polycrystalline undoped and Al-doped ZnO thin films were deposited by spray pyrolysis using oxygen and argon atmospheres. The influence of postdeposition vacuum annealing on the structure, morphology and optical properties was studied by X-ray diffraction, atomic force microscopy and UV-VIS spectroscopy. The thermal vacuum annealing induces structural and morphological changes, especially in Al-doped ZnO thin films synthetized in oxygen atmosphere. Further on, the electrical conductivity in dependence of the nature of gas atmosphere and Al concentration is discussed.

Prin metoda reacțiilor chimice de transport HVPE (Hydride Vapor Phase Epitaxy) in sistemul (H 2 -NH 3 -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 inaltă. Compoziția in 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 in 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 in straturi are loc in urma descompunerii cuarțului, din care este confecționat reactorul, la temperaturi ridicate. S-a constatat că incorporarea galiului in 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 inlăturate 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 METHOD Using 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.

Au fost studiate caracteristicile capacitate-tensiune-conductabilitate-frecvenţă ale homo­joncţi­uni­lor n+-p°-p+InP cu şi fără strat frontal n+CdS obţinute cu aplicarea tehnologiilor din faza gazoasă în sistemul In-PCl3-H2 şi în volum cvasiînchis. S-a stabilit că distribuirea impurităţilor în regiunea sarcinii de baraj în astfel de joncţiuni este cu gradient liniar, iar la frecvenţele de 7…10 MHz impendanţa structurii este determinată de rezistenţa inductivă. Concentraţia stărilor super­ficiale pentru structurile n+-p°-p+InP cu strat frontal de n+CdS este cu un ordin mai mică decât fără acest strat, ceea ce va spori eficienţa CF obţinute în baza lor.CAPACITANCE AND ELECTRICAL CONDUCTIVITY STUDIES OF P-INP JUNCTIONSThe capacitance –voltage-conductivity-frequency dependencies of n+-po-p+InP with and without n+CdS frontal layer, obtained by using of gaseous phase epitaxial technology in a In-PCl3-H2 system and deposition in a quasi-closed volume, were studied. It was established that the impurity distribution in the space charge region of such junctions is of a linear gradient, and at the frequencies of 7…10 MHz the structure impedance is determined by the inductance resistance. The surface state concentration in n+-po-p+InP structures with the n+CdS frontal layer is by an order of magnitude lower than in the same structures without it, which can enhance the efficiency of solar cells based on them.

Thin layers of GaN, and AlGaN were synthesized on Silicon substrates by chemical transport reactions method in the system (H2-NH3-HCl-Al-Ga).The composition of surface layers was studied by X-ray Photoelectron Spectroscopy Method. Besides Nitrogen, Aluminum, and Gallium, there were found also other elements - Carbon, and Oxygen in the atomic composition of layers. It was found a lower concentration of oxygen atoms in the composition of GaN layers deposited at relatively lower temperatures. It is assumed that the presence of Oxygen in the composition of layers is partly due to the decomposition of quartz glass, which the reactor is made from at high temperatures. It was found that atomic concentration of Gallium in AlGaN layers is much less than the Aluminum concentration, despite of the fact that the concentrations of Gallium and Aluminum precursors in the gaseous flow at the entrance in the synthesis zone were in equimolecular ratio. This demonstrates that the rate of chemical reactions of the ammonia with gaseous components of the Aluminum is significantly greater than with that of the Gallium. Therefore, the latter are removed by the gas stream from the growth zone.

Au fost obţinute homojoncţiuni n-pInP cu strat intermediar p-InP crescut repetat prin metoda HVPE cu sau fără strat frontal nCdS şi au fost cercetate proprietăţile electrice şi fotoelectrice ale acestora. S-a constatat că depunerea stratului intermediar măreşte fotosensibilitatea homostructurilor cu 15…20%. Eficienţa energetică a CF cu structura n+CdS-n+InP-p-InP-p+InP constituie 13,5% pentru fluxul luminos incident de 100 mW×cm-2. Eficienţa CF cu heterostructura nCdS-pInP şi cu strat intermediar similar creşte cu 27%, în comparaţie cu CF cu homostructura n-p--pInP şi cu strat frontal nCdS, având valoarea de 17,3%. Se conturează posibilitatea reală de mărire a eficienţei CF de acest tip.FOTOVOLTAIC CELLS WITH HOMOJUNCTIONS IN InP: REZULTS AND COMPARISONSElectrical and photoelectrical properties of InP p-n homojunctions with an intermediate p-InP layer repeatedly grown by HVPE method, with and without frontal nCdS layer were produced and studied. It was found that the deposition of this intermediate p-InP layer increases the cells photosensitivity by 15 ... 20%. The solar energy conversion efficiency of photovoltaic cell (PC) with n+CdS-n+InP-p-InP-p+InP structure is 13.5% at the illumination of 100 mW.cm-2. The efficiency of the PC based on nCdS-pInP heterostructure and an analogic intermediate layer increases to 27% compared with the PC based on n-p--pInP homostructure having a frontal nCdS layer has an efficiency of 17.3%. The possibility of increasing of the efficiency of this PC type is formulated.

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.

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.

This report concerns the automatic control system based on the programmable controller TRM-151-01 of the temperature of semiconductor alloying with zinc and tellurium. The goal of the research is the industrial modernization of the epitaxial growth technology of semiconductor materials in the form of thin multiple layers (inclusively nano-dimensions) with variable values of the electric conductibility.