Browsing by Author "Gorceac, Leonid"

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ABOUT THE EDGE LUMINESCENCE OF CADMIUM SULPHIDE THIN LAYERS GROWN ON MOLYBDENUM
(Institute of Electrical and Electronics Engineers, 1995-11-11) Raevschi, Simion; Gorceac, Leonid; Coval, Andrei; Chetruș, Petru
CdS layers on to molybdenum were synthesized from separate elements in an open flowing hydrogen set. The surface micromorphology and some electrical and photoluminescent properties were investigated. The nature of layers edge photoluminescence peaks are discussed in the frames of the excitated exciton model.
AERO-ZNS ARCHITECTURES WITH DUAL HYDROPHILIC–HYDROPHOBIC PROPERTIES FOR MICROFLUIDIC APPLICATIONS
(2020) Pleșco, Irina; Braniște, Tudor; Wolff, Niklas; Gorceac, Leonid; Duppel, Viola; Cinic, Boris; Mishra, Yogendra Kumar; Sarua, Andrei; Adelung, Rainer; Kienle, Lorenz; Tighineanu, Ion
Here, we report on a new aero-material, called aero-ZnS, representing self-organized architectures made of ZnS hollow micro-tetrapod struc- tures 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.
AUTOMATION CONTROL SYSTEM OF THE ALLOYING PROCESS OF GALLIUM ARSENIDE LAYERS GROWTH BY EPITAXIAL TECHNOLOGY
(Institute of Electrical and Electronics Engineers Inc., 2012-10-20) Baranov, Simion; Cojuhari, Irina; Izvoreanu, Bartolomeu; Gorceac, Leonid
This paper proposes to control the thermal alloying process of GaAs epilayers growth by transport reaction in Ga- AsCl 3-H2 system. The thermal alloying process is controlled by using the universal two-channel programmable PID-controller TRM151, which permits automatic control of complicated objects with high precision. The thermal process was identified using the parametric model ARX (Auto-Regressive eXogenous) from System Identification Toolbox from MATLAB. The experimental technologist’s program contains steps of p +- po –n + photovoltaic structures achievement with damper layer on p-GaAs substrate. There is a possibility to obtain multiple periodical epitaxial layers structures with different dimensions and electro-physical properties, including nano-dimension structures, changing different steps of production. The tuning controller was performed using the maximal stability degree method. This control system minimizes the new technologies elaboration terms, accelerates the implementation of the elaborated technology in industry by reducing production costs, improving the product quality and its market competitiveness.
THE CARACTERIZATION OF THE CdS-BASED SOLAR CELL HETEROJUNCTIONS
(Institute of Electrical and Electronics Engineers Inc., 2010-10-11) Potlog, Tamara; Botnariuc, Vasile; Gorceac, Leonid; Spalatu, Nicolae; Maticiuc, Natalia; Raevschi, Simion
The CdS-based solar cell heterojunctions (HJ) have been obtained by growth of CdS at relatively lower temperature using the close space sublimation method(CSS). Investigation of the photovoltaic characteristics shows an efficiency of about 12 % for InP/CdS and 9.6 % for CdS/CdTe solar cell HJ. The analysis of the forward dark current-voltage and the capacitance-voltage characteristics indicate a tunnelling recombination current which flows through states near or at the interfaces of a thermal energy of about 0.62 eV for CdS/CdTe and 0.42 eV for InP/CdS solar cell heterojunctions. The solar energy conversion efficiency is influenced by the interface states through the open circuit voltage and the fill factor.
CdS NANOMETRIC LAYERS GROWN ON SnO2 COATED GLASS SUBSTRATES FOR PHOTOVOLTAIC DEVICES
(2012) Botnariuc, Vasile; Gorceac, Leonid; Coval, Andrei; Chetruș, Petru; Cinic, Boris; Raevschii, Simion; Micli, Valdec
CdS layer thickness decreases at high substrate temperatures due to the fact that a part of CdCl2/(NH2)2 CS aqueous solution evaporates without reaching the substrate surface. CdS layers deposited at the substrate temperature from 250oC to 450oC are growing with a deficit of sulfur. CdS layers with better stoichiometry were grown in the conditions when in the solutions, used for CdS layers growing, there is an excess of thiourea (CdCl2/ TU =1:2). The high charge carrier concentration of 1020cm-3 in CdS layers grown on glass substrates coated with SnO2 layer is related to Sn doping of the layers from SnO2 layer.
CELULE FOTOVOLTAICE CU HETEROJONCȚIUNEA n+CdS-p o -p + InP: APLICĂRI TEHNOLOGICE, METODE ŞI REZULTATE ALE CERCETĂRILOR
(CEP USM, 2018) Botnariuc, Vasile; Gagara, Ludmila; Gorceac, Leonid; Cinic, Boris; Covali, Andrei; Raevschi, Simion; Rotaru, Cornel
Au fost obținute celule fotovoltaice (CF) cu heterojoncțiunea nCdS-pInP și strat intermediar epitaxial po InP, 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 po InP și de 0,9 µm pentru stratul nCdS, eficiența maximală a CF cu structura n+CdS-p o -p + InP fiind de 14,6% (100 mWcm-2).
CELULE FOTOVOLTAICE CU HETEROJONCŢIUNEA nCdS-pInP
(CEP USM, 2015) Botnariuc, Vasile; Gașin, Petru; Gorceac, Leonid; Inculeț, Ion; Cinic, Boris; Covali, Andrei; Raevschi, Simion
Au fost studiate proprietăţile electrice şi fotoelectrice ale heterojoncţiunilor nCdS-pInP cu şi fărăstrat epitaxial intermediar poInP. S-a stabilit că la polarizări directe în mecanismul de transport al curentului predominăprocesele de recombinare în regiunea de sarcină spaţială. La polarizări inverse predominăprocesele de tunelare. Prezenţa stratului epitaxial poInP depus repetat măreşte ISCpânăla 28,2 mA•cm-2, UCDpânăla 0,780 V, iar eficienţa conversiei energiei pânăla 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.
CELULE FOTOVOLTAICE CU HOMOJONCŢIU.NE DIN InP: REZULTATE ŞI COMPARĂRI
(CEP USM, 2016) Botnariuc, Vasile; Gașin, Petru; Gorceac, Leonid; Cinic, Boris; Coval, Andrei; Raevschi, Simion
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 mWcm-2. Eficienţa CF cu heterostructura nCdS-pInPşi cu strat intermediar similar creşte cu 27%, în comparaţie cu CFcu 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.
CELULE SOLARE CU HOMOJONCIUNE DIN FOSFURĂ DE INDIU
(CEP USM, 2013) Botnariuc, Vasile; Gorceac, Leonid; Cinic, Boris; Coval, Andrei; Inculeț, Ion; Raevschi, Simion
Homojoncţiunea p+-p--n+InPcu şi fără strat frontal nCdS a fost obţinută aplicând metoda de epitaxie din faza gazoasă în sistemul In -PCl3-H2(p-InP, n+InP) şi metoda de volum cvasiînchis (nCdS). La studierea proprietăţilor electrice şi fotoelectrice ale acestor structuri s-a constatat că fotosensibilitatea a crescutcu două ordine,iar eficienţa CS este de 12% pentru homo structura cu strat frontal nCdS. Aceasta se datorează micşorării recombinării purtătorilor de sarcină minoritari la suprafaţă şi particularităţilor proprietăţilor electrice şi fotoelectrice ale acestor structuri.
CERCETAREA CAPACITĂȚII ȘI CONDUCTIBILITĂȚII ELECTRICE ALE JONCȚIUNILOR DIN P-INP
(CEP USM, 2017) Botnariuc, Vasile; Gagara, Ludmila; Gorceac, Leonid; Cinic, Boris; Covali, Andrei; Raevschi, Simion; Rotaru, Cornel
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 ceva spori eficienţa CF obţinute în baza lor.
CERCETAREA CELULELOR SOLARE CU HETEROJONCŢIUNEA nCdS-pInP
(CEP USM, 2009) Gorceac, Leonid; Botnariuc, Vasile; Raevschi, Simion; Coval, Andrei; Chitoroagă, Andrei
Photoelectrical dependencies of nCdS-pInP solar cells, as a function of electro physical parameters, crystallographic orientation of InP substrate and of the deposition duration of the nCdS epitaxial for layer are presented. It was established that the maximum value of the efficiency of solar energy into electrical one is obtained for the holes concentration in the substrate of 2·1016 cm-3, crystallographic orientation (100) and layer growth duration of 25 min. The hetero structure parameters influencing the named dependencies are determined.
CERCETĂRI XRD ȘI XPS ALE STRATURILOR DE AlN, AlGaN, GaN DEPUSE PE SILICIU PRIN METODA HVPE
(CEP USM, 2018) Raevschi, Simion; Spalatu, Nicolae; Botnariuc, Vasile; Gorceac, Leonid; Potlog, Tamara; Dobromir, Marius
Prin metoda reacțiilor chimice de transport HVPE (Hydride Vapor Phase Epitaxy) in sistemul (H2-NH3-HCl-Al-GaSi) 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.
DISPOZITIVE DIN FOSFURĂ DE INDIU BAZATE PE EFECTUL FOTOVOLTAIC
(CEP USM, 2021) Botnariuc, Vasile; Gorceac, Leonid; Coval, Andrei; Vatavu, Sergiu; Cinic, Boris; Rotaru, Corneliu; Raevschi, Simion
Homo- și heterojoncțiunile din p - InP și n - CdS au fost confecționate aplicând metoda epitaxiei din faza gazoasă în volum deschis, în sistem de cloruri, metoda HVPE (Hydride Vapour Phase Epitaxy) și tehnologia în volum cvasiînchis, în hidrogen. S-a stabilit că eficiența celulelor fotovoltaice pe bază de heterojoncțiuni n+CdS-p-p+InP cu suprafața fotoactivă de 3 cm2 și pe homojoncțiuni n+- p- p+InP (1 cm2) constituie 12% și,respectiv, 7,3% în condiții de iluminare standard, AM1 (1000 Wm-2). Eficiența cuantică externă maximală constituie 75-80% pentru heterojoncțiunea n+CdS - p- p+ InP și 70% pentru homojoncțiunea n+-p-p+InP în intervalul (600-900) nm al spectrului electromagnetic. Fotosensibilitatea absolută maximă de 0,51 A/W este caracteristică pentru heterojoncțiunea n+CdS - p- p+InP cu strat epitaxial intermediar(p = 6,51016 cm-3). Astfel de heterojoncțiuni pot fi utilizate pentru elaborarea fotodetectorilor în intervalul VIS.
EFFECT OF CARRIER GAS AND VACUUM ANNEALING ON THE PHYSICAL PROPERTIES OF ZnO THIN FILMS DOPED WITH GALLIUM BY CHEMICAL SPRAY PYROLYSIS
(Editura "Tehnica-UTM", 2018-05-24) Potlog, Tamara; Lungu, Ion; Botnariuc, Vasile; Raevschi, Simion; Worasawat, Suchada; Mimura, Hidenori; Gorceac, Leonid
Structural, optical and electrical properties of zinc oxide thin films doped with 2% Ga, annealed in the vacuum at the same temperature and obtained onto glass substrates by the chemical spray pyrolysis method in the different gas atmospheres were investigated by X-ray Diffraction (XRD), UV-VIS spectrophotometry and Hall measurements, respectively. XRD studies revealed that all films were polycrystalline in nature, with a hexagonal wurtzite crystal structure and a predominant (002) c-axis orientation. All ZnO:Ga thin films had higher than 80 % transmittances in the visible region. Doping with 2% Ga led to a decrease in the optical band gap indifferent of the nature of the carrier gas. The synthesis of ZnO thin films with 2% Ga doping and annealing in the same conditions in Ar and O2 atmospheres led to the lower conductivity with electron concentration of 1016 cm−3.
EVOLUAREA PARTICULELOR DISPERSATE DE AlN DEPUSE PE Si PRIN METODA HVPE LA ETAPA DE FORMARE A STRATULUI CONTINUU
(CEP USM, 2011) Raevschi, Simion; Kompan, Mihail; Zhilyaev, Yurii; Gorceac, Leonid; Botnariuc, Vasile
Evolution of growth of the disperse particles of AlN which has been grown up on substrates of silicon during formation of a continuous layer are studies by AFM (Atomic Force Microscopy ) method. Layers have been grown up by HVPE (Hydride Vapor Phase Epitaxy) method at 1100o C. It is established: a) nunucleation occurs according to three dimensional model; b) layers are formed of two categories of disperse particles; c) growth rate of categories differ; d) at an initial stage of growth there is a latent period of time when superficial concentration of disperse particles remains to a constant.
FABRICATION AND CHARACTERIZATION OF FLEXIBLE COMPOSITE MATERIAL BASED ON AEROGRAPHITE/INP MICRO-ANOSTRUCTURES
(UTM, 2017) Gorceac, Leonid
The goal of this work is to extend the class of flexible hybrid nanomaterials based on aerographite scaffolds. For this purpose,we developed the technological conditions for the deposition of InP:Zn micro-and nanostructures on both as-grown samples and specimens preliminarily decorated by Au dots. InP·Zn deposition was realized by using Hydride Vapor Phase Epitaxy (HVPE), while the gold dots were deposited by sputtering with subsequent annealing of the samples. For the characterization of morphology and chemical composition of the specimens, we used transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX).
FOTODETECTOR PE HETEROJONCȚIUNE DIN FOSFURĂ DE INDIU
(CEP USM, 2020) Gorceac, Leonid; Botnariuc, Vasile; Coval, Andrei; Vatavu, Sergiu; Cinic, Boris; Raevschi, Simion; Rotaru, Corneliu
GROWTH OF P-GAN ON SILICON SUBSTRATES WITH ZNO BUFFER LAYERS
(Springer Nature, 2020) Raevschi, Simion; Gorceac, Leonid; Botnariuc, Vasile; Branişte, Tudor
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.
HIERARCHICAL AEROGRAPHITE 3D FLEXIBLE NETWORKS HYBRIDIZED BY InP MICRO/NANOSTRUCTURES FOR STRAIN SENSOR APPLICATIONS
(Springer Nature, 2018) Gorceac, Leonid; Plesco, Irina; Tiginyanu, Ion; Cinici, Boris; Ursaki, Veaceslav
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 In 2 O 3 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
HIGH TEMPERATURE ULTRA-FAST GALLIUM ARSENIDE RECTIFIER DEVICES
(Institute of Electrical and Electronics Engineers Inc., 2012-10-20) Baranov, Simion; Gorceac, Leonid; Cheibaș, Victor
The report is related to the high temperature electronics field. The industrial developed country practice demonstrates that up to 70% of the fabricated electrical energy passes through semiconductor converters. Only in the field of electrical drive, which uses about 50% from the produced electrical energy, passing to the frequency converter of the asynchronous drives speed control, brings an energy economy up to 25%. In the electrical transport with the energy braking recovering the economy is more than 30%. The present elaboration is foreseeing the improvement of the technological production route of gallium arsenide (GaAs) power semiconductor devices (PSD), by introducing some innovative technological processes as: (1) GaAs epitaxial technology in the Ga-AsCl 3-H2 system; (2) epitaxial structures divided into crystals by chemical method; (3) GaAs p-n junction passivation by own oxide (Ga2 O3) precipitate on the divided surface of the crystal. The goal of the project is increasing manufacturing efficiency (ME) at the GaAs power devices with more than 600 V of voltage fabrication. The proposed improvements are increasing ME with 40% and are expanding the blocking voltage interval up to 1000 V. As a result a new product was elaborated and proposed to the manufacturing– the ultra-fast current converter with 80 ns of recovery time, stable at high temperature (200 oC) and 4.5 kV of blocking voltage, that outrun the characteristics of commercial product ESJC30-05(0.3 s, 110 oC).