共查询到20条相似文献,搜索用时 31 毫秒
1.
H. Ohyama K. Takakura K. Uemura K. Shigaki T. Kudou T. Matsumoto M. Arai S. Kuboyama C. Kamezawa E. Simoen C. Claeys 《Superlattices and Microstructures》2006,40(4-6):632
The impact of radiation source dependence on the device performance degradation of 4H-SiC MESFETs (Metal Schottky Field Effect Transistors), which have been irradiated at room temperature with 2 MeV electrons and 20 MeV protons, is studied. No performance degradation is observed by 1×1015 e/cm2 and 5×1011 p/cm2, while a slight increase of the linear drain current together with a decrease of the threshold voltage are noticed above higher fluence. The damage coefficient for protons is about three orders of magnitude larger than that for electrons. The radiation source dependence of the device performance degradation is attributed to the difference of mass and the possibility of nuclear collision for the formation of lattice defects. Based on thermal annealing results of electron-irradiated MESFETs, it is found that the recovery of the drain current characteristics principally takes place from 100 C, and that the drain current recovers to the pre-rad value after 200 C annealing. On the other hand, capacitance and induced deep levels do not recover by 200 C annealing. It is concluded that the degradation of the drain current is mainly sensitive to the radiation-induced decrease of the Schottky barrier height at the gate contact. 相似文献
2.
The temperature dependence of the minority carrier diffusion length and lifetime in bulk n-type ZnO was studied using Electron-Beam-Induced Current (EBIC) and cathodoluminescence (CL) techniques. The diffusion length was observed to increase exponentially over the temperature range from 25 to 125 C, yielding an activation energy of 45 ± 2 meV. A concomitant decrease of the cathodoluminescence intensity for the near-band-edge transition was also observed. The activation energy determined by optical measurements was 58 ± 7 meV. The larger minority carrier diffusion length and smaller luminescence intensity are attributed to the increased lifetime of non-equilibrium holes in the valence band at elevated temperatures. Carrier trapping on Li-related levels with activation energy 283 ± 9 meV is also addressed. 相似文献
3.
I.S. Roqan K. Lorenz K.P. ODonnell C. Trager-Cowan R.W.
Martin I.M. Watson E. Alves 《Superlattices and Microstructures》2006,40(4-6):445
Room temperature cathodoluminescence (RTCL) was obtained from Tm implanted AlxGa1−xN with different AlN contents (in the range 0≤x≤0.2) and from implanted InxAl1−xN with different InN contents (x=0.13 and 0.19) close to the lattice match with GaN. The Tm3+ emission spectrum depends critically on the host material. The blue emission from AlxGa1−xN:Tm peaks in intensity for an AlN content of x0.11. The emission is enhanced by up to a factor of 50 times with an increase of annealing temperature from 1000 to 1300 C. The blue emission from In0.13Al0.87N:Tm, annealed at 1200 C, is more than ten times stronger than that from AlxGa1−xN:Tm, x≤0.2. However, the intensity decreases significantly as the InN fraction increases from 0.13 to 0.19. 相似文献
4.
Dabin Lin Zhenrong Li Shujun Zhang Zhuo Xu Xi Yao 《Solid State Communications》2009,149(39-40):1646-1649
(K0.5Na0.5)NbO3 (KNN) single crystals were grown using a high temperature flux method. The dielectric permittivity was measured as a function of temperature for [001]-oriented KNN single crystals. The ferroelectric phase transition temperatures, including the rhombohedral–orthorhombic TR−O, orthorhombic–tetragonal TO−T and tetragonal–cubic TC were found to be located at −149 C, 205 C and 393 C, respectively. The domain structure evolution with an increasing temperature in [001]-oriented KNN single crystal was observed using polarized light microscopy (PLM), where three distinguished changes of the domain structures were found to occur at −150 C, 213 C and 400 C, corresponding to the three phase transition temperatures. 相似文献
5.
Min-Woo Ha Seung-Chul Lee Soo-Seong Kim Chong-Man Yun Min-Koo Han 《Superlattices and Microstructures》2006,40(4-6):562
A new AlGaN/GaN high electron mobility transistor (HEMT) employing Ni/Au Schottky gate oxidation and benzocyclobutene (BCB) passivation is fabricated in order to increase a breakdown voltage and forward drain current. The Ni/Au Schottky gate metal with a thickness of 50/300 nm is oxidized under oxygen ambient at 500 C and the highly resistive NiO is formed at the gate edge. The leakage current of AlGaN/GaN HEMTs is decreased from 4.94 μA to 3.34 nA due to the formation of NiO. The BCB, which has a low dielectric constant, successfully passivates AlGaN/GaN HEMTs by suppressing electron injection into surface states. The BCB passivation layer has a low capacitance, so BCB passivation increases the switching speed of AlGaN/GaN HEMTs compared with silicon nitride passivation, which has a high dielectric constant. The forward drain current of a BCB-passivated device is 199 mA /mm, while that of an unpassivated device is 172 mA /mm due to the increase in two-dimensional electron gas (2DEG) charge. 相似文献
6.
V. Donderis M.A. Hernndez-Fenollosa L.C. Damonte B. Marí J. Cembrero 《Superlattices and Microstructures》2007,42(1-6):461
Nanocolumnar ZnO films were prepared by electrodeposition (ED) on a glass substrate covered with a conductive layer of thin oxide doped with fluorine (FTO). After deposition the samples were annealed in oxidizing or reducing atmosphere, at temperatures between 100 to 500 C, in order to follow the evolution of optical properties and morphology. The optical properties of these films were studied by means of photoluminescence spectroscopy (PL) and the morphology by scanning electron microscopy (SEM). Films annealed at 300 C exhibit a higher ultraviolet emission peak, originating from exciton transitions. A green band related to deep-level emission centered at 500 nm, shows a drastic increase at 500 C. These results are independent of the annealing atmosphere. An increase of coalescence is also observed after annealing at 500 C. These results are explained taking into account the contribution of different point defects. 相似文献
7.
Effects of annealing temperature on morphologies and optical properties of ZnO nanostructures 总被引:1,自引:0,他引:1
Jinghai Yang Ming Gao Yongjun Zhang Lili Yang Jihui Lang Dandan Wang Huilian Liu Yanqing Liu Yaxin Wang Hougang Fan 《Superlattices and Microstructures》2008,44(2):137-142
The effects of annealing temperature on the morphologies and optical properties of ZnO nanostructures synthesized by sol–gel method were investigated in detail. The SEM results showed that uniform ZnO nanorods formed at 900 C. The PL results showed an ultraviolet emission peak and a relatively broad visible light emission peak for all ZnO nanostructures sintered at different temperature. The increase of the crystal size and decrease of tensile stress resulted in the UV emission peak shifted from 386 to 389 nm when annealing temperature rose from 850 to 1000 C. The growth mechanism of the ZnO nanorods is discussed. 相似文献
8.
T. Dedova M. Krunks M. Grossberg O. Volobujeva I. Oja Acik 《Superlattices and Microstructures》2007,42(1-6):444
ZnO layers were deposited by chemical spray pyrolysis (CSP) using zinc chloride aqueous solutions onto indium tin oxide (ITO) glass substrates at growth temperatures in the region of 400–580 C. The layers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and low-temperature () photoluminescence (PL) measurements. The flat film of ZnO obtained at 400 C evolves to a structured layer by raising the temperature up to 500 C. Deposition around 550 C and above results in a layer comprising well-shaped hexagonal ZnO nanorods with diameter of 100–150 nm and length of up to 1 micron. XRD shows strong c-axis orientation of ZnO being in accordance with the SEM study. Deposition of nanorods was successful using ITO with grain size around 100 nm, whereas on fine-grained ITO (grain size < 50 nm) with smooth surface fat crystals with diameter up to 400 nm and length of about 300 nm were formed. Sharp near band edge (NBE) emission peaks centered at 3.360 and 3.356 eV dominated the PL spectra of ZnO at , originating from the exciton transition bound to neutral donors. PL and XRD results suggest that ZnO rods prepared by spray pyrolysis are of high optical and crystalline quality. 相似文献
9.
Fabrication and properties of ZnO:Cu and ZnO:Ag thin films 总被引:1,自引:0,他引:1
V.S. Khomchenko T.G. Kryshtab A.K. Savin L.V. Zavyalova N.N. Roshchina V.E. Rodionov O.S. Lytvyn V.I. Kushnirenko V.B. Khachatryan J.A. Andraca-Adame 《Superlattices and Microstructures》2007,42(1-6):94
Thin films of ZnS and ZnO:Cu were grown by an original metal–organic chemical vapour deposition (MOCVD) method under atmospheric pressure onto glass substrates. Pulse photo-assisted rapid thermal annealing of ZnO:Cu films in ambient air and at the temperature of 700–800 C was used instead of the common long-duration annealing in a vacuum furnace. ZnO:Ag thin films were prepared by oxidation and Ag doping of ZnS films. At first a closed space sublimation technique was used for Ag doping of ZnO films. The oxidation and Ag doping were carried out by a new non-vacuum method at a temperature >500 C. Crystal quality and optical properties were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), and photoluminescence (PL). It was found that the doped films have a higher degree of crystallinity than undoped films. The spectra of as-deposited ZnO:Cu films contained the bands typical for copper, i.e. the green band and the yellow band. After pulse annealing at high temperature the 410 and 435 nm photoluminescent peaks were observed. This allows changing of the emission colour from blue to white. Flat-top ZnO:Ag films were obtained with the surface roughness of 7 nm. These samples show a strong ultraviolet (UV) emission at room temperature. The 385 nm photoluminescent peak obtained is assigned to the exciton–exciton emission. 相似文献
10.
Wen-Chang Huang Shui-Hsiang Su Yu-Kuei Hsu Chih-Chia Wang Chen-Shiung Chang 《Superlattices and Microstructures》2006,40(4-6):644
A new Schottky diode, Al/p-GaSe, was presented in this study. It shows an effective barrier height of 0.96 eV with an ideality factor of 1.24 over five decades and a reverse leakage current density of 4.12×10−7 A/cm2 at −2 V after rapid thermal annealing at 400 C for 30 s. The generation–recombination effect of the Schottky diode was decreased as the annealing temperature was increased. The formation of Al1.33Se2 was observed by X-ray diffraction analysis after the diode was annealed at 400 C for 30 s. Owing to the grains’ growth, the surface morphology of the 400 C-annealed diode was rougher than that of the unannealed diode, which was observed both by the AFM and the SEM analysis. 相似文献
11.
The effect on the annealing temperature of Li doped ZnO thin film for a film bulk acoustic resonator
We investigated the material and electrical properties of Li doped ZnO thin film (ZLO) with variation of the annealing temperature. In the 500 C sample, ZLO film showed well defined (002) c-axis orientation and a full width half-maximum property of 0.25. The electrical properties of ZLO thin films showed the excellent specific resistance of 1.5×1011 Ω cm. Finally, the frequency characteristics of the ZLO thin film FBAR, according to the annealing temperature, showed improvement of the return loss from 24.48 to 30.02 dB at a resonant frequency of 1.17 GHz. 相似文献
12.
G. Kenanakis M. Androulidaki E. Koudoumas C. Savvakis N. Katsarakis 《Superlattices and Microstructures》2007,42(1-6):473
Zinc oxide nanostructured films were grown by the aqueous chemical growth technique using equimolar aqueous solutions of zinc nitrate and hexamethylenetetramine as precursors. Silicon(100) and glass substrates were placed in Pyrex glass bottles with polypropylene autoclavable screw caps containing the precursors described above, and heated at 95 C for several hours. X-ray diffraction 2θ/θ scans showed that the only crystallographic phase present was the hexagonal wurtzite structure. Scanning electron microscopy showed the formation of flowerlike ZnO nanostructures, consisting of hexagonal nanorods with a diameter of a few hundred nanometers. The photoluminescence spectra of the ZnO nanostructures were recorded at 18–295 K using a cw He–Cd laser (325 nm) and a pulsed laser (266 nm). The ZnO nanostructures exhibit an ultraviolet emission band centered at 3.192 eV in the vicinity of the band edge, which is attributed to the well-known excitonic transition in ZnO. 相似文献
13.
A.A. Evtukh V.G. Litovchenko M.O. Semenenko V.A. Karpyna G.V. Lashkarev V.I. Lazorenko V.D. Khranovskyy L.I. Kopylova I.Yu. Okun Yu.P. Piryatinskyy 《Superlattices and Microstructures》2007,42(1-6):451
ZnO microcrystals and nanocrystals were grown on silicon substrates by condensation from vapour phase. Nanostructured ZnO films were deposited by plasma enhanced metal organic chemical vapour deposition (PEMOCVD). The parameters of field emission, namely form-factor β and work function , were calculated for ZnO structures by the help of the Fowler–Nordheim equation. The work functions from ZnO nanostructured films were evaluated by a comparison method. The density of emission current from ZnO nanostructures reaches 0.6 mA/cm2 at electric force F=2.1105 V/cm. During repeatable measurements β changes from 5.8104 to 2.3106 cm−1, indicating improvement of field emission. Obtained values of work functions were 3.7±0.37 eV and 2.9–3.2 eV for ZnO nanostructures and ZnO films respectively. 相似文献
14.
T. Kryshtab V.S. Khomchenko J.A. Andraca-Adame V.E. Rodionov V.B. Khachatryan Yu.A. Tzyrkunov 《Superlattices and Microstructures》2006,40(4-6):651
For the fabrication of green and blue emitting ZnS structures the elements of I, III, and VII groups (Cu, Al, Ga, Cl) are used as dopants. The influence of type of impurity, doping technique, and type of substrate on crystalline structure and surface morphology together with luminescent properties was investigated. The doping of thin films was realized during the growth process and/or post-deposition thermal treatment. ZnS thin films were deposited by physical (EBE) and chemical (MOCVD) methods onto glass or ceramic (BaTiO3) substrates. Closed spaced evaporation and thermodiffusion methods were used for the post-deposition doping of ZnS films. X-ray diffraction (XRD) techniques, atomic force microscopy (AFM), and measurements of photoluminescent (PL) spectra were used for the investigations. It was shown that the doping by the elements of I (Cu) and III (Al, Ga) groups does not change the crystal structure during the thermal treatment up to 1000 C, whereas simultaneous use of the elements of I (Cu) and VII (Cl) groups leads to decrease of the phase transition temperature to 800 C. The presence of impurities in the growth process leads to a grain size increase. At post-deposition treatment Ga and Cl act as activators of recrystallization process. The transition of ZnS sphalerite lattice to wurtzite one leads to the displacement of the blue emission band position towards the short-wavelength range by 10 nm. 相似文献
15.
H. Vang M. Lazar P. Brosselard C. Raynaud P. Cremillieu J.-L. Leclercq J.-M. Bluet S. Scharnholz D. Planson 《Superlattices and Microstructures》2006,40(4-6):626
Investigations on Ni/Al alloys to form ohmic contacts to p-type 4H-SiC are presented in this paper. Different ratios of Ni/Al were examined. Rapid thermal annealing was performed in argon atmosphere at 400 C for 1 min, followed by an annealing at 1000 C for 2 min. In order to extract the specific contact resistance, TLM test structures were fabricated. A specific contact resistance of 3×10−5 Ω cm2 was obtained reproducibly on Al2+ implanted p-type layers, having a doping concentration of 1×1019 cm−3. The lowest specific contact resistance value measured amounts to 8×10−6 Ω cm2. 相似文献
16.
J. Dumont B.J. Kowalski M. Pietrzyk T. Seldrum L. Houssiau B. Douhard I. Grzegory S. Porowski R. Sporken 《Superlattices and Microstructures》2006,40(4-6):607
The interaction of Mn thin films on atomically flat GaN() has been investigated by Scanning Tunneling Microscopy (STM) and Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS). GaN surfaces prepared by repeated sputtering/annealing cycles show various reconstructions but essentially the 6×6 one. A high density of small islands (height 0.6 nm, diameter 5 nm) nucleates upon deposition of 0.3 ML Mn. Upon annealing at 575 C, these islands coalesce into larger islands (height 4 nm, diameter 50 nm) between which the GaN surface is visible. Atomically resolved STM images between the islands show the (3×3) reconstruction of GaN. Annealing the sample further to 675 C leads to the restoration of a bare GaN surface. ToF-SIMS reveals that Mn diffused into the bulk of the sample. 相似文献
17.
K. Grasza E. usakowska P. Skupinski H. Sakowska A. Mycielski 《Superlattices and Microstructures》2007,42(1-6):290
Zinc oxide crystals were grown by Chemical Vapor Transport using Contactless Crystal Growth technique. After X-ray examination the 8 off-axis oriented slices were polished using alumina powder followed by a mixture of oxides. The mechanical polishing was followed by chemo-mechanical polishing using colloidal silica in water and supplemented by thermal annealing in an air atmosphere. The range of temperature was between 770 and 1070 C, time of annealing ranged up to 160 h. The quality of surfaces was studied using atomic force microscopy. A wide spectrum of surface morphology was observed. The morphology was dependent on the annealing conditions and additionally on the quality of chemo-mechanical polishing and crystallographic orientation of the surfaces. It was found possible to obtain the lowest RMS surface roughness factor in extremely different annealing conditions. The best annealing procedure for surface improvement was investigated. 相似文献
18.
A. Al-Hajry Ahmad Umar M. Vaseem M.S. Al-Assiri F. El-Tantawy M. Bououdina S. Al-Heniti Y.-B. Hahn 《Superlattices and Microstructures》2008,44(2):216-222
Flower-shaped β- Ni(OH)2 structures composed of thin nanosheet networks have been synthesized via the simple aqueous solution route by using nickel chloride and ammonium hydroxide at 65 C in 4 h. The general morphological observations revealed that the flowers are composed of thin nanosheets which were connected to each other in such a manner that they form network-like morphologies. Moreover, single-crystalline flower-shaped NiO structures composed of thin nanosheets were also obtained by thermal decomposition of flower-shaped β- Ni(OH)2 structures. The shape of nanosheet networks in β- Ni(OH)2 was sustained after thermal decomposition to NiO however, some broken nanosheets were also observed from the flower-shaped structures of NiO. The as-prepared products were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), high-resolution TEM (HRTEM), Fourier transform infrared spectroscopy (FTIR), and Thermogravimetric analysis (TGA). 相似文献
19.
R.T. Rajendra Kumar J. Grabowska J.P. Mosnier M.O. Henry E. McGlynn 《Superlattices and Microstructures》2007,42(1-6):337
ZnO nanostructures are grown on Au-catalyzed Si substrates by vapour phase transport between 800 and 1150 C. Nanostructures grown at 800 C are mainly rod-like in structure with diameters of <200 nm. Increasing growth temperature yields combination growth modes with 2D structures (nanowalls/nanosheets) connecting 1D nanorods at intermediate temperatures and a 3D growth mode of foam-like appearance at the highest temperatures. The present work indicates that it may be possible to systematically control the morphology of ZnO nanostructures by varying the growth temperature. 相似文献
20.
C. Sartel S. Gautier S. Ould Saad Hamady N. Maloufi J. Martin A. Sirenko A. Ougazzaden 《Superlattices and Microstructures》2006,40(4-6):476
Thin films of GaN with the V/III≈10 ratio were grown by low-pressure metal organic vapour phase epitaxy (LP-MOVPE) using N2 and Dimethylhydrazine (DMHy) as a carrier gas and nitrogen precursor, respectively. For the growth temperatures in the range from 550 to 690 C the GaN layers exhibited good surface morphology. In the temperature range from approximately 550 to 610 C, the growth rate increases with increasing temperature, characteristic of the process limited by surface kinetics with the activation energy of approximately 36 kcal/mol. For the temperatures between 620 and 690 C, the growth rate was nearly independent of temperature, which is indicative of a mass transport limited growth. The activation energy was about 4.6 kcal/mol. Micro Raman spectroscopy revealed a significant relaxation of the selection rules for the scattering by the optical phonons in the films grown at lower temperatures. Variation of the intensity ratio for and E1 phonon modes has been attributed to the changes in the structural quality of the films grown at different temperatures. 相似文献