共查询到20条相似文献,搜索用时 31 毫秒
1.
Mina NeghabiAbbas Behjat 《Current Applied Physics》2012,12(2):597-601
Organic light emitting diodes (OLEDs) of ITO/PEDOT:PSS/TPD:Alq3:C60/Al with different C60 concentrations (0-6.0 wt.%) have been fabricated. The physical parameters including electrical and optical properties of the samples have been measured by Luminance-current-voltage (L-I-V) characteristics and optical absorbance. The current-voltage characteristics indicate that field-emission tunneling injection dominates in the diodes at high applied voltages. It is found that with increasing the concentration of C60, the injection barrier for holes slightly reduces and the hole’s mobility increases over two orders of magnitude. Also, electroluminescence enhances with the presence of C60 in the blend; optimum current efficiency occurs at 3 wt% C60. The method provides a simple way of increasing the efficiency of OLEDs. 相似文献
2.
Tomoaki Sawabe Koshi Okamura Tomoki Sueyoshi Takashi Miyamoto Kazuhiro Kudo Nobuo Ueno Masakazu Nakamura 《Applied Physics A: Materials Science & Processing》2009,95(1):225-232
Vertical electrical conduction in Au/(polycrystal-line pentacene)/Al diode structures and the influence of the kinetic energy
of incident Au atoms on the conduction property have been comprehensively studied using current–voltage–temperature (I–V–T) measurements, ultraviolet photoelectron spectroscopy (UPS), atomic-force-microscope (AFM) current imaging, etc. In the I–V characteristics, a symmetrical ohmic current component appeared when a low voltage was applied, and a super-linear one appeared
when a high positive voltage was applied to Au. The component in the high-forward-voltage region was concluded to be a thermionic
emission of holes from Au with a 0.23-eV injection barrier, which is the normal hole conduction through the highest occupied
molecular orbital of pentacene. On the other hand, the ohmic component was concluded to be a metal-like electron transport
through high-density gap states at grain boundaries which were induced by the Au penetration into pentacene. UPS and I–V–T measurements clearly indicated the generation of the gap states and the enhancement of their density by the reduction of
Au kinetic energy. For vertical-type devices with polycrystalline organic films, the ohmic conduction through the grain boundary
will increase the leakage current. On the contrary, it possibly enhances the carrier injection in lateral-type transistors
in the case of top-contact configuration. 相似文献
3.
The relationship between the diffusivity D
n
and the mobility μ
n
of chemically doped organic n-type semiconductors exhibiting a disordered band structure is presented. These semiconductors
have a Gaussian-type density of states. So, calculations have been performed to elucidate the dependence of D
n
/μ
n
on the various parameters of this Gaussian density of states. Y. Roichman and N. Tessler (Appl. Phys. Lett. 80:1948, 2002), and subsequently Peng et al. (Appl. Phys. A 86:225, 2007), conducted numerical simulations to study this diffusivity–mobility relationship in organic semiconductors. However, almost
all other previous studies of the diffusivity–mobility relationship for inorganic semiconductors are based on Fermi–Dirac
integrals. An analytical formulation has therefore been developed for the diffusivity/mobility relationship for organic semiconductors
based on Fermi–Dirac integrals. The D
n
/μ
n
relationship is general enough to be applicable to both non-degenerate and degenerate organic semiconductors. It may be an
important tool to study electrical transport in these semiconductors. 相似文献
4.
N. I. Alekseev 《Technical Physics》1998,43(5):535-538
The influence of the escape of fast plasma electrons on the electron distribution function (EDF) in a low-voltage cesium Knudsen
arc is discussed. It is shown that even with a large Knudsen parameter l
e
/h∼5–10 (where h is the gap and l
e
is the mean free path of electrons with energy of the order of the anode barrier) the electron flux from the plasma to the
anode is virtually identical to that calculated with a Maxwellian EDF.
Zh. Tekh. Fiz. 68, 61–64 (May 1998) 相似文献
5.
Safi Altunöz Hüseyin Çelik Mehmet Cankurtaran 《Central European Journal of Physics》2008,6(3):479-490
The mobility of electrons in vertical transport in GaAs/Ga1−y
Al
y
As barrier structures was investigated using geometric magnetoresistance measurements in the dark. The samples studied had
Ga1−y
Al
y
As (0 ≤ y ≤ 0:26) linearly graded barriers between the n+-GaAs contacts and the Ga0:74Al0:26As central barrier, which contain N
w
(=0, 2, 4, 7 and 10) n-doped GaAs quantum wells. The mobility was determined as functions of (i) temperature (80–290 K) at
low applied voltage (0.01–0.1 V) and (ii) applied voltage (0.005–1.6 V) at selected temperatures in the range 3.5–290 K. The
experimental results for the temperature dependence of low-field mobility suggest that space-charge scattering is dominant
in the samples with N
w
=0 and 2, whereas ionized impurity scattering is dominant in the samples with N
w
=4, 7 and 10. The effect of polar optical phonon scattering on the mobility becomes significant in all barrier structures
at temperatures above about 200 K. The difference between the measured mobility and the calculated total mobility in the samples
with N
w
=4, 7 and 10, observed above 200 K, is attributed to the reflection of electrons from well-barrier interfaces in the quantum
wells and interface roughness scattering. The rapid decrease of mobility with applied voltage at high voltages is explained
by intervalley scattering of hot electrons.
相似文献
6.
We have theoretically investigated the thermal characteristics of double-channel ridge–waveguide InGaAs/InAlAs/InP quantum
cascade lasers (QCLs) using a two-dimensional heat dissipation model. The temperature distribution, heat flow, and thermal
conductance (G
th) of QCLs were obtained through the thermal simulation. A thick electroplated Au around the laser ridges helps to improve
the heat dissipation from devices, being good enough to substitute the buried heterostructure (BH) by InP regrowth for epilayer-up
bonded lasers. The effects of the device geometry (i.e., ridge width and cavity length) on the G
th of QCLs were investigated. With 5 μm thick electroplated Au, the G
th is increased with the decrease of ridge width, indicating an improvement from G
th=177 W/K⋅cm2 at W=40 μm to G
th=301 W/K⋅cm2 at W=9 μm for 2 mm long lasers. For the 9 μm×2 mm epilayer-down bonded laser with 5 μm thick electroplated Au, the use of InP
contact layer leads to a further improvement of 13% in G
th, and it was totally raised by 45% corresponding to 436 W/K⋅cm2 compared to the epilayer-up bonded laser with InGaAs contact layer. It is found that the epilayer-down bonded 9 μm wide BH
laser with InP contact layer leads to the highest G
th=449 W/K⋅cm2. The theoretical results were also compared with available obtained experimentally data. 相似文献
7.
P. Kammel V. A. Andreev D. V. Balin R. M. Carey T. Case D. B. Chitwood S. M. Clayton K. M. Crowe J. Deutsch P. T. Debevec P. U. Dick A. Dijksman J. Egger D. Fahrni A. A. Fetisov S. J. Freedman V. A. Ganzha B. Gartner J. Govaerts F. E. Gray F. J. Hartmann W. D. Herold D. W. Hertzog V. I. Jatsoura A. G. Krivshich B. Lauss E. M. Maev O. E. Maev V. E. Markushin C. J. G. Onderwater C. Petitjean G. E. Petrov C. C. Polly R. Prieels S. M. Sadetsky G. N. Schapkin R. Schmidt G. G. Semenchuk M. Soroka A. A. Vorobyov N. I. Voropaev 《Hyperfine Interactions》2001,138(1-4):435-443
The aim of the μCap experiment is a 1% measurement of the singlet capture rate Λ
S
for the basic electro-weak reaction μ + p → n + νμ. This observable is sensitive to the weak form-factors of the nucleon, in particular to the induced pseudoscalar coupling
constant g
P
. It will provide a rigorous test of theoretical predictions based on the Standard Model and effective theories of QCD. The
present method is based on high precision lifetime measurements of μ− in hydrogen gas and the comparison with the free μ+ lifetime. The μ− experiment will be performed in ultra-clean, deuterium-depleted H2 gas at 10 bar. Low density compared to liquid H2 is chosen to avoid uncertainties due to ppμ formation. A time projection chamber acts as a pure hydrogen active target. It defines the muon stop position in 3D and
detects rare background reactions. Decay electrons are tracked in cylindrical wire-chambers and a scintillator array covering
75% of 4π.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
Zhaokui Wang Shigeki Naka Hiroyuki Okada 《Applied Physics A: Materials Science & Processing》2011,102(3):681-687
Injection properties of electrons and holes in a mixed single layer organic light emitting device with mixed small molecules
tris-(8-hydroxy-quinoline) aluminum (Alq3), 2,5-bis(6′-(2′,2″-bipyridyl))-1,1-dimethyl-3,4-diphenylsilole (PyPySPyPy), 4′-bis[N-(1-napthyl)-N-phenyl-amino]biphenyl
(α-NPD), and 5,6,11,12-tetraphenylnaphthacene (rubrene) were investigated using Au/MoO3 as hole and Al alloy as electron injection electrodes. On the basis of measuring the temperature dependence of currents through
the interface between the electrodes and the mixed single organic layer, the carrier injection mechanism was primarily ascribed
to the Schottky thermionic emission with the barrier height of 0.25 eV for holes and 0.67 eV for electrons. By adding the
dopant material rubrene and the electron transport material PyPySPyPy into the mixed single layer, the barrier height of electrons
could be reduced. The interfacial state analysis demonstrated that the electron barrier height was also dependent on the interfacial
conditions of the device. 相似文献
9.
10.
M. C. Gather R. Jin J. de Mello D. D. C. Bradley K. Meerholz 《Applied physics. B, Lasers and optics》2009,95(1):113-124
We report on electromodulation (EM) spectroscopy studies of phosphorescent multi-layer organic light-emitting diodes (OLEDs)
that are processed from solution. Compared to conventional single-layer OLEDs, they comprise an additional layer of a crosslinkable,
oxetane-functionalized triphenylamine-dimer (XTPD) that is inserted between the PEDOT:PSS anode and the emissive layer. Devices
with optimized stack architecture feature reduced operating voltages and reach a current efficiency approaching 40 cd/A—twice
as much as the corresponding single-layer device. Using EM measurements, we quantify the electric field in the XTPD layer
and the emissive layer of such a multi-layer OLED and also measure the average electric field in a single-layer reference
device. By comparing the dependence of the internal field on the applied voltage for devices with and without the XTPD layer,
we find that in the device containing the XTPD layer there is an increased accumulation of electrons at the anode side of
the emissive layer. This accumulation enhances the recombination probability and supports the injection of holes into the
emissive layer which explains the observed efficiency improvement and reduction in operating voltage compared to conventional
single-layer OLEDs. 相似文献
11.
有机发光器件的宏观特性与有机层中的电场和载流子浓度分布密切相关。建立的有机电致发光器件模型是由两个金属电极中间夹一层有机发光薄膜材料组成的单层器件,金属与有机发光层之间为欧姆接触。模型以载流子运动的扩散-漂移理论为基础,利用数值方法研究了有机发光层中双极载流子注入时的电势、电场、载流子浓度和复合密度分布。分析结果表明:当两种载流子的迁移率相同时,电场强度、载流子浓度、复合密度的分布呈对称形式。而当电子和空穴的迁移率μn和μp相差比较大时,高迁移率的载流子不仅仅分布在注入端附近而且还有一小部分能够传输到另一端,而低迁移率的载流子只分布在其注入端附近;当μn、μp的大小相差不大时,载流子传输情况就介于两者之间。当μn/μp的比值变化时,电场强度的极大值向载流子迁移率小的注入端偏移。 相似文献
12.
G. Chaidogiannos F. Petraki N. Glezos S. Kennou S. Ne?p?rek 《Applied Physics A: Materials Science & Processing》2009,96(3):763-767
The class of sodium salts of sulphonated metal phthalocyanines (MePCS
x
, S = SO3Na, x=1–4) was investigated as a p-type channel component in organic field-effect transistors (OFETs). The solubility of these
materials appears to be enhanced compared to their non-sulphonated counterparts (MePCs). We fabricated transistors based on
MePCS
x
varying the central metal atom (Me = Ni, Co, Zn, Al) and we evaluated the dependence of transistor performance on the nature
of the central atom and the degree of sulphonation. The best results were obtained in the case of Ni and low sulphur content.
In this case the mobility value is μ=1.08 cm2 V−1 s−1 and the on/off current ratio ∼103. The degree of sulphonation affects the electric field inside the active film in a way analogous to the case of polyelectrolyte-gated
OFETs. The Na+ counter ions present in the channel contribute to the device characteristics but their concentration should be controlled
in order to optimize device performance. 相似文献
13.
M. Weber P. Birrer F. N. Gygax B. Hitti E. Lippelt H. Maletta A. Schenck 《Hyperfine Interactions》1991,63(1-4):207-212
Possibleμ
+ sites have been identified by a comparison of measured spontaneous internal fields in YBa2Cu3O6+δ and REBa2Cu3O7−δ and of measured second moments and width of transverse field powder spectra with the corresponding calculated quantities.
In the YBa2Cu3O7 system only one possibleμ
+ site emerges at a distance of ∼1.05 A from a chain oxygen O(4) at the position (0.15(1), 0.44(1), 0.071(1)). In the system
YBa2Cu3O6 the only possibleμ
+ sites are near to an oxygen O(1) with z/c=0.133 and the same distance as above. The analysis leads also to improved valuesμ
Ho = 2.2(1)μ
B andμ
Cu = 0.67(4)μ
B and to a determination of the latters direction:μ
Cu ‖〈110〉. 相似文献
14.
Summary Experiments show that the Hall resistivityρ
xy
of InSe bulk crystals is quantized into integer multiples ofh/e
2. Quantum Hall effect in InSe is explained as a result of plane defects in InSe crystals. The electrons in bulk InSe are localized
at these defects at low temperatures forming regions with two-dimensional conductivity. Concentration of electrons in these
regions isN
2D=2·1011 cm−2 and their mobility μ=2·104cm2/V·s.
To speed up publication, the authors of this paper have agreed to not receive the proofs for correction. 相似文献
15.
D.C. Eder G. Pretzler E. Fill K. Eidmann A. Saemann 《Applied physics. B, Lasers and optics》2000,70(2):211-217
The spatial dependence of K
α emission generated from laser-produced hot electrons is investigated experimentally and theoretically. In addition, the conversion
efficiency of K
α production as a function of laser intensity is measured and compared with modeling results. We use the terawatt Ti:sapphire
laser at MPQ and vary the peak intensity from 1015 to 1018 W/cm2 with a pulse duration of 200 fs. A solid Cu target is placed at various positions in the laser focus, which allows one to
vary the intensity but keep the total energy on the target constant. When the target is near best focus, the FWHM of the K
α emission, measured using a knife-edge, is considerably larger than the FWHM of the laser intensity. In measuring the efficiency
of K
α production using the fundamental wavelength of the laser, a clear maximum of K
α emission is observed at a position away from best focus, where the peak intensity is down by more than an order of magnitude
from the value at best focus. When the second harmonic of the laser is used, the K
α emission is peaked near best focus. The K
α emission from layer targets is used to obtain an estimate of the temperature of the hot electrons. Modeling of K
α production, using a Monte Carlo electron/photon transport code, shows the relationship between incident electron energy and
the emitted K
α emission. Efficient K
α generation from the low-intensity wings of the laser pulse contributes to the large spot size of the K
α emission. The lower electron temperatures that are expected for the second harmonic explain the differences in the location
of maximum K
α emission for the two wavelengths. We discuss the use of K
α emission in photoionizing inner-shell electrons with the goal of achieving X-ray lasing at short wavelengths.
Received: 6 April 1999 / Revised version: 31 May 1999 / Published online: 11 August 1999 相似文献
16.
A. Adamczak M. P. Faifman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,51(3):341-345
The kinetics of muon-catalyzed-fusion processes (μCF) in pure D2 gas have been studied by means of Monte Carlo simulations for various target temperatures and densities. In particular, the
role of resonant and non-resonant ddμ formation in μCF has been investigated. It has been shown that non-resonant formation can be directly observed at very short times in the
neutron time spectra from μCF for low-density D2 targets. The time spectra of neutrons from the low-temperature ortho-D2 and para-D2 gas targets have been calculated. These spectra display a strong ortho-para effect, which agrees with experimental results
for the dilute-gas D2 targets. 相似文献
17.
Zongqing Ma Yongchang Liu Zhizhong Dong Liming Yu Zhiming Gao Qian Zhao 《Applied Physics A: Materials Science & Processing》2009,96(4):975-978
Based on the phase identification and microstructural observation, it is found that the Cu addition in the μm-SiC-doped samples
could depress the reaction between Mg and SiC and thus decrease the amount of both C substitution for B and the Mg2Si nanoparticles. As a result, compared to the only μm-SiC-doped MgB2 sample, the T
c
of the Cu and μm-SiC multi-doped MgB2 sample is improved and the J
c
in high fields is deteriorated. 相似文献
18.
Summary Hall mobility, μH, and electrical conductivity, σ, of unhydrogenated amorphous-gallium-arsenide films, prepared by r.f. sputtering, have been
measured. Conductivity as a function of temperature shows a variable-range hopping mechanism atT<260 K, while at high temperature, conductivity and Hall mobility are both thermally activated. The results are interpreted
in terms of the presence of defect complexes due to an excess of Ga. The stoichiometry and the structure of the films are
used to explain the behaviour and the values of μH. The values of the activation energy of the conductivity seem in agreement with theoretical calculations on the position
of electronic states created by defect complexes in the mobility-gap of a-GaAs. 相似文献
19.
S. A. Ahmed 《Applied Physics A: Materials Science & Processing》2008,92(3):565-570
Thermoelectric power and electrical resistivity measurements on polycrystalline samples of Bi2Se3 and stoichiometric ternary compound in the quasi-binary system SnSe–Bi2Se3 in the temperature range of 90–420 K are presented and explained assuming the existence of an impurity band. The variation
of the electron concentration with temperature above 300 K is explained in terms of the thermal activation of a shallow donor,
by using a single conduction band model. The density of states effective mass m
*=0.15m
0 of the electrons, the activation energy of the donors, their concentration, and the compensation ratio are estimated. The
temperature dependence of the electron mobility in conduction band is analyzed by taking into account the scattering of the
charge carriers by acoustic phonon, optical phonon, and polar optical phonon as well as by alloy and ionized impurity modes.
On the other hand, by considering the two-band model with electrons in both the conduction and impurity bands, the change
in the electrical resistivity with temperature between 420 and 90 K is explained. 相似文献
20.
Nicolás Fernández-García Oscar Rosas-Ortiz 《International Journal of Theoretical Physics》2011,50(7):2057-2066
Semiclassical approximations are implemented in the calculation of position and width of low-energy resonances for radial
barriers. The numerical integrations are delimited by τ/τ
life≪8, with τ the period of a classical particle in the barrier trap and τ
life the resonance lifetime. These energies are used in the construction of ‘haired’ short-range potentials as the supersymmetric
partners of a given radial barrier. The new potentials could be useful in the study of the transient phenomena which give
rise to the Moshinsky’s diffraction in time. 相似文献