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Fabrication of ambipolar organic field-effect transistors (OFETs) is essential for the achievement of an organic complementary logic circuit. Ambipolar transports in OFETs with heterojunction structures are realized. We select pentacene as a P-type material and N,N'-bis(4-trifluoromethylben-zyl)perylene-3,4,9,10-tetracarboxylic diimide (PTCDI-TFB) as a n-type material in the active layer of the OFETs. The field-effect transistor shows highly air-stable ambipolar characteristics with a field-effect hole mobility of 0.18 cm2/(V.s) and field-effect electron mobility of 0.031 cm2/(V.s). Furthermore the mobility only slightly decreases after being exposed to air and remains stable even for exposure to air for more than 60 days. The high electron affinity of PTCDI-TFB and the octadecyltrichlorosilane (OTS) self-assembly monolayer between the SiO2 gate dielectric and the organic active layer result in the observed air-stable characteristics of OFETs with high mobility. The results demonstrate that using the OTS as a modified gate insulator layer and using high electron affinity semiconductor materials are two effective methods to fabricate OFETs with air-stable characteristics and high mobility.

We synthesize and purify 9, 9'-bianthracene with the purity up to 96.4%. The electronic and crystallographic structures of 9, 9'-bianthracene are studied. The results of a joint experimental investigation based on a combination of x-ray diffraction (XRD) spectra, hydrogen nuclear magnetic (HNMR) spectra, infrared absorption (FT-IR) spectra, and mass spectra (MS) of 9,9'-bianthracene are obtained. The uniform compact film is observed by an atomic-force microscope (AFM). Organic field effect transistors (OFETs) with an active layer based on the synthesized 9, 9'-bianthracene are fabricated for the first time. Its field-effect mobility is as large as 0.067cm2/(V-s) and the on/off ratio is above 5 × 10.4 The result demonstrates that the oligomerization of a small semiconductor molecule is an effective method to develop high-mobility organic semiconductors.

A comprehensive understanding of the organic semiconductor material pentacene is meaningful for organic field-effect transistors (OFETs). Thin films of pentacene are the most mobile molecular films known to date. This paper reported that the pentacene sample was successfully synthesized. The purity of pentacene is up to 95%. The results of a joint experimental investigation based on a combination of infrared absorption spectra, mass spectra (MS), element analysis, x-ray diffraction (XRD) and atom force microscopy (AFM). The authors fabricated OFET with the synthesized pentacene. Its field effect mobility is about 1.23 cm2/(Vs) and on-off ratio is above 106.

Carbon nitride thin films were prepared by electron-beam evaporation assisted with nitrogen ion bombardment and TiN/CNx composite films were by unbalanced dc magnetron sputtering, respectively. It was found that the sputtered films were better than the evaporated films in hardness and adhesion. The experiments of atomic oxygen action, cold welding, friction and wearing were emphasized, and the results proved that the sputtered TiN/CNx composite films were suitable for space application.

We have investigated the morphology and surface electron states of LiBq 4 deposited on ITO and CuPc/ITO, using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The AFM observations indicate that LiBq 4 can form a much more uniform film on CuPc than that on ITO. Furthermore, X-ray photoelectron spectroscopy (XPS) is utilized to further demonstrate the AFM results. From the analysis of XPS, we found that LiBq 4 molecules have poor thermal stability, they are seriously oxidized during depositing; but when a CuPc layer is inserted between LiBq 4 and ITO film, the oxidation and surface contamination of LiBq 4 are significantly reduced. It is then concluded that the introduction of a CuPc buffer layer under the LiBq 4 film can improve the film quality of LiBq 4 .The XPS results also testified the fact that no coordination bonds between N atoms and B atoms are formed in LiBq 4 molecules, which make LiBq 4 to be potential blue organic light-emitting material.

A numerical model for bilayer organic light-emitting diodes (OLEDs) has been developed on the basis of trapped charge limited conduction. The dependences of the current density on the operation voltage, the thickness and trap properties of the hole transport layer (HTL) and emission layer (EML) in bilayer OLEDs of the structure anode/HTL/EML/cathode have been numerically investigated. It has been found that, for given values of reduced trap depth, total trap density and carrier mobility of HTL and EML, there exists an optimum thickness ratio of HTL to the sum of HTL and EML, by which a maximal current density and hence maximal quantum efficiency and luminance, can be achieved. The current density decreases quickly with the mean trap density and decreases nearly exponentially with the mean reduced trap depth.

The mechanism of carrier transport in organic light-emitting devices is numerically studied, on the basis of trapped-charge-limited conduction with an exponential trap distribution. The spatial distributions of the electrical potential, field and carrier density in the organic layer are calculated and analysed. Most carriers are distributed near the two electrodes, only a few of them are distributed over the remaining part of the organic layer. The carriers are accumulated near the electrodes and the remaining region is almost exhausted of carriers. When the characteristic energy of trap distribution is greater than 0.3 eV, it leads to a reduction of current density. In order to improve the device efficiency, organic materials with minor traps and low characteristic energy should be chosen. The diffusion current is the dominant component near the injection electrode, whereas the drift current dominates the remaining region of the organic layer.

Low resistance ohmic contacts have been fabricated and analyzed to Zn-doped p-type Gap using an annealed Pd/Zn/Pd metalization. It has been found that the Pd/Zn/Pd multilayer structure shows good ohmic characteristics after heat treatment. The results show that the alloying temperature and alloying time are the important factors for the quality of the ohmic contact layer. When the surface hole concentration of the p-type Gap is 2 x 10(17) cm(-3), a specific contact resistance of 6 x 10(-5) Omega cm(2) has been obtained at the optimum alloying temperature of 550 degrees C and the optimum alloying time of 3 min. (C) 1997 Elsevier Science Ltd.

Polycrystalline silicon (poly-Si) thin-film is fabricated on Al-coated planar glass substrates at the temperature below 100 °C, using aluminium-induced crystallized (AIC) amorphous silicon (a-Si) deposited by dc-magnetron sputtering under an electric field. The properties of NA poly-Si films (AIC of dc-magnetron sputtered silicon non-annealing) are characterized by Raman spectroscopy and x-ray diffraction (XRD) spectroscopy. A narrow and symmetrical Raman peak at a wave number of about 521 cm−1 is observed for samples, showing that the films are fully crystallized. XRD spectra reveal that the films are preferentially (111) oriented. Furthermore, the XRD spectrum of the sample prepared without electric field does not show any XRD peaks for poly-Si, which only appears at about 38° for Al (111) orientation. It is indicated that the electric field plays an important role in crystallization of poly-Si during the dc-magnetron sputtering. Thus, high quality poly-Si film can be obtained at low temperature and separate post-deposition step of AIC of a-silicon can be avoided.

The weak localization and weak antilocalization effects in the coherent scattering of two dimensional electron gas(2DEG) have been observed in Al0.22Ga0.78N/GaN heterostructures by the magneto-transport measurement. The change of magnetoresistance from positive to negative under a perpendicular low magnetic field indicates that electron spin-orbit scattering caused by crystal field exists in Al0.22Ga0.78N/GaN heterojunction. The relation between the spin-orbit scattering time and the temperature is discussed for 2DEG, the inelastic scattering time measured by experiment shows a strong temperature dependence according to T-1 rule, which indicates that the electron-electron scattering with small energy transfer is the dominant inelastic process.

This paper studies the detailed beating oscillation in Shubnikov-de Hass (SdH) of magnetic two dimensional electron gas consisting of a modulation doped n type Hg0.82Cd0.16Mn0.02Te/Hg0.3Cd0.7Te first type quantum well, by which found that temperature, gate voltage are both bring the variety of magnetic resistance beating node position. By analyzing beating patterns, gate voltage dependent Rashba spin-orbit splitting can be separated from temperature dependent giant Zeeman splitting.

This paper study the detailed magnetoresistance oscillation in Shubnikov-de Hass (SdH) of magnetic two dimensional electron gas consisting of a modulation doped n type Hg0.82Cd0.16Mn0.02Te/Hg0.3Cd0.7Te first type quantum well by changing temperature and the angle of the sample with aspect of applied magnetic field, by which found that the changing of temperature and tilt angle will cause the varying of beating node position, By analyzing beating patterns, the magnetic angle dependent Landau splitting can be separated from magnetic magnitude dependent Zeeman splitting.

We have investigated the surfaces of the samples LiBq4/ITO and LiBq4/CuPc/ITO. The atomic force microscopy (AFM) observations indicate that different surface morphologies are formed on different substrates, and what is more, x-ray photoelectron spectroscopy is also utilized to further demonstrate the AFM results. It is concluded that the introduction of a CuPc buffer layer under the LiBq4 layer can improve the film quality of LiBq4, and the improvement should be attributed to the differences in molecular structure and electron affinity.