In this study, we prepared flexible and transparent hybrid electrodes based on an aqueous solution of non-oxidized graphene and single-walled carbon nanotubes. We used a simple halogen intercalation method to obtain high-quality graphene flakes without a redox process and prepared hybrid films using aqueous solutions of graphene, single-walled carbon nanotubes, and sodium dodecyl sulfate surfactant. The hybrid films showed excellent electrode properties, such as an optical transmittance of ≥90%, a sheet resistance of ~3.5 kΩ/sq., a flexibility of up to ε = 3.6% ((R) = 1.4 mm), and a high mechanical stability, even after 103 bending cycles at ε = 2.0% ((R) = 2.5 mm). Using the hybrid electrodes, thin-film transistors (TFTs) were fabricated, which exhibited an electron mobility of ~6.7 cm2 V−1 s−1, a current on-off ratio of ~1.04 × 107, and a subthreshold voltage of ~0.122 V/decade. These electrical properties are comparable with those of TFTs fabricated using Al electrodes. This suggests the possibility of customizing flexible transparent electrodes within a carbon nanomaterial system.
Due to simple planar device structure that is compatible with FET's and low parasitic capacitance, small area Metal-Semiconductor-Metal Photodiodes(MSM PD's) have been one of the most favored detector choices for high speed Optoelectronic Integrated Circuits (OEIC's).Large area MSM PD's, on the other hand, can be also useful in many network and interconnect applications such as FDDl and computer interconnects where they can provide an attractive alternative to p-i-n type counterparts if comparable bandwidth and dark current conditions are met. In case of InCaAs MSM PD's, however, the Schottky barrier height is too low (0.2 eV) to get low dark current when the contacts are formed directly on the material. A recent work has shown that this leakage current may be limited to an acceptable value by growing a thin high-quality InAlAs cap layer of a semiconductor on top of the InGaAs before depositing the Schottky electrode metal, thereby raising the effective barrier C11. The significant charge accumulation problem that results from a large band discontinuity at the InAIAsAnCaAs interface can be solved by inserting a composition graded layer C21.As shown in Fig. 1, the layer structure consists of a 300 nm-thick InAlAs buffer layer, a 27 nm-thick composition graded InAlAsAnCaAs short period superlattice(SPSL) layer, a 1 .O Ct m-thick InCaAs photoabsorption layer, a 27 nm-thick InAIAs/lnCaAs SPSL, and a 30 nm-thick InAlAs Schottky barrier enhancement layer. The epitaxial layers are grown lattice-matched on a semi-insulating InP substrate using MBE. The interdigited metal contacts are made by therm$ evaporation of Cr/Au (200A/1000A). The active area of the photodiodes is 300x300 Ct m , and the finger spacings are 2, 4, and 6 wn. Finger width is made equal to the spacing. No antireflection coating is used. Fig. 2. shows the measured dark current and photocurrent characteristics from an MSM PD with 4 um finger spacing. The calculated dark current densities are shown in Fig. 3, where the dark current density is obtained, by division of the dark current by the total anode (=cathode) metal area of 21,600 pm . In the same figure, the best dark current densities obtained prior to this wobk 14) are included for comparison. If we use the total detectiop (active) area of 90,000 pm , all the dark current density values become less than 1 p A h m . This extremely low value is obtained due to the effectiveness of the Schottky barrier enhancement of the InAlAs layer, a high purity InGaAs absorption layer, and clean processing with Cr/Au metal. The photocurrent corresponds to a responsivity of 0.3 A/W under 1.3 Ct m wavelength laser light with 450 PW optical power. Improvement of responsivity can be made with addition of an antireflection coating. We also notice that knee voltages are quite small (0.2 and 0.5 V under dark and illuminated conditions, respectively), that only a small bias voltage is required to operate this device for the full quantum efficiency. Fig. 4. shows the capacitance-voltage characteristics of oub devices. The va...
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