We report a flexible carbon nanotube ͑CNT͒ thin-film transistor ͑TFT͒ fabricated solely by ink-jet printing technology. The TFT is top gate configured, consisting of source and drain electrodes, a carrier transport layer based on an ultrapure, high-density ͑Ͼ1000 CNTs/ m 2 ͒ CNT thin film, an ion-gel gate dielectric layer, and a poly͑3,4-ethylenedioxythiophene͒ top gate electrode. All the TFT elements are ink-jet printed at room temperature on a polyimide substrate without involving any photolithography patterning or surface pretreatment steps. This CNT-TFT exhibits a high operating frequency of over 5 GHz and an on-off ratio of over 100. Such an all-ink-jet-printed process eliminates the need for lithography, vacuum processing, and metallization procedures and thus provides a promising technology for low-cost, high-throughput fabrication of large-area high-speed flexible electronic circuits on virtually any desired flexible substrate.Printing thin-film transistors ͑TFTs͒ on flexible substrates at room temperature offers a cost-effective way to achieve mass production of large-area electronic circuits without using special lithography equipment. It is expected to provide an enabling technology for many emerging applications such as flexible displays, radio frequency identification ͑RFID͒ tags, electronic papers, and smart skins, just to name a few. Printed flexible electronics have been reported by using various organic semiconducting polymers. 1-3 However, the carrier mobility of organic semiconducting polymers is still less than 1.5 cm 2 / V s, 1-3 which limits the device operation speed to only a few kilohertz. Carbon nanotube ͑CNT͒, a material with exceptional aspect ratio and great mechanical flexibility, has shown great promises as an active carrier transport material in making high-speed flexible field-effect transistors ͑FETs͒. 4-12 Extraordinary field-effect mobility as high as 79 000 cm 2 / V s was reported in the FETs based on individual CNTs. 5 Due to the ultrahigh field-effect mobility, CNT-based flexible FETs are capable of achieving high-speed ͑gigahertz͒ operation. [13][14][15] However, most of the reported FETs were based on CNTs grown using chemical vapor deposition ͑CVD͒, 16,17 which generally requires an extremely high temperature, typically Ͼ900°C. 5,16,17 This represents a major obstacle to fabricating electronic devices on flexible substrates because most flexible substrates are unable to survive such a high CVD growth temperature. FETs based on solution-processable CNT thin films 6-12 can be fabricated at room temperature and are thus especially suitable for printed electronics on flexible substrates. However, the sidewalls of as-produced nanotubes are covered by amorphous carbon ͑␣-C͒, which is a very common carbonaceous impurity. 18 Such impurities would tremendously restrict the transport of carriers in the formed CNT thin films and seriously limit the field-effect mobility of the CNT-TFTs. 18,19 High field-effect mobility CNT-TFTs can be achieved by using ultrapure electronics-grade CN...

In this letter, we report a quantum dot photodetector enhanced by Fano-type interference in a metallic two-dimensional (2D) subwavelength hole array (2DSHA). The photocurrent enhancement wavelength shows an offset from the plasmonic resonant peak and corresponds to a dip in the transmission spectrum of the 2DSHA structure. The offset is attributed to the Fano-type interference in the 2DSHA structure. The asymmetric line shapes of the plasmonic resonance are analyzed and agree well with the two-peak Fano-type interference model. Over 100% enhancement in photodetectivity and photoresponsivity is achieved at the wavelength of the Fano dip of the first order plasmonic mode.

In this letter, a longwave infrared (LWIR) InAs–InGaAs quantum dot infrared photodetector with a peak detection wavelength of 9.9μm is reported. A large photoresponsivity of 2.5A∕W and a high peak specific photodetectivity D* of 1.1×108cmHz1∕2∕W were obtained at the operating temperature of 190K. The QDIP showed a strong temperature-dependent photoresponsivity over the temperature range from 78to190K. This effect is shown to be attributable to temperature-dependent electron capture probability.

In this paper, we report a quantum dot infrared photodetector (QDIP) enhanced by a backside-configured surface plasmonic structure with an over 40 times peak photocurrent enhancement. The QDIP enhancement by the backside-configured plasmonic structure is compared with that by the top-configured plasmonic structure. The backside-configured plasmonic structure shows much higher photocurrent and photodetectivity D * enhancement.We analyze the excitation of the surface plasmonic waves by the backside-configured and top-configured plasmonic structures. The higher enhancement is attributed to the more efficient surface plasmonic excitation by the backside-configured plasmonic structure.

A voltage-tunable, dual-band, InAs quantum-dot infrared photodetector (QDIP) is reported. The QDIP consists of InAs quantum dot layers with GaAs and In 0.20 Ga 0.80 As capping layers for extended middle infrared (EMIR, 6-8 µm) and long-wave infrared (LWIR, 8-12 µm) detection, respectively. Voltage-tunable single-and dual-band operations were obtained with good photoresponsivity and photodetectivity selectivity. Since the detection band of the QD FPA can be individually tuned by engineering the capping layers of the InAs QDs, this design approach offers great flexibility in detection for a given spectral region.

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In this paper, we analyze near-field vector components of a metallic circular disk array (MCDA) plasmonic optical antenna and their contribution to quantum dot infrared photodetector (QDIP) enhancement. The near-field vector components of the MCDA optical antenna and their distribution in the QD active region are simulated. The near-field overlap integral with the QD active region is calculated at different wavelengths and compared with the QDIP enhancement spectrum. The x-component (E(x)) of the near-field vector shows a larger intensity overlap integral and stronger correlation with the QDIP enhancement than E(z) and thus is determined to be the major near-field component to the QDIP enhancement.

In this paper, we measured the transmission of the 2DSHA surface plasmonic structures and its variation with the hole diameters a of the 2DSHA structures. The relationship between the transmission and the hole diameters a is found to be different from the prediction of Bethe's diffraction theorem. We also found that the photocurrent of the quantum dot (QD) infrared photodetectors (QDIPs) with different QD active layer thicknesses show different dependence on the hole diameters a of the 2DSHA structures. The photocurrent of the QDIPs with 10 active QD layers (10-QDIPs) saturates and starts to decrease as the hole diameter a is larger than 1.6 µm, whereas that of the QDIPs with 20 active QD layers (20-QDIPs) increases linearly with the hole diameter. The difference in the hole-diameter dependence of the 10-QDIPs and the 20-QDIPs is attributed to the variation of the near-field spreading in the vertical (surface-normal) direction due to the change in the hole diameters. An over 6 time (6×) photocurrent enhancement is obtained by optimizing the hole diameter of the 2DSHA surface plasmonic structure.