UV response of ZnO nanowire nanosensor has been studied under ambient condition. By utilizing Schottky contact instead of Ohmic contact in device fabrication, the UV sensitivity of the nanosensor has been improved by four orders of magnitude, and the reset time has been drastically reduced from ϳ417 to ϳ0.8 s. By further surface functionalization with function polymers, the reset time has been reduced to ϳ20 ms even without correcting the electronic response of the measurement system. These results demonstrate an effective approach for building high response and fast reset UV detectors. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3133358͔ Ultraviolet ͑UV͒ photon detectors have a wide range of applications from environmental monitoring, missile launching detection, space research, high temperature flame detection to optical communications.1 For these applications, fast response time, fast reset time, high selectivity, high responsivity, and good signal-to-noise ratio are commonly desired characteristics.2 For UV photon detector based on polycrystalline ZnO thin film, a slow response time ranging from a few minutes to several hours is commonly observed.3,4 Due to large surface-to-volume ratio and reduced dimensionality of the active area, ZnO nanostructures are expected to have high photon conductance.5 Kind et al. 6 reported the photon response of a single ZnO nanowire ͑NW͒ under UV illumination, which has also been studied by other groups.7-9 Most of the studies have been focused on the mechanism investigation 10,11 and improving the sensitivity. 9,12 For example, Lao et al. 9 have improved the sensitivity of the ZnO NW UV nanosensor ͑NS͒ for five orders of magnitude by functionalizing the surface of ZnO nanobelts using polymers that have a high absorption at the UV range. However, little attention has been paid on improving the response and recovery time 13 especially the reset time ͑defined as the time need to recovery to 1 / e ͑37%͒ of the maximum photocurrent͒.In this letter, we demonstrate effective ways for improving both the sensitivity and reset time of ZnO NW NSs. By fabricating Schottky type ͑ST͒ devices instead of Ohmic type ͑OT͒ devices, the UV sensitivity of ZnO NW NS has been improved for four orders of magnitude, and the reset time has been decreased from ϳ417 to ϳ0.8 s. By further surface coating with positive charged poly͑diallydimethylammonium chloride͒ ͑PDADMAC͒ and negative charged poly͑sodium 4-styrenesulfonate͒ ͑PSS͒, the reset time has been decreased to ϳ20 ms even without correcting the electronic response of the measurement system. The ZnO NWs for the NS fabrication were synthesized by thermal evaporation of ZnO powders without using any catalyst.14 UV response of our devices was characterized by a portable UV lamp ͑Spectroline, Model ENF-280C, 365 nm͒. The photon-response spectrum measurement was carried out in a PTI QuantaMaster Luminescence ͑QM 3PH͒ system. All of the measurements were carried out at room temperature in ambient condition.We first studied the performance of...

A Schottky barrier can be formed at the interface between a metal electrode and a semiconductor. The current passing through the metal-semiconductor contact is mainly controlled by the barrier height and barrier width. In conventional nanodevices, Schottky contacts are usually avoided in order to enhance the contribution made by the nanowires or nanotubes to the detected signal. We present a key idea of using the Schottky contact to achieve supersensitive and fast response nanowire-based nanosensors. We have illustrated this idea on several platforms: UV sensors, biosensors, and gas sensors. The gigantic enhancement in sensitivity of up to 5 orders of magnitude shows that an effective usage of the Schottky contact can be very beneficial to the sensitivity of nanosensors.

We present high efficiency and stable inverted PSCs (i-PSC) by employing sol-gel processed simultaneously doped ZnO by Indium and fullerene derivative (BisNPC60-OH) (denoted as InZnO-BisC60) film as cathode interlayer and PTB7-Th:PC71BM as the active layer (where PTB7-Th is a low bandgap polymer we proposed previously). This dual-doped ZnO, InZnO-BisC60, film shows dual and opposite gradient dopant concentration profiles, being rich in fullerene derivative at the cathode surface in contact with active layer and rich in In at the cathode surface in contact with the ITO surface. Such doping in ZnO not only gives improved surface conductivity by a factor of 270 (from 0.015 to 4.06 S cm−1) but also provides enhanced electron mobility by a factor of 132 (from 8.25*10−5 to 1.09*10−2 cm2 V−1 s−1). The resulting i-PSC exhibits the improved PCE 10.31% relative to that with ZnO without doping 8.25%. This PCE 10.31% is the best result among the reported values so far for single junction PSC.

A new single nanowire based nanosensor is demonstrated for illustrating its ultrahigh sensitivity for gas sensing. The device is composed of a single ZnO nanowire mounted on Pt electrodes with one end in Ohmic contact and the other end in Schottky contact. The Schottky contact functions as a "gate" that controls the current flowing through the entire system. By tuning the Schottky barrier height through the responsive variation of the surface chemisorbed gases and the amplification role played by the nanowire to Schottky barrier effect, an ultrahigh sensitivity of 32,000% was achieved using the Schottky contacted device operated in reverse bias mode at 275 degrees C for detection of 400 ppm CO, which is 4 orders of magnitude higher than that obtained using an Ohmic contact device under the same conditions. In addition, the response time and reset time have been shortened by a factor of 7. The methodology and principle illustrated in the paper present a new sensing mechanism that can be readily and extensively applied to other gas sensing systems.