The Synthesis Of N-type ZnS Nanoribbons And Its Application In Schottky Devices

The Ⅱ-Ⅵ group semiconductor zinc selenide (ZnS), with a direct band-gap of 3.70eV at room temperature, is regarded as one of the most promising materials for optoelectronic applications and the studies on the quasi-one dimensional ZnS nanostructures have caused great attention. Current research on ZnS nanostructures is mainly focused on the material growth, microstructure control, characterizations and its optical properties. Studies on their transport properties and device applications are rarely due to the presence of carrier trapping states at the nanostructures surface because of the large surface-to-volume ratio resulting in the difficulty of obtaining ohmic contact. Study of related devices was limited in simple device configuration such as field effect transistor, While the study of other important device configuration (Schottky barrier diode for example) has not been involved.Herein, n-type ZnS nanoribbons (NRs) have been synthesized by using zinc chloride (ZnCl2) as the n-type dopant via a thermal evaporation method. Cl was selected as the n-type dopant since it has been reported to be an efficient dopant for achieving high levels of n-type doping with fewer defects in n-ZnS film. Field-effect transistors (FETs) were constructed with single ZnS:Cl NR, which verified the n-type nature of ZnS:Cl NR with an electron mobility of 64.9cm2V-2s-1 and electron concentration of 5.7×1017cm-3. Electrodes with good ohmic contact were defined by copper mask and pulsed laser deposition (PLD) system with KrFexcimer laser. The copper mask was made by lithography, followed etch on the copper foils. By using this method, accurate contact shape can be obtained, and the pollution on the NRs by photoresist can be avoided. In addition, Schottky barrier diodes (SBDs) based on the ZnS:Cl NRs/Au junctions were fabricated. The SBDs exhibited typical rectifying behavior (rectification ratio>103) with Schottky barrier height of 0.64 eV and a small ideality factor of ～1.05 at 320 K. Interestingly, n-ZnS:Cl NR/Au nano-SBD device exhibited pronounced negative photoresponse at forward bias, but positive photoresponse at reverse bias under 365 nm UV light irradiation and the detailed reason for this phenomenon was explained by the energy band diagram. The SBD photodetector device showed an excellent performance comparing with similar semiconductor devices. Its respectivity and gain were 9.1 AW-1 and 33, respectively. At the same time the Ilight/Idark ratio (365nm UV) could reach 180.