Quasi-one Dimensional Cu₂S Nanostructure: Fabrication And Optoelectronic Characteristics

Cuprous sulfide (Cu2S, Eg=1.26 eV) is a kind of important Ⅱ-Ⅵ group semiconductor material which has important applications in fields such as photodetector, photovoltaic, memory and biological sensor devices. With the development of nanotechnology, controllable synthesis of Cu2S nanostructures has attracted great attention. Till now, significant progresses have been made in the controllable synthesis of quasi one-dimensional nanostructures with high purity and high crystallinity through the chemical vapor deposition (CVD) method. However, the controllable synthesis of Cu2S nanostructures has rarely been reported. Herein, we researched the controllable synthesis of Cu2S quasi one-dimensional nanostructures with high purity and high crystallinity through the CVD method. The optical and electrical properties as well as the application in the field of nanodevices were systematically researched. The main research results are as follows:1. Face-centered cubic Cu2S nanowires with length of up to 50 μm and diameters in the range of 100-500 nm were controllable synthesized using CuCl and S powder as copper source and S source respectively through the thermal evaporation method using a mixed gas of Ar (10 sccm) and H2 (50 sccm) as the carrier gas under a higher chamber pressure (about 700 Torr). It was found that the higher concentration of H2 and reaction pressure will promote the growth of quasi one-dimensional nanostructures. The trace copper microcrystalline formed at the early stage by reducing was suggested to be the catalyst, which promoted the growth of the quasi one-dimensional nanostructures according to the VLS growth mechanism.2. To assess the electrical properties of the Cu2S NWs, bottom-gate field-effect transistors (FETs) based on an individual Cu2S NW were constructed which using the n+-Si/SiO2 (300 nm) as the substrate. Electrical characterization showed that the source-drain current decreases with the increase of the gate voltage which confirms the typical p-type conduction. The as-synthesized Cu2S nanowires have a conductivity of about 595 S cm-1 and a hole mobility (μh) of about 71.92 cm2 V-1 s-1.3. For the electrical characterization of the p-Cu2S/n-Si heterojunction, the Au (30 nm) electrodes were deposited onto the as-grown dense Cu2S nanostructures layer on the n-Si substrate with a shadow mask. Further study reveals that Cu2S/Si p-n heterojunction exhibits distinct rectifying characteristics with a turn-on voltage of ～0.6 V and a rectification ratio of ～300 at ±1 V in the dark and a pronounced photovoltaic behavior with an open circuit voltage (Voc) of 0.09 V and a short circuit current (Isc) of 65 nA when illuminated by the NIR light (790 run,0.35 mW cm-2), giving rise to a responsivity (R) about 0.75 mA W-1 and specific detectivity (D*) 6.65×1010 cm Hz1/2 W-1 at zero bias, which suggests the potential of as-synthesized Cu2S nanowires applied in the field of self-driven NIR photodetector.