Single-crystalline CdTe nanowire field effect transisitor as a nanowire- based photodetector

A schematic view of the furnace used for the CdTe nanowire synthesis by the vapor-liquid-solid (VLS) technique is shown in figure S1. In this system, the carrier gas transports the source material vapors from upstream to downstream in the quartz tube. The CdTe powder (Alfa company, 99.99%), 0.03g for all samples, was placed in a high-purity alumina crucible located at the source position of the quartz tube. A silicon wafer substrate was thermally oxidized to obtain a silicon oxide layer (150 nm) and then 1 nm gold layer was deposited on the substrate by electron beam evaporator. The position of the silicon substrate in the growth region was determined by comparing the obtained results for 6 substrates, placed along the entire area of the synthesis region. There is a temperature gradient in the growth region in the quartz tube and therefore we selected the best position where we obtained the highest CdTe growth density. Prior to beginning the heating process, the air in the system was purged by flushing with nitrogen inside the quartz tube. Then the gases inside the tube were removed using a vacuum pump at ~ 10-3 Torr. This process was repeated three times to ensure that oxygen was completely eliminated. Then the system was heated at a rate of 20 oC/min to the set temperatures under constant Ar and H2 flow rates of 10 and 5 standard cubic centimeter per minute (sccm). The system was cooled down to room temperature under vacuum conditions after a 60 minute synthesis period when a dark gray coating on the substrate was observed.