As a direct bandgap semiconductor, indium antimonide (InSb) has the narrowest band gap (0.17 eV at 300 K) and the highest bulk electron mobility (77000 cm²V^-1s^-1) among all of III-V semiconductors. Due to the unique physical properties, it has considerable potential for applications in high-speed, low-power electronics and infrared optoelectronics.^[1]-[3] Adding other elements is a possible method to adjust its bandgap, but it is very difficult to achieve doping during the electrodeposition and sol-gel deposition processes. In this study, the bandgap of InSb nanowires (NWs) is tuned by substitute of indium with varying the aluminum concentration. The Al_xIn_1-xSb nanowires were synthesized by using a vacuum hydraulic pressure injection process with anodic aluminum oxide (AAO) template assisted. Unlike vapor deposition processes or chemosynthesis, when a stoichiometric bulk material was produced, the following casting would not change the composite ratio of alloys until the injection process ended. This process has five main steps: first, fabrication of a nanotubular template by anodization process. Second, modification of the tube diameter of the oxide template by a chemical etching process. Third, preparation of an Al_xIn_1-xSb bulk with a desire composition. Binary and ternary alloys were prepared from powders of aluminum, indium and antimony by melting the elements with small sealed quartz tube in tube furnace under an argon atmosphere. Fourth, the entire chamber was vacuumed and heated up to melt the Al_xIn_1-xSb bulk, then load 50 kgf / cm² for 5 min to press melting filling a liquid phase of Al_xIn_1-xSb into the AAO template to form Al_xIn_1-xSb nanowires. Finally, the entire chamber was cooled down under air atmosphere. Fifth, the AAO were removed by 1.8 wt.% chromic acid (H₂CrO₄) + 6 vol.% phosphoric acid (H₃PO₄) solution at 60 °C for 40 minute, and subsequently, the residual H₂CrO₄, H₃PO₄ solution were cleaned with de-ionized water three times then stored in alcohol solution for further processing and characterization. Moreover, the diameter of Al_xIn_1-xSb NW can be tuned by using the different AAO pore size. The length of the nanowire depends on the fluid properties of the material and the pressure of the hydraulic machine. These as-prepared nanowires were characterized by field-emission scanning electron microscope (FE-SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffractometer (XRD), and transmission electron microscope (TEM) about the morphology, composition, crystal structure and defect. SEM image shows the diameter of nanowire has a good agreement with AAO pore size 100 nm and the length of nanowire is about 10~30 µm. SEM-EDX demonstrates the Al_xIn_1-xSb bulk has precise stoichiometric composition. However, due to the nanowires were placed on the Si Substrate, characteristic X-ray spectra of aluminum and silicon are too close cause the influence of peak overlapping. On the other hand, the TEM substrate (copper grid with carbon film) is proper to utilize. Therefore, the composition of nanowire was investigated by TEM-EDX and STEM mapping. In the TEM analysis, both of the high resolution image and diffraction pattern can prove the presence of lattice strain, and it reflects that the aluminum successfully is substituted for indium. Furthermore, Scanning Transmission Electron Microscope (STEM) mapping shows good uniformity of the whole ternary nanowire. In the future, Fourier transform infrared spectroscopy (FTIR) will be used to determine the band gap Al_xIn_1-xSb NWs and fabrication of device by using focused-ion-beam to carry out electrical measurement.

Reference

[1] Cheng-Hsiang Kuo, Jyh-Ming Wu, Su-Jien Lin, “Room temperature-synthesized vertically aligned InSb nanowires: electrical transport and field emission characteristics”, Nanoscale Research Letters, 2013, 8, 69.

[2] Youwen Yang, Liang Li, Xiaohu Huang, Guanghai Li, Lide Zhang, “Fabrication and optical property of single-crystalline InSb nanowire arrays”, Journal of Materials Science, 2007, 42, 2753-2757.

[3] D. L. Rode, “Electron Transport in InSb, InAs, and InP”, Phys Rev B, 1971, 3, 3287-3299.