Keywords: nanowire, heterostructure, CVD
Summary:One-dimensional nanomaterials are fundamentals for constructing nanodevices. The function of nanodevice is usually limited by the simple structure of device, such as field effect transistor. Complex circuit can be fabricated by manipulating and connecting multiple nanowires or nanotubes. In order to further improve the function of nanodevice but not enhance the difficulty of device fabrication severely, more one-dimensional nanomaterials are highly desired. Axial nanowire heterostructure may provide more functions and possibilities in applications of nanoelectronic, optoelectronic, and energy conversion. P-n junction is a typical component in modern electronic devices. Nanoscale p-n junction can be formed in a nanowire heterostructure by sequentially growing two different nanowires in axial direction. Some sophisticated techniques are used to grow nanowire heterostructures, such as metalorganic vapor phase epitaxy (MOVPE), molecular beam epitaxy (MBE) and chemical beam epitaxy (CBE). However, synthesis of nanowire heterostructures by chemical vapor deposition (CVD) still remains a challenge. GaAs nanowire usually shows n-type conductivity and p-type GaAsSb nanowire can be formed by Sb doping into GaAs. Therefore, GaAs-GaAsSb nanowire heterostructure may behave as a nanoscale p-n junction. We try to synthesize GaAs-GaAsSb nanowire heterostructures by a two-step CVD method. Si/SiO2 plate covered with gold nanoparticles is used as the substrate. A small amount of GaAs powder is used as the source to grow GaAs nanowires at 750C in the first step. Then the heating unit of tube furnace is turn off and GaSb powder is pushed to the center position of the tube furnace. After the furnace temperature cools down to room temperature naturally, the substrate is taken out and observed. The products show different morphology from common nanowires. One side of the heterostructure is a thin nanowire and the other side is a wide nanobelt. We analyze the structure and composition of the nanowire heterostructure by transmission electron microscopy (TEM). Single crystalline zinc blend structure is found in all length of nanowire heterostructure, whereas a big difference of Sb composition is detected in two sides. One percent and 11% of Sb is detected in the thin nanowire part and the nanobelt side, respectively. Therefore, we conclude that GaAs-GaAsSb nanowire heterostructures are prepared by CVD technique. This result reveals that the simple and cheap CVD technique with solid source is capable of synthesis of nanowire heterostructure.