Synthesis and Properties of Single Crystalline Ge Nanowires

• Main Authors: Tsai, Cheng-Yu, 蔡政佑
• Other Authors: Wu, Wen-Wei
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/47608263586090623633

碩士 === 國立交通大學 === 材料科學與工程學系 === 99 === Intrinsic single-crystalline Ge nanowires and nanosphere chains have been synthesized on Au-coated Si substrates through thermal evaporation and vapor–liquid–solid mechanism. The influence of different growth parameters on Ge nanowires was systematically studied. The size, morphology and density of Ge NWs can be controlled by adjusting carrier gas, growth temperature, and chamber pressure. Single-crystalline Ge nanowire and nanosphere chains grown along [111] were determined by HRTEM and FFT diffraction pattern. Diamond-cubic crystal structure of Ge was also observed from XRD spectrum. Global back-gate intrinsic Ge nanowire field-effect transistors on the Si3N4 dielectric were fabricated through successive steps of e-beam lithography, nickel deposition and lift off. After RTA process, Ni2Ge/Ge/Ni2Ge heterostructure was formed. The electrical transport property was effectively improved by the heterojuction. Orthorhombic Ni2Ge was determined by HRTEM and FFT. The epitaxial relationship between Ge and Ni2Ge were Ge[110]//Ni2Ge[110] and Ge(-1 1 -1)//Ni2Ge(1 -1 -2). The formation process of Ni2Ge was observed through in situ TEM. Ni2Ge grew at a speed of 1.29 nm/s at 550 ℃. The linear growth behavior of the Ni2Ge nanowire along the Ge nanowire indicated that the growth may be interface reaction controlled. From electrical transport properties measurement, we found that the resistivity exhibited a linear relationship with diameter of nanowire. The resistivity of Ge nanowire was much lower than bulk Ge material. From FET property measurement, intrinsic Ge NW showed p-type behavior and field effect hole mobility of 44.3 cm2/Vs. Room temperature photoluminescence spectra of Ge nanowires possessed a broad blue emission around 462 nm, which was attributed to the oxide related defect states. Due to the existence of oxide defects, Ge nanowires were able to detect visible light.