Growth of Germanium Nanowires on a Flexible Organic Substrate

Germanium nanowires (GeNWs) have received extensive attention due to their potential use in electronic, optoelectronic, sensor and other applications. (Heath 2000; Wu and Yang 2000; Hanrath and Korgel 2002; Hanrath and Korgel 2004) (Greytak 2004) The small size, high aspect ratio, and high surface/volume ratio of Ge and other semiconducting nanowires also make them of great fundamental scientific interest. (Jing, Ni et al. 2006; Allen 2007) GeNWs grown via a vapor-liquid-solid (VLS) mechanism in a modified chemical vapor deposition (CVD) process are crystalline. (Dailey 2004) They can be patterned, functionalized, and/or made components of heterostructures for device applications. (Yun 2003; Hanrath and Korgel 2004; Dai 2005; Wang, Chang et al. 2005; Adhikari, Marshall et al. 2006; Pasquier, Mastrogiovanni et al. 2007) Germanium possesses a higher carrier mobility than silicon, as well as a lower nanowire growth temperature when grown using the VLS method (Adhikari, Marshall et al. 2007). There would be a large market for flexible electronic and photonic devices if functionality and performance could approach that of conventional solid state devices at a reasonable cost. (Bradley, Gabriel et al. 2003; Bitetti, Marchetti et al. 2007) Polymer films hold great promise as a cost-efficient substrate for potential applications such as those of photovoltaics or display technologies, due in large part to their ease of manufacturing, low cost, and extensive past development. Other complex materials combinations are being explored including integrating inorganic nanoparticles or small molecule organics with polymers. Two classes of methods for integrating semiconductor nanowires with flexible materials are: (i) transferring wires from a sacrificial growth substrate to a new material via contact printing or solution deposition (Bradley, Gabriel et al. 2003; McAlpine, Friedman et al. 2003; Saran, Parikh et al. 2004; Fan, Ho et al. 2008), and (ii) direct integration via solution growth or very low temperature VSS growth. (Gibson 2005; Lin 2005; Kang 2008) In the former method nanowires must first be grown on some other substrate and then harvested. However, for many large-scale applications direct growth would be highly preferable. Growing nanowires on the polymer substrates simplifies the processing of any devices through reduction of the number of