|About this Abstract
||2010 Electronic Materials Conference
||TMS 2010 Electronic Materials Conference
||LATE NEWS: W7, Transport Modulation in Ge/Si Core/Shell Nanowires through Controlled Synthesis of Doped Si Shells
||Yanjie Zhao, Joshua Smith, Joerg Appenzeller, Chen Yang
|On-Site Speaker (Planned)
The design and rationale synthesis of nanomaterials with well-defined electronic properties are central for the development of novel nanoelectronics. Developing Ge/Si core/shell nanowires with doped shells can be critical for enabling new nanoelectronic concepts, such as tunneling nanowire field effect transistors for low power applications. Here we report a rational synthesis of the Ge/Si core/shell nanowires with doped Si shells. We demonstrate that the morphology, thickness, and doping of the Si shell can be controlled by tuning growth parameters during the synthesis. We also present electronic characterization of synthesized Ge/Si core/shell nanowires with amorphous and crystalline n-doped Si shells. Ge/Si core/shell nanowires were prepared using the Au nanoparticle mediated chemical vapor deposition method. Radial growth of the Si shell was achieved following the axial growth of the Ge core by altering the synthetic conditions to favor vapor-phase deposition on the Ge surface. The growth temperature was found to be a critical parameter for controlling the morphology of the Si shell. A shell growth at 470°C led to a completely amorphous shell while a growth at 600°C produced a crystalline shell. The Si shell can be selectively doped during the growth by introducing dopant precursor gases. The study on growth of p-doped, n-doped and intrinsic Si shells indicates that the addition of dopants has a strong effect on the growth rates of shells, resulting from the presence of B2H6/PH3 enhancing/suppressing the thermal decomposition of SiH4. Effective activation energy estimated based on growth rates of i-Si at different temperatures is in a good agreement with activation energy of SiH4 thermal decomposition reported, indicating that promoted thermal decomposition at higher temperature is a main contributing factor to the increase in growth rates. Vastly different electrical characterization results between nanowires with different shell morphologies have been observed. Data taken from the nanowires with amorphous doped shells exhibits p-type semiconducting transport and a low electron current at large positive Vgs. The estimated bandgap and the hole mobility value are consistent with the bulk values of Ge. Collectively we conclude that Ge core is the predominant transport path and no significant current contribution is from Si shell. In contrast, the nanowire with crystalline n-Si shell exhibited a small positive slope of Id-Vgs and the high current levels in the subthreshold characteristics indicate a highly conductive n-type channel which is consistent with expectations for conduction through a thin, highly doped crystalline silicon shell.