Min-Ki Kwon

Postgrowth In Situ Chlorine Passivation for Suppressing Surface-Dominant Transport in Silicon Nanowire Devices

We demonstrate a postgrowth in situ chlorine passivation method for suppressing surface-dominant transport in Si nanowires (SiNWs). This scheme helps avoid misorientations and meandering while facilitating the passivation of surface states. The leakage current of bridged SiNWs exhibited close to five orders of magnitude reduction as a result of chlorine passivation. The micro-Raman spectroscopy clearly reveals the nature of the varieties of silicon-chlorine bonds of the passivated devices. The chlorine-passivated SiNW surfaces are found to be stable over a long period of time with high immunity to environmental degradation. The chlorine passivation implies an effective and reliable method that can be tailored for mass manufacturing of nanowire-based devices.

Waveguide-integrated nanowire photoconductors on a non-single crystal surface

The growth of crystalline 1D nanowires of semiconductors on non-epitaxial surfaces holds the promise to overcome many of the current challenges of heteroepitaxial material synthesis and device fabrication for a wide range of electronic and photonic applications. Nano-heteroepitaxial bridging of CVD grown nanowires potentially enables a low cost and mass-manufacturable approach to nanowire based device fabrication. Here we report the synthesis and bridging of lateral silicon nanowires between a pair of vertical non-single crystal surfaces and application of this technique in the design and fabrication of waveguide-integrated photodetectors. The device consists of a number of 1D nanowires laterally grown across gaps etched into rib optical waveguides with an amorphous silicon oxynitride core and silicon oxide claddings. A pair of phosphorous-doped polysilicon electrodes was deposited on the walls of the waveguide gap for electrical interfacing of the nanowires to collect the photocurrent under optical excitation. Characterization results demonstrated good waveguide characteristics, high electrical isolation between the electrodes, low leakage current and distinct photoresponse from the bridged nanowires. This implementation of silicon nanowires on polysilicon combines the characteristics of crystalline 1D nanowires with the flexible fabrication processes on non-single-crystal silicon platforms facilitating advances in silicon photonics and beyond.

In-situ chlorine passivation to suppress surface-dominant transport in silicon nanowire devices

We demonstrate a post-growth in-situ chlorine passivation for suppressing surface-dominant transport in Si nanowires (SiNWs). The leakage current of bridged SiNWs suppressed more than five orders of magnitude as a result of chlorine passivation while the shape and structural properties of the bridging NWs remain unaffected by the post-growth in-situ HCl passivation. The chlorine passivated SiNW surfaces were found to be beneficial to enhance the high immunity to environmental degradation.

Temperature-Dependent Structural Characterization of Silicon Nanowires

For high speed and performance field effect transistor with high carrier mobility, vertically aligned Si <110> nanowires is demonstrated by chemical vapor deposition via a vapor-liquid-solid growth mechanism. We found that the orientation of NWs was changed from <111> direction to <110> direction on a Si (110) substrate with increasing the growth temperature above ~ 610°C by changing Au-Si eutectic phase. These vertically aligned <110> oriented SiNWs with significantly high carrier mobility opens up new opportunities for high speed and performance future electronic device applications.

Single crystal semiconductor micropillar and nanowire on amorphous substrates for low cost solar hydrogen generation

We report a novel method to fabricating single crystal and highly oriented 1-D Silicon micropillars and nanowires and then transferring them to coat a target surface of any topology using an innovative harvest/lift-off process. This method enables highly crystalline micro- and nano- pillars of different materials with diverse bandgaps and physical properties to be fabricated on appropriate mother substrates and transferred to form multilayered 3D stacks for multifunctional devices. This approach not only ensures the incorporation of any kind of material (with the best device characteristics) on a single substrate facilitating substrate-free device fabrications on any topology, but also allows the repeated use of a mother substrate for continual production of new devices. This capability of fabricating substrate-less devices will offer a universal platform for material integration and allow solar active devices to be coated on various surface topologies that would be suitable for solar hydrogen generation.