Molecular Foundry Seminar

"Synthesis and Defect Control in Bandgap Engineered Ge/Si Nanowire Devices"

Dr. Shadi Dayeh, Center for Integrated Nanotechnologies, Los Alamos National Laboratory
Monday, October 31st at 10:00 am, Bldg. 67 - Rm. 3111

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Abstract:

Understanding the growth processes which combine different materials at an atomic level enables exploring the ultimate limits of device architectures and tailoring materials design for improved device performances. The purpose of this talk is to address the underlying science behind the challenges in controlling structure and morphology in heterostructured nanowires and how this understanding establishes structure-electronic property correlation in Ge/Si heterostructured nanowires. We will first establish key factors in controlling the vapor-liquid-solid growth in semiconductor nanowires and extend those to the growth of radial and axial Ge/Si heterostructure nanowires with an emphasis on the impact of the Au growth seed on their structure and morphology. Our coherently strained Ge/Si core/shell nanowires (rGe=15nm/tSi=2nm) demonstrated a hole ballistic length of ~ 220nm at room temperature and optimizing the Si shell morphology allowed 2X improvement in their HFFET hole mobilities. Heterostructuring in the axial direction is shown to provide a unique fingerprint for tracking fault nucleation and propagation during the VLS synthesis of semiconductor nanowires. In addition, axial heterostructures allow tailoring the band-edge profile along the transport direction in a nanowire device enabling Schottky-barrier HFET devices based on 100% Ge-Si axial nanowires which outperformed their homogenous counterparts by several orders of magnitude in on-currents and on/off ratios. We conclude by comparing how defects in VLS grown compound semiconductor nanowires (InAs) differ in their impact on transport from those in elemental semiconductors (Ge, Si).