Rational engineering of semiconductor nanowire superstructures

Abstract

Semiconductor nanowire synthesis provides a promising route to engineer novel nanoscale materials for applications in energy conversion, electronics, and photonics. The addition of methylgermane (GeH₃CH₃) to standard GeH₄/H₂ chemistry is demonstrated to induce a transition from <111> to <110> oriented growth during the vapor-liquid-solid synthesis of Ge nanowires. This hydride-based chemistry is subsequently leveraged to rationally fabricate kinking superstructures based on combinations of <111> and <110> segments with user defined angles and segment lengths. The addition of GeH₃CH₃ also eliminates sidewall tapering and enables Ge nanowire growth at temperatures exceeding 475 °C, which greatly expands the process window. User-programmable diameter modulation is demonstrated without kinking using tetramethyltin (Sn(CH₃)₄) or trimethylsilane (SiH(CH₃)₃) reacting directly on the sidewalls of growing nanowires to either block or allow conformal deposition. Catalyst modification with tetramethyltin is demonstrated to tune growth kinetics and provides further control over nanowire design. Morphological markers, generated via user-defined changes to diameter along the nanowire axial direction, enable a new approach to rapid, accurate, and facile extraction of growth rate information from electron microscopy images. The ability to engineer nanowire structure by tuning chemistry either at the nucleation point or on the sidewall is demonstrated in this work, thus enabling the rational fabrication of complex superstructures.