Gate-Tunable Hole Transport in In-Plane Ge Nanowires by V-Groove Confined Selective Epitaxy

Germanium (Ge) nanowires hold great promise as building blocks for hole spin-based quantum processors. Realizing this potential requires their direct integration onto silicon (Si) wafers. This work introduces V-groove-confined selective epitaxy to enable the in-plane growth of nanowires on Si substrates. Nanowires form fully confined within V-shaped grooves, a process driven by surface energy minimization and in agreement with Winterbottom-like construction calculations. This confinement eliminates the direct Ge-SiO2 interface, reducing spurring charge noise and enhancing nanowire functionality. Aberration-corrected scanning transmission electron microscopy reveals the cross-sectional shape and single-crystalline nature of the nanowires. Low-temperature magnetotransport measurements on Ge nanowire Hall bars demonstrate gate-tunable hole densities and a peak mobility of approximately 600 cm(2) V(-1)s(-1) at a density of 1.2 x 10(13) cm(-2). These findings establish V-groove-confined epitaxy as a scalable pathway for the integration of high-performance Ge nanowire-based quantum devices.