Direct Observation of Transient Surface Species during Ge Nanowire Growth and Their Influence on Growth Stability

Abstract

Surface adsorbates are well-established choreographers of material synthesis, but the presence and impact of these short-lived species on semiconductor nanowire growth are largely unknown. Here, we use infrared spectroscopy to directly observe surface adsorbates, hydrogen atoms and methyl groups, chemisorbed to the nanowire sidewall and show they are essential for the stable growth of Ge nanowires via the vapor-liquid-solid mechanism. We quantitatively determine the surface coverage of hydrogen atoms during nanowire growth by comparing ν(Ge-H) absorption bands from operando measurements (i.e., during growth) to those after saturating the nanowire sidewall with hydrogen atoms. This method provides sub-monolayer chemical information at relevant reaction conditions while accounting for the heterogeneity of sidewall surface sites and their evolution during elongation. Our findings demonstrate that changes to surface bonding are critical to understand Ge nanowire synthesis and provide new guidelines for rationally selecting catalysts, forming heterostructures, and controlling dopant profiles.

Progress in doping semiconductor nanowires during growth

“…The primary effects are due to (1) changes in supersaturation with dopant introduction and/or (2) changes to the NW surface energy due to the dopant precursor or its decomposed by-products. 49 It has been reported that the Si NW nucleation could be completely inhibited with high phosphine-to-silane ratios, 50 and similar results were also observed in arsine (AsH3) 51 or trimethylantimony (TMSb) 52 doped Si NWs.…”

Drastic Changes in Material Composition and Electrical Properties of Gallium-Seeded Germanium Nanowires

“…[29][30] The 〈110〉 growth direction of small diameter group IV NWs has been attributed to energy contributions of side facets; [31][32] however, the contributions of side-wall adsorption of decomposition products cannot be ruled out and variations of adsorbates on side facets have been described to cause changes in growth direction. [33][34][35] Therefore, the changes in growth direction with temperature cannot be assigned unequivocally to size effects, even though the same DPG precursor results in different preferred growth directions upon changes in NW diameter. 30 EDX-maps for these NWs do not show any preferential Ga incorporation in the NWs (Figure 2c).…”

Phononic pathways towards rational design of nanowire heat conduction

“…In addition to controlling the surface roughness of the nanowire boundaries, surface chemistry provides another mechanism to engineer phonon scattering at the boundaries and control the thermal conductivity of nanowires [115]. It was observed that HF etching followed by surface hydrogenation could provide nanowires with higher thermoelectric efficiency due to reduced thermal conductivities via boundary impurities [116].…”