Diameter-dependent dopant location in silicon and germanium nanowires

Abstract

We report studies defining the diameter-dependent location of electrically active dopants in silicon (Si) and germanium (Ge) nanowires (NWs) prepared by nanocluster catalyzed vapor-liquidsolid (VLS) growth without measurable competing homogeneous decomposition and surface overcoating. The location of active dopants was assessed from electrical transport measurements before and after removal of controlled thicknesses of material from NW surfaces by low-temperature chemical oxidation and etching. These measurements show a well-defined transition from bulk-like to surface doping as the diameter is decreased <22-25 nm for nand p-type Si NWs, although the surface dopant concentration is also enriched in the larger diameter Si NWs. Similar diameterdependent results were also observed for n-type Ge NWs, suggesting that surface dopant segregation may be general for small diameter NWs synthesized by the VLS approach. Natural surface doping of small diameter semiconductor NWs is distinct from many top-down fabricated NWs, explains enhanced transport properties of these NWs and could yield robust properties in ultrasmall devices often dominated by random dopant fluctuations.nanoelectronics ͉ surface doping ͉ surface segregation ͉ vapor-liquid-solid growth

Recent Advances on p-Type III-Nitride Nanowires by Molecular Beam Epitaxy

“…Such an effect is attributed to the reduced lattice strain imposed by surface dopants compared to bulk dopants. A similar effect has also been measured in other semiconductor nanowires [42,[45][46][47]73]. The Mg incorporation into InN nanowires thus can be understood through two competing processes: (a) Mg surface desorption at elevated growth temperatures, and (b) enhanced Mg incorporation, due to the lowering of Mg formation energy.…”

“…For example, unwanted defect donors can be greatly reduced in nanowire structures due to efficient strain relaxation to large surface area [41]. Moreover, recent studies indicate that dopants have lower formation energies in nanowire structures, which can significantly enhance dopant incorporation [42][43][44][45][46][47].…”

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“…The mobility values were taken from similar SiNWs with the same device structure, 30 and nonuniform doping was ignored because it is mainly observed when the diameter is below 20 nm. 34 Without any trap states, we input a large range of doping concentrations between 7 Â 10 17 and 7 Â 10 19 cm À3 , but it was not possible to match the 3-D simulation with the measured data in all respects ( Figure S3 in the Supporting Information). On the other hand, the 3-D simulation with the surface trap charges shows well-matched results with the features of the measured data, including the ideality factor, current level, and gate-switching behavior (Figure 4a and 4b).…”

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