Surface Chemistry and Electrical Properties of Germanium Nanowires

Abstract

Germanium nanowires (GeNWs) with p- and n-dopants were synthesized by chemical vapor deposition (CVD) and were used to construct complementary field-effect transistors (FETs). Electrical transport and X-ray photoelectron spectroscopy (XPS) data are correlated to glean the effects of Ge surface chemistry to the electrical characteristics of GeNWs. Large hysteresis due to water molecules strongly bound to GeO(2) on GeNWs is revealed. Different oxidation behavior and hysteresis characteristics and opposite band bending due to Fermi level pinning by interface states between Ge and surface oxides are observed for p- and n-type GeNWs. Vacuum annealing above 400 degrees C is used to remove surface oxides and eliminate hysteresis in GeNW FETs. High-kappa dielectric HfO(2) films grown on clean GeNW surfaces by atomic layer deposition (ALD) using an alkylamide precursor is effective in serving as the first layer of surface passivation. Lastly, the depletion length along the radial direction of nanowires is evaluated. The result suggests that surface effects could be dominant over the "bulk" properties of small diameter wires.

Contactless monitoring of the diameter-dependent conductivity of GaAs nanowires

“…The conductivity of NWs, one of the most important properties exploited in numerous applications, becomes extremely sensitive to the status of the surface with decreasing NW width, and dramatic conductivity changes can be observed when the Debye length becomes comparable to the NW radius [4]. Along with presence of adsorbates and charged surface states [5,6], other factors that may affect the conductivity include the (i) reduced mobility due to enhanced phonon or surface scattering [7,8], (ii) edge effects due to unsaturated bonds of the surface atoms [9], (iii) size-imposed limits to the effective doping concentration [9,10], (iv) size-dependence of depletion width [11], band-gaps [12,13], and recombination barriers [14]. As a result, significant scatter in the conductivity data are observed for individual GaAs NWs purportedly fabricated in the same manner [15].…”

“…Chemical modifications of the surface are another poorly controlled factor that influences the transport properties, since these differ for NWs made of different compound semiconductors [6,17]. Formation of a thin oxide layer is the most common result of exposure to air [6,18] and can lead to band bending and, consequently, to the formation of a depletion layer [19,20].…”

Silicon Vertically Integrated Nanowire Field Effect Transistors

“…2,12 For example, hysteretic behavior of the threshold voltage is commonly observed due to the presence of surface and interface charge-trapping states on the nanowire surface. 3,13 This surface dependence potentially limits the transistor reliability.…”

“…Although this is approximately double the theoretical room temperature limit of 60 mV/decade, it is already much smaller than typical values obtained for nanowire devices with back-gate or top-gate geometries (typically >300 mV/decade, with the minimum reported value to be 140 mV/decade). 2,12,13,30 Further reduction of S can be accomplished by using thinner gate oxides and high-k materials as the gate dielectric, as S values down to 70 mV/ decade have been experimentally shown in lithographically defined vertical transistors. 31 Finally, we have been able to successfully fabricate Si VINFETs with 6.5 nm Si nanowire channel diameters and gate lengths that range from 300 to 350 nm ( Figure S5, Supporting Information).…”

Development of ultra-high density silicon nanowire arrays for electronics applications

“…These include plasmonic effects [5], quantum confi nement effects [6], and phononic effects [7]. In addition, the intrinsically large surface-to-volume ratio characteristic of all NWs provides new scientific opportunities as well [8,9]. These various effects and their associated applications can all be influenced via control over NW dimensions, crystallographic orientation, stoichiometry, surface passivation, doping, etc.…”