Method for electrical characterization of nanowires

Abstract

The ability to control conductivity in semiconductor nanostructures is often challenged by surface states trapping the majority of the charge carriers. Addressing this challenge requires a reliable method for assessing electrical properties such as carrier concentration and mobility. Unfortunately, here we are facing another challenge, as the Hall effect is geometrically inapplicable to nanowires while the field effect model is also challenged by the geometry of the common nanowire field effect transistor, and can only yield channel mobility which is very different from Hall mobility. In this paper, we propose a method that combines resistivity and photovoltage measurements with a chemical perturbation to the surface to measure carrier concentration and mobility, as a function of wire diameter, and also to measure the surface state density and the surface band bending before and after the chemical treatment. We apply this method to CVD grown GaN nanowires, before and after a mild HCl etch. Using transmission electron microscope and x-ray photoelectron spectrometry we find that HCl removes the native gallium oxide. The etch is found to reduce the surface state density from 1 × 10(12) to 5.3 × 10(11) cm(2), which is calculated from a reduction of the critical radius for full depletion from 7.6 to 4 nm, and a reduction of the surface band bending from 0.53 to 0.29 eV, observed using surface photovoltage. On the average, the values of carrier concentration we obtain are about ten times smaller, and the mobility about ten times greater, than values obtained using field effect transistors. Interestingly, the weak size dependence of the mobility disappears after etching, suggesting a causal linkage between the as-grown size dependence of the mobility and the density of surface states. The proposed method provides an experimental handle to the study of surface states and their effects on the electrical properties of nanowires.

Radial Stark Effect in (In,Ga)N Nanowires

“…As shown in Ref. 58, hydrochloric acid (HCl) removes the native Ga oxide from the nanowire surface, leading to a reduction of both the surface state density and the surface band bending. The nanowire emission measured right after a 30 s HCl etching exhibits a blueshift of 85 meV.…”

Simultaneous Optical and Electrical Characterization of GaN Nanowire Arrays by Means of Vis-IR Spectroscopic Ellipsometry

“…While the optical characterization of GaN nanowire and nanorod arrays through spectroscopic ellipsometry (SE) 9,10 , polarized-goniometry 20 or reflectivity spectroscopy 11 is well reported in the literature, the characterization of electrical properties related to conductivity, like carrier concentration and mobility, presents some difficulties associated to the geometry of this kind of structures 4,21 . Up to now, the majority of the studies are focused on Hall effect and field effect measurements performed on single nanowires after fabricating multiple contacts [22][23][24][25] .…”

Surface properties of semiconductors from post-illumination photovoltage transient

“…To use it on nanostructures, the specific structure has to be considered. For example, to characterize nanowires, we need to consider a cylindrical structure of radius R. [25] It can be shown that the electric field at the surface is given by…”