Polarity-Dependent High Electrical Conductivity of ZnO Nanorods and Its Relation to Hydrogen

Abstract

A statistical analysis of the electrical properties of selective area grown O- and Zn-polar ZnO nanorods by chemical bath deposition is performed by four-point probe resistivity measurements in patterned metal contact and multiprobe scanning tunneling microscopy configurations. We show that ZnO nanorods with either polarity exhibit a bulklike electrical conduction in their core and are highly conductive. O-polar ZnO nanorods with a smaller mean electrical conductivity have a nonmetallic or metallic electrical conduction, depending on the nano-object considered, while the vast majority of Zn-polar ZnO nanorods with a larger mean electrical conductivity present a metallic electrical conduction. We reveal, from Raman scattering and spatially resolved 5 K cathodoluminescence measurements, that the resulting high carrier density of ZnO nanorods with O or Zn polarity is due to the massive incorporation of hydrogen in the form of interstitial hydrogen in bond-centered sites (HBC), substitutional hydrogen on the oxygen lattice site (HO), and multiple O–H bonds in a zinc vacancy (VZn–H n ). While HBC is largely incorporated in ZnO nanorods with either polarity, HO and (VZn–H n ) defect complexes appear as the dominant hydrogen-related species in O- and Zn-polar ZnO nanorods, respectively. These findings reveal that polarity greatly affects the electrical and optical properties of ZnO nanorods. They further cast a light on the dominant role of hydrogen when ZnO nanorods are grown by the widely used chemical bath deposition technique. This work should be considered for any strategy for thoroughly controlling their physical properties as a prerequisite for their efficient integration into nanoscale engineering devices.

Investigating Size-Dependent Conductive Properties on Individual Si Nanowires

“…5f, the averaged current exhibits more than three times decrease when the length increases from 300 to 960 nm, indicating the nanowires' conductance decreasing with the increased length. The dependence of nanowire resistance on the length has previously been investigated by four-point resistance measurements on semiconductor nanowires, which suggested that under Ohmic contact the nanowire' resistance increased with its length linearly with the slope of resistivity [56,57]. In our case, from the plot of I~1/L as given in Additional file 1: Figure S2, the dependence is remarkably nonlinear; hence, the resistivity could not be correctly obtained from the curve slope.…”

Modeling the Elongation of Nanowires Grown by Chemical Bath Deposition Using a Predictive Approach

“…Also, a partial dehydration of Zn 2+ ions might be sufficient for its direct incorporation onto the c-plane faces of ZnO NWs, leading in turn to a massive incorporation of hydrogen in their center as reported in Ref. 47 . Therefore, the relatively high activation energy we obtain is most likely Ref.…”

Dimensional Roadmap for Maximizing the Piezoelectrical Response of ZnO Nanowire-Based Transducers: Impact of Growth Method

“…In contrast, the range of doping level in ZnO NWs strongly depends on the growth method used, as represented in Figure 3 . From the large number of experimental data reported in the literature using field-effect transistor (FET) measurements [ 30 , 35 , 40 , 44 , 45 , 46 , 47 ], I–V measurements on four-terminal contacted ZnO NWs [ 28 , 29 , 31 , 36 , 37 , 50 ], terahertz spectroscopy [ 34 ], conductive AFM (i.e., SSRM and SCM measurements) [ 32 , 43 ], and electrochemical impedance spectroscopy [ 39 , 41 ], a range of charge carrier density values was inferred for each growth method when ZnO NWs are grown using standard conditions (i.e., typical chemical precursors, typical growth temperature and pressure). Overall, the charge carrier density of ZnO NWs typically lies in the range of 10 17 to 10 20 cm − 3 .…”

“…Overall, it is well-known that ZnO NWs exhibit a high electrical conductivity and thus a high doping level, regardless of the growth method involved [ 28 ]. However, charge carrier density values spread over several decades from 10 17 cm −3 to 10 20 cm −3 [ 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 ]. The main reason is related to a large incorporation of residual impurities (i.e., Al, Ga, In, etc.)…”