Crystal defects in unintentionally doped ZnO nanowires grown by chemical bath deposition (CBD) play a capital role on their optical and electrical properties, governing the performances of many nanoscale engineering devices. However, the nature of these crystal defects is still highly debated. In particular, the hydrogen-related defects have not been explored in detail yet although the growth medium operates in aqueous solution. By using four-point probe resistivity measurements, we show that ZnO nanowires grown by CBD using zinc nitrate and hexamethylenetetramine exhibit a high electrical conductivity with electron densities ranging from 2.7 x 10 18 to 3.1 x 10 19 cm -3 . Most of them have a metallic electrical conduction. By combining density-functional theory calculations with cathodoluminescence and Raman spectroscopy, we reveal that the high electrical conductivity mostly originates from the formation of interstitial hydrogen in bond-centered sites (HBC) and of zinc vacancy -hydrogen (VZn-nH) complexes. In particular, the HBC and (VZn-3H) complex are found to act as two shallow donors with a very low formation energy, for which the most stable configurations are reported. Additionally, this combined theoretical and experimental approach allows us to revisit the highly debated origin of the visible and ultra-violet emission bands in the luminescence spectra. They are found to be mostly related to VZn and (VZn-nH) complexes located in the bulk and on the surfaces of ZnO nanowires. These findings represent an important step forward in the identification of the predominant native and extrinsic defects driving the electronic structure properties of ZnO nanowires grown by CBD. They further reveal the significance of hydrogen engineering to tune the source of crystal defects for optimizing the physical properties of ZnO nanowires.

The chemical bath deposition (CBD) of ZnO nanowires is of high interest, but their formation occurs in a growth medium containing a large number of impurities including carbon, nitrogen, and hydrogen, rendering the accurate determination of predominant crystal defects as highly debated. In addition to the typical interstitial hydrogen in bond-centered sites (H BC ) and zinc vacancy -hydrogen (V Zn -nH) complexes, we reveal that the nitrogen-related defects play a significant role on the physical properties of unintentionally-doped ZnO nanowires. In particular, we show by density-functional theory that the (V Zn -N O -H) defect complex acts as a deep acceptor with a relatively low formation energy and exhibits a prominent Raman line at 3078 cm -1 along with a red-orange emission energy of around 1.82 eV in cathodoluminescence spectroscopy. The nature and concentration of the nitrogen-and hydrogen-related defects are found to be tunable using thermal annealing under oxygen atmosphere, but a rather complex, fine evolution including successive formation and dissociation processes is highlighted as a function of annealing temperature. ZnO nanowires annealed at the moderate temperature of 300 °C specifically exhibit one of the smallest free charge carrier density of 5.6 x 10 17 cm -3 along with a high mobility of about 60 cm 2 /V s following the analysis of longitudinal optical phonon -plasmon coupling. These findings report a comprehensive diagram showing the complex interplay of each nitrogen-and