Understanding the Sensing Mechanism of ZnO Nanoparticles through Identifying Intrinsic Defects

Abstract

Progress in crystal growth made ZnO applicable as the next generation of inorganic lightemitting diodes and lasers, which has attracted much attention. Our previous work is a proof that Zn vacancies are occupied by three protons to form V Zn H 3 complexes in high-quality ZnO single crystals. In this work, electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) studies on high-quality ZnO single crystals further confirm that three proton clusters or cations with three positive charges are the intrinsic defects and/or impurities related to doping in the host-lattice of high-quality ZnO single crystals. Unintentionally doped hydrogen (H) clusters might be relating to ZnO's sensing capabilities. The sensor response of ZnO semiconductors is promoted by a decreasing size; however, the nature of the size effects has not been elucidated satisfactorily. In this work, broccoli-like ZnO nanoarrays, which can detect H 2 S gas in the parts per billion (ppb) region, has been synthesized under a hydrothermal method. High-resolution transmission electron microscopy (HRTEM) experimental results demonstrate that there are multiple polar faces exposed on the surfaces of ZnO nano crystals. The high catalytic active of oxygen species adsorbed on the multiple polar surfaces should respond to the high sensing performance and the high selectivity of ZnO toward reducing H 2 S gas. However, the enormous variations in electric current cannot be produced by releasing electrical charges from O − adsorbates into semiconductors. EPR results show that Zn + interstitials have been produced after the reaction between H 2 S and O − adsorbates on ZnO. In contrast to the unintentionally doped hydrogen (H) clusters, our experimental results show that the Zn + interstitials acting as shallow donors is what really offer the extra free-electron carriers.

Sources of n-Type Conductivity in Single Crystal β-Ga2O3 and Monoclinic WO3 Nanoparticles

“…27 The study of H defects in ZnO single crystals has shown this enormous isotope effect. 28 Protons in −O(H 2 ) groups are accountable for the generation of the W 5+ signal; hence, the H/D exchanging experiments were carried out by soaking the WO 3 samples in D 2 O at 60 °C for 24 h. The EPR spectra in Figure 12 clearly demonstrate that the signal at g = 1.34 is disappeared. This finding is also compatible with the rationale for producing the W 5+ signal.…”

“…The lifetime of a metal oxide semiconductor can be greatly increased by using deuterium instead of hydrogen . The study of H defects in ZnO single crystals has shown this enormous isotope effect . Protons in −O­(H 2 ) groups are accountable for the generation of the W 5+ signal; hence, the H/D exchanging experiments were carried out by soaking the WO 3 samples in D 2 O at 60 °C for 24 h. The EPR spectra in Figure clearly demonstrate that the signal at g = 1.34 is disappeared.…”

Ultrafast and Ultrabroadband UV–vis-NIR Photosensitivity under Reverse and Self-Bias Conditions by n+-ZnO/n-Si Isotype Heterojunction with >1 kHz Bandwidth

“…Isotype heterojunctions have similar majority carriers which contribute to the currents. , As the mobility of holes is much less, a p-p isotype heterojunction is not preferable for high-speed photodetector, whereas a n-n heterojunction would be fruitful. Zinc oxide (ZnO) is one of the most important wide band gap semiconductors for UV photodetector due to its direct band gap, high electron mobility, large exciton binding energy, easy fabrication process, etc. − Due to intrinsic point defects and/or hydrogen impurity, undoped ZnO exhibits n-type conductivity. ,, Fabricating a heterojunction of ZnO with Si would offer a scope to detect light in a broad range from UV to NIR with high efficiency without further doping. The optoelectronic properties of ZnO/Si based p-n heterojunctions have been studied widely but only a few reports are available on isotype heterojunction photodetector based on ZnO/Si.…”

“…22−25 Due to intrinsic point defects and/or hydrogen impurity, undoped ZnO exhibits n-type conductivity. 24,26,27 Fabricating a heterojunction of ZnO with Si would offer a scope to detect light in a broad range from UV to NIR with high efficiency without further doping. The optoelectronic properties of ZnO/Si based p-n heterojunctions have been studied widely but only a few reports are available on isotype heterojunction photodetector based on ZnO/Si.…”