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Growth Condition-Oriented Defect Engineering for Changes in Au–ZnO Contact Behavior from Schottky to Ohmic and Vice Versa
摘要： ZnO has the built-in characteristics of both ionic and covalent compound semiconductors, which makes the metal–ZnO carrier transport mechanism quite intricate. The growth mechanism-centric change in ZnO defect density and carrier concentration also makes the contact formation and behavior unpredictable. This study investigates the uncertainty in Au–ZnO contact behavior for application-oriented research and the development on ZnO nanostructures. Herein, we explain the phenomenon for how Au–ZnO contact could be rectifying or non-rectifying. Growth method-dependent defect engineering was exploited to explain the change in Schottky barrier heights at the Au–ZnO interface, and the change in device characteristics from Schottky to Ohmic and vice versa. The ZnO nanorods were fabricated via aqueous chemical growth (ACG) and microwave-assisted growth (MAG) methods. For further investigations, one ACG sample was doped with Ga, and another was subjected to oxygen plasma treatment (OPT). The ACG and Ga-doped ACG samples showed a quasi-Ohmic and Ohmic behavior, respectively, because of a high surface and subsurface level donor defect-centric Schottky barrier pinning at the Au–ZnO interface. However, the ACG-OPT and MAG samples showed a more pronounced Schottky contact because of the presence of low defect-centric carrier concentration via MAG, and the removal of the surface accumulation layer via the OPT process.
关键词： oxygen plasma treatment,nanorod,ZnO,crystal defects,microwave,metal-semiconductor contact
更新于2025-09-23 15:22:29
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External pressure induced liquid crystal defects for optical vortex generation
摘要： Simple and arbitrary creation of liquid crystal (LC) defects can be highly useful, in particular, for the creation of optical vortex. We report a novel method to create an isolated and stable +1 type concentric LC defect by combing an external pressure on a vertically aligned liquid crystal cell (VALC) and the application of electric fields. The method does not require special material in alignment layer, nor patterned electrodes such as in spatial light modulator, but it can produce stable and rewritable defects in a LC cell. We show that the created +1 defect can be used to generate optical vortices with ±2(cid:125) orbital angular momentum. The simple and cost-effective process and its tunability for the position of defect make the method useful in various applications such as advanced optical communication and quantum computation using tunable optical vortices.
关键词： electric fields,orbital angular momentum,liquid crystal defects,optical vortex generation,external pressure
更新于2025-09-23 15:21:01
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A review of <i>β</i> -Ga <sub/>2</sub> O <sub/>3</sub> single crystal defects, their effects on device performance and their formation mechanism
摘要： As a wide-bandgap semiconductor (WBG), β-Ga2O3 is expected to be applied to power electronics and solar blind UV photodetectors. In this review, defects in β-Ga2O3 single crystals were summarized, including dislocations, voids, twin, and small defects. Their effects on device performance were discussed. Dislocations and their surrounding regions can act as paths for the leakage current of SBD in single crystals. However, not all voids lead to leakage current. There’s no strong evidence yet to show small defects affect the electrical properties. Doping impurity was definitely irrelated to the leakage current. Finally, the formation mechanism of the defects was analyzed. Most small defects were induced by mechanical damages. The screw dislocation originated from a subgrain boundary. The edge dislocation lying on a plane slightly tilted towards the (102) plane, the (101) being the possible slip plane. The voids defects like hollow nanopipes, PNPs, NSGs and line-shaped grooves may be caused by the condensation of excess oxygen vacancies, penetration of tiny bubbles or local meltback. The nucleation of twin lamellae occurred at the initial stage of “shoulder part” during the crystal growth. These results are helpful in controlling the occurrence of crystal defects and improving the device performance.
关键词： formation mechanism,crystal defects,β-Ga2O3,device performance
更新于2025-09-19 17:15:36
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Effect of liquid environment on single-pulse generation of laser induced periodic surface structures and nanoparticles
摘要： The effect of a liquid environment on the fundamental mechanisms of surface nanostructuring and generation of nanoparticles by single pulse laser ablation is investigated in a closely integrated computational and experimental study. A large-scale molecular dynamics simulation of spatially-modulated ablation of Cr in water reveals a complex picture of dynamic interaction between the ablation plume and water, which involves rapid deceleration of the ablation plume by water environment, formation and prompt disintegration of a hot metal layer at the interface between the ablation plume and water, lateral redistribution and redeposition of a major fraction of the ablation plume, and eventual formation of smooth frozen surface features. A good agreement between the shapes of the surface features predicted in the simulation and the ones generated in single pulse laser ablation experiments performed for Cr in water supports the mechanistic insights revealed in the simulations. The results of this study suggest that the presence of liquid environment can eliminate the sharp features of surface morphology, reduce the amount of material removed from the target by more than an order of magnitude, and narrow down the nanoparticle size distribution as compared to laser ablation in vacuum. Moreover, the computational predictions of the effective incorporation of molecules constituting the liquid environment into the surface region of the irradiated target and the generation of high vacancy concentrations exceeding the equilibrium levels by more than an order of magnitude suggest a potential for hyperdoping of laser-generated surfaces by solutes present in the liquid environment.
关键词： Laser-Induced Periodic Surface Structures (LIPSS),Generation of Nanoparticles,Crystal Defects,Surface Morphology,Hyperdoping,Molecular Dynamics Simulations,Pulsed Laser Ablation in Liquids
更新于2025-09-19 17:13:59
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Control of the photoluminescence properties of Nd:YAG crystals by laser irradiation
摘要： This paper presents luminescence properties of Nd:YAG crystal defects including oxygen vacancy, O-hole center, F and F+ centers. The Nd:YAG crystal defects have photoluminescence emission peaks in the ~ 350-500 nm range of UV-Vis spectral region. The results show that laser irradiation can control photoluminescence properties of the Nd:YAG crystal samples. Our results can be very important in solid state laser and surface engineering.
关键词： solid state laser,laser irradiation,crystal defects,photoluminescence,Nd:YAG
更新于2025-09-19 17:13:59
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Crystal defects in monocrystalline silicon induced by spot laser melting
摘要： Laser processing of monocrystalline silicon has become an important tool for a wide range of applications. Here, we use microsecond spot laser melting as a model experiment to investigate the generation of crystal defects and residual stress. Using Micro-Raman spectroscopy, defect etching, and transmission electron microscopy, we find no dislocations in the recrystallized volume for cooling rates exceeding jdT=dtj ? 2 (cid:2) 107 K/s, and the samples remain free of residual stress. For cooling rates less than jdT=dtj ? 2 (cid:2) 107 K/s, however, the experiments show a sharp transition to a defective microstructure that is rich in dislocations and residual stress. Moreover, transmission electron microscopy indicates dislocation loops, stacking-fault tetrahedra, and voids within the recrystallized volume, thereby indicating supersaturation of intrinsic point defects during recrystallization. Complementing photoluminescence spectroscopy indicates even three regimes with decreasing cooling rate. Spectra of regime 1 do not contain any defect related spectral lines. In regime 2, spectral lines appear related to point defect clusters. In regime 3, the spectral lines related to point defect clusters vanish, but dislocation-related ones appear. We propose a quantitative model explaining the transition from dislocation-free to dislocation-rich recrystallization by means of the interaction between intrinsic point defects and dislocations.
关键词： monocrystalline silicon,transmission electron microscopy,laser melting,micro-Raman spectroscopy,crystal defects,residual stress,photoluminescence spectroscopy
更新于2025-09-16 10:30:52
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Enhancement of transport properties in single ZnSe nanowire field-effect transistors
摘要： Wide-gap semiconductors are excellent candidates for next-generation optoelectronic devices, including tunable emitters and detectors. ZnSe nanowire-based devices show great promise in blue emission applications, since they can be easily and reproducibly fabricated. However, their utility is limited by deep level defect states that inhibit optoelectronic device performance. The primary objective of this work is to show how the performance of ZnSe nanowire devices improves when nanowires are subjected to a post-growth anneal treatment in a zinc-rich atmosphere. We use low temperature photoluminescence spectroscopy to determine the primary recombination mechanisms and associated defect states. We then characterize the electronic properties of ZnSe nanowire field effect transistors fabricated from both as-grown and Zn-annealed nanowires, and measure an order-of-magnitude improvement to the electrical conductivity and mobility after the annealing treatment. We show that annealing reduces the concentration of zinc vacancies, which are responsible for strong compensation and high amounts of scattering in the as-grown nanowires.
关键词： electrical resistivity,II–VI semiconductors,crystal defects,carrier transport,photoluminescence,carrier mobility,nanowires
更新于2025-09-09 09:28:46