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Author: M S Ramachandra Rao Publisher: Springer Science & Business Media ISBN: 813221160X Category : Science Languages : en Pages : 377
Book Description
ZnO has been the central theme of research in the past decade due to its various applications in band gap engineering, and textile and biomedical industries. In nanostructured form, it offers ample opportunities to realize tunable optical and optoelectronic properties and it was also termed as a potential material to realize room temperature ferromagnetism. This book presents 17 high-quality contributory chapters on ZnO related systems written by experts in this field. These chapters will help researchers to understand and explore the varied physical properties to envisage device applications of ZnO in thin film, heterostructure and nanostructure forms.
Author: M S Ramachandra Rao Publisher: Springer Science & Business Media ISBN: 813221160X Category : Science Languages : en Pages : 377
Book Description
ZnO has been the central theme of research in the past decade due to its various applications in band gap engineering, and textile and biomedical industries. In nanostructured form, it offers ample opportunities to realize tunable optical and optoelectronic properties and it was also termed as a potential material to realize room temperature ferromagnetism. This book presents 17 high-quality contributory chapters on ZnO related systems written by experts in this field. These chapters will help researchers to understand and explore the varied physical properties to envisage device applications of ZnO in thin film, heterostructure and nanostructure forms.
Author: Magnus Willander Publisher: CRC Press ISBN: 9814411337 Category : Technology & Engineering Languages : en Pages : 234
Book Description
Zinc oxide (ZnO) in its nanostructured form is emerging as a promising material with great potential for the development of many smart electronic devices. This book presents up-to-date information about various synthesis methods to obtain device-quality ZnO nanostructures. It describes both high-temperature (over 100° C) and low-temperature (under 100° C) approaches to synthesizing ZnO nanostructures; device applications for technical and medical devices, light-emitting diodes, electrochemical sensors, nanogenerators, and photodynamic therapy; and the concept of self-powered devices and systems using ZnO nanostructures. The book emphasizes the utilization of non-conventional substrates such as plastic, paper, and textile as new platforms for developing electronics.
Author: Hatim Alnoor Publisher: Linköping University Electronic Press ISBN: 9176854817 Category : Languages : en Pages : 96
Book Description
One-dimensional (1D) nanostructures (NSs) of Zinc Oxide (ZnO) such as nanorods (NRs) have recently attracted considerable research attention due to their potential for the development of optoelectronic devices such as ultraviolet (UV) photodetectors and light-emitting diodes (LEDs). The potential of ZnO NRs in all these applications, however, would require synthesis of high crystal quality ZnO NRs with precise control over the optical and electronic properties. It is known that the optical and electronic properties of ZnO NRs are mostly influenced by the presence of native (intrinsic) and impurities (extrinsic) defects. Therefore, understanding the nature of these intrinsic and extrinsic defects and their spatial distribution is critical for optimizing the optical and electronic properties of ZnO NRs. However, identifying the origin of such defects is a complicated matter, especially for NSs, where the information on anisotropy is usually lost due to the lack of coherent orientation. Thus, the aim of this thesis is towards the optimization of the lowtemperature solution-based synthesis of ZnO NRs for device applications. In this connection, we first started with investigating the effect of the precursor solution stirring durations on the deep level defects concentration and their spatial distribution along the ZnO NRs. Then, by choosing the optimal stirring time, we studied the influence of ZnO seeding layer precursor’s types, and its molar ratios on the density of interface defects. The findings of these investigations were used to demonstrate ZnO NRs-based heterojunction LEDs. The ability to tune the point defects along the NRs enabled us further to incorporate cobalt (Co) ions into the ZnO NRs crystal lattice, where these ions could occupy the vacancies or interstitial defects through substitutional or interstitial doping. Following this, high crystal quality vertically welloriented ZnO NRs have been demonstrated by incorporating a small amount of Co into the ZnO crystal lattice. Finally, the influence of Co ions incorporation on the reduction of core-defects (CDs) in ZnO NRs was systematically examined using electron paramagnetic resonance (EPR).
Author: Sheng Chu Publisher: ISBN: 9781124939742 Category : Light emitting diodes Languages : en Pages : 107
Book Description
Optoelectronics devices based on ZnO thin films and nanostructures are discussed in this dissertation. A ZnO homojunction LED was demonstrated. Sb-doped p-type ZnO and Ga-doped n-type ZnO on Si (100) substrate were used for the LED device. After achieving ohmic contacts on both types of ZnO, the device showed rectifying current-voltage (I-V) characteristics. Under forward bias, the device successfully showed ultraviolet emissions. The emission properties were analyzed and the emission was confirmed to come from ZnO near band edge emissions. Further analysis showed that the emission mainly comes from the p-type layer of the device. A ZnO ultraviolet laser diode was fabricated and demonstrated. The device consists of Sb-doped p-type ZnO layer and Ga-doped n-type ZnO layer. In between p-layer and n-layer, a thin MgZnO/ZnO/MgZnO quantum well structure was inserted. In this device, random lasing mechanism plays an important role. When the diode was biased, the generation of light was enhanced by the carrier localization effect from the quantum well. The light was scattered between the ZnO random grain boundaries. Since the scattering effect can be so intense that some of the light can return to its original place to form close travel loop, as "random laser cavity". As long as the gain can overcome loss from scattering and material loss, lasing action can be demonstrated. An improved ZnO LED device was grown and characterized. The device grown on c-plane sapphire substrate can favor ultimate device applications due to the improved crystal quality of ZnO and the possibility of getting single crystallinity. A double heterostructure (MgZnO/ZnO/MgZnO) was also inserted in between p-layer and n-layer of the device to enhance the light output. The device showed much enhanced output power of 457 nW, which is two orders stronger than the LED fabricated on Si substrate. The optimization of high quality ZnO thin film on c-plane sapphire substrate was discussed. The devices in chapter two, three and four utilized Si or sapphire substrate, and are all in polycrystalline nature. To solve this problem and get the basis of high output power LEDs and lasers, single crystalline, two dimensional surface ZnO thin films were grown in chapter five. MgO/ZnO double buffer layers were used to accommodate the lattice mismatch. MgO thickness was found to be very important in achieving good ZnO thin film. An optimized growth also yields low background electron concentration and high mobility, which can enable future high quality p-type ZnO engineering. Our research was also expanded from ZnO thin films to ZnO nanostructures. The purpose of chapter six is to demonstrate a ZnO nanowire laser. ZnO nanowires are an excellent cavity and itself is a great gain material. We expanded Sb-doped p-type ZnO from thin films to ZnO nanowires. A p-type ZnO nanowire/n-type ZnO thin film p-n junction was achieved. The device showed lasing action when injection current was larger than ~50 mA. The lasing mechanism and gain/feedback were also discussed in detail.
Author: Augustine Che Mofor Publisher: Cuvillier Verlag ISBN: 3736922868 Category : Technology & Engineering Languages : en Pages : 138
Book Description
Since ZnO resurfaced as a very promising semiconductor material for applications in microelectronics, optoelectronics, sensor technology, biomedicine and spin electronics, producing high purity ZnO nanostructures for such applications has rather proven to be challenging. This book first revises the main properties of ZnO as a semiconductor and nanomaterial and also some fabrication techniques for nanostructures. It later concentrates on the development of a vapour transport system for the growth of high quality ZnO nanostructures (mainly nanorods). The book attempts to explain the influence of reactor pressure, growth temperature and growth time on the morphology and quality of ZnO nanorods. While intrinsic (undoped) ZnO nanorods were grown for extensive analysis, transition metal-doped ZnO nanorods were also fabricated and investigated for possible applications in magnetoelectronics/spintronics. Conventional material characterisation methods are also revisited and employed to analyse the crystalline quality, optical, electrical and magnetic properties of ZnO nanorods. Since the book is writtenin an application-oriented fashion, it extends to the fabrication of ZnO nanrorod-based device structures. Here, nano p-n junctions and nano ZnO/ZnMgO quantum well structures are also presented. At the end, the reader clearly sees how ZnO nanorods of extremely high crystalline quality can be grown using an unconventional technique.
Author: Zhe Chuan Feng Publisher: Taylor & Francis ISBN: 1439855757 Category : Science Languages : en Pages : 563
Book Description
Through their application in energy-efficient and environmentally friendly devices, zinc oxide (ZnO) and related classes of wide gap semiconductors, including GaN and SiC, are revolutionizing numerous areas, from lighting, energy conversion, photovoltaics, and communications to biotechnology, imaging, and medicine. With an emphasis on engineering a
Author: Vladimir Petukhov Publisher: Cuvillier Verlag ISBN: 373694084X Category : Science Languages : en Pages : 112
Book Description
For the electronic and optoelectronic device realization a precise control of the electrical properties in the utilized material is a very important issue. Doping profiles in realized p-njunctions influence the functionality of the devices. The morphological and crystal properties of a device material directly influence the electrical ones. Dislocations present in a region of p-n-junctions can short circuit them leading to malfunctions. Too rough surfaces during epitaxial growth could lead to inhomogeneities in a single or multiple quantum wells and superlattices. The main goal of the present work was to provide the basis for a reliable p-type doping of ZnO grown by molecular beam epitaxy. Firstly, the well established heteroepitaxial growth on c-sapphire substrates has been employed. Based on the theoretical and experimental works, suggesting nitrogen to be the impurity that builds the most shallow acceptor level in ZnO comparing to other group-V elements, it has been implied as a dopant. To generate reactive nitrogen atoms an rf-plasma source has been utilized in the MBE process. The resulting samples have been characterized by such methods as AFM, XRD, TEM, PL spectroscopy, temperature domain Hall measurements (TDHM) and ECV-profiling. First results of TDHM have shown that even in undoped samples the temperature dependencies of the electron mobility and carrier concentration have regions which are difficult to interpret. It is necessary to fit them with theoretical curves in order to extract the correct values. This task has proven to be very difficult. The complicated character of the dependencies has been explained in terms of the multilayer conduction model dividing a layer in thin interfacial region with mobility and carrier concentration μ1 and n1 respectivly and bulk region with a higher mobility μ2 and lower carrier concentration n2. The electrical transport in the bulk region has been modeled in terms of the general scattering theory in polar semiconductors. Such scattering mechanisms as scattering on polar-optical phonons, piezoelectric phonons, acoustic deformation potential, strain induced fields, dislocations, ionized and neutral impurities have been taken into account. Two cases have been considered to model transport in the interfacial region: 1) transport takes place in the conduction band of a highly doped degenerate semiconductor; 2) transport takes place in the impurity band formed by intermediate concentration of impurities and in conduction band in parallel. In the second case transport at the interface in conduction band has been neglected in the region of the low temperatures due to the impurities freeze-out and carrier concentration has been taken temperature independent like in the first case. To investigate experimentally the transport character in these two regions independently a mobility-spectrum analysis has been conducted. Theoretical results utilizing the two models have been compared with experimentally extracted mobility and carrier concentration in the interfacial region. It has been concluded that the concentration of donors in the layers is not high enough for the impurity band to merge with the conduction band and the second model is more consistent. The theoretically acquired donor concentration profiles have been compared with ECV-profiles. The agreement is very good. Simulations have revealed a shallow donor state with the ionization energy of approximately 45 meV . In the literature, this donor state in ZnO is attributed to hydrogen. However, due to the high diffusion mobility of hydrogen in ZnO, an annealing process would obviously decrease the carrier concentration in the samples which has not been the case. It has been suggested that the main donor centers are the electrically active crystal point defects generated by dislocations. Layers doped with nitrogen have been grown at very low temperatures (≈ 200°C) and at temperatures ranging from 400°C to 500°C, which are optimal for the epitaxial growth of ZnO. The samples grown at low temperatures are single crystalline with mosaic structure. In both cases, the introduction of the dopant increased the carrier concentration. This has been accounted for a bad crystal quality resulting in the inhomogeneous incorporation of nitrogen and for high background donor concentration due to the high dislocations densities. Additionally, the incorporation of acceptor centers shifts the Fermi-level increasing the formation probability of the compensating point defects. The analysis of TDHM showed an inconsistency of the one donor level model in the case of nitrogen doped samples. This fact and the decrease in the carrier concentration after annealing at 800°C for 30 minutes in ambient air can be explained by nitrogen forming donor-like defect complexes. In an attempt to improve the crystal quality of the heteroepitaxial layers, 15 periods of a ZnO/Zn0.6Mg0.4O superlattice structure have been inserted between the conventional double HT-MgO/LT-ZnO buffer and a main HT-ZnO layer. TDHM has revealed a very high mobility close to the values measured in a bulk ZnO for the temperature range of 20 - 300 K. However, TEM investigations of the samples have not indicated any decrease in the dislocation density comparing with the similar samples without a superlattice. Such a high mobility has been attributed to an electron transport in the superlattice structure. Heteroepitaxial growth of high quality ZnO-layers has proven to be challenging leaving the homoepitaxial growth as the only possibility to obtain the epitaxial layers with the best structural and electrical properties. The hydrothermally grown bulk ZnO substrates from two supplying companies, CrysTec and TokyoDenpa, have been employed for homoepitaxy. The substrates from CrysTec have not been epi-ready. Although AFM images reveal very flat surface, this has been damaged by the process of the chemomechanical polishing. This damaged layer must be removed. This has been achieved by the thermal annealing for 3 hours at 1050°C in ambient air. The thermally treated surfaces resulted in atomically flat terraces. XRD measurements have indicated an improvement of the crystal quality after annealing. The resistivity of the bulk substrates decreased after the thermal treatment due to out-diffusion of the compensating Li atoms letting Al, Ga and In atoms to contribute to conduction. After the longer annealing processes the etch-pits have been discovered on O-polar faces. The same features could be achieved by the chemical etching in a nitric acid on Zn-polar faces. The density of the threading dislocations on both polar faces for both types of substrates calculated by the etch-pit density investigation is about 105 1/cm2. Further the thermally treated substrates with atomically flat terraces have been utilized for homoepitaxy. The differences in growth kinetics during the molecular beam epitaxy on such substrates with the improved surface quality depending on their polarity have been investigated by RHEED measurements. The growth on a Zn-polar face has a 3D-character independently on a supplier. Morphologies of the resulting O- and Zn-polar layers have shown to be different. This has been explained by the presence of dangling bonds on Opolar face and thus, shorter diffusion time of the impinging Zn atoms on the surface. XRD and TEM measurements have shown a perfect crystal quality of the overgrown layers. The PL spectra of homoepitaxial layers are governed by the donor impurities diffused from the substrates. Considering the SIMS measurements of homoepitaxial layers found in the literature it has been concluded that the diffusion of donors in the layers grown on Zn-polar faces takes less effect then for the O-polar films. This conclusion has enforced the utilization of Zn-polar substrates supplied by CrysTec for the experiments with nitrogen doping of ZnO because of their affordable price. The electrical properties measured by ECV-profiling in series of homoepitaxial layers with varied growth parameters have shown an increase of the carrier concentration with the nitrogen incorporation. In addition, it has also been shown that the resulting electrical properties near the interface are governed mostly by the initial properties of the substrates. With increasing thickness of the layers carrier concentration saturated to the values of around 1016 1/cm3. The recent successful realization of the p-type MgZnO layers on TokyoDenpa substrates by researchers from Japan suggests switching to the p-type doped alloys because the above discussed results indicate that p-type doping with nitrogen of a pure ZnO is very difficult or even impossible. This is due to a rather fundamental reason: the formation of the compensating donor centers with the incorporation of acceptor atoms. As the first step in the future works, it is obvious to try to reproduce the results of the ZnMgO p-type doping with nitrogen employing growth on ZnO substrates.
Author: M S Ramachandra Rao
Author: M S Ramachandra Rao
Author: Magnus Willander
Author: Hatim Alnoor
Author: 
Author: Abdelhamid Abdelrehim Mahmoud Elshaer
Author: Sheng Chu
Author: Augustine Che Mofor
Author: Maximilian Kolhep
Author: Zhe Chuan Feng
Author: Vladimir Petukhov