Download or read book Heteroepitaxial Growth and Doping of ZnO for Optoelectronic Applications written by and published by . This book was released on 2005 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is the final report of AFOSR grant Number F49620-01-1-0454. No cost extension for one year (31 August/04 to Sept. 1/05) was granted by AFOSR. Summary of the research accomplishments duration the total duration 31 August 2001 - Sept. 1/2005 is presented. C- axis oriented ZnO films and nano rods have been grown by rf sputtering and pulse laser deposition (PLD). Thin films of Znl-xMgxO, Znl-xAlxO, and magnetic ion substituted ZnMO (M= Co, Mn, Fe, Gd) have been investigated. ZnO, ZnCoO, ZnMnO nano-particles have been synthesized which clearly showed quantum confinement effect. MgO/ZnO multilayer and ZnAlO films deposited by PLD showed c-axis growth and wide band gap above -6 eV), which is suitable for UV detectors. Mn, Co, and Fe substituted ZnO and ZnS show nearly similar optical behavior, but ZnMnO showed magnetic behavior by SQUID at 5 K. ZnO films could not be doped p-type by rf sputtering, probably due to very high ionization energy required for nitrogen as p-dopant. Several magnetic ion substituted ZnO showed ferromagnetism at lower temperatures, but ZnxCol-xFe2O4 (0.4

Download or read book Zinc Oxide Materials for Electronic and Optoelectronic Device Applications written by Cole W. Litton and published by John Wiley & Sons. This book was released on 2011-03-23 with total page 403 pages. Available in PDF, EPUB and Kindle. Book excerpt: Zinc Oxide (ZnO) powder has been widely used as a white paint pigment and industrial processing chemical for nearly 150 years. However, following a rediscovery of ZnO and its potential applications in the 1950s, science and industry alike began to realize that ZnO had many interesting novel properties that were worthy of further investigation. ZnO is a leading candidate for the next generation of electronics, and its biocompatibility makes it viable for medical devices. This book covers recent advances including crystal growth, processing and doping and also discusses the problems and issues that seem to be impeding the commercialization of devices. Topics include: Energy band structure and spintronics Fundamental optical and electronic properties Electronic contacts of ZnO Growth of ZnO crystals and substrates Ultraviolet photodetectors ZnO quantum wells Zinc Oxide Materials for Electronic and Optoelectronic Device Applications is ideal for university, government, and industrial research and development laboratories, particularly those engaged in ZnO and related materials research.

Download or read book Zinc Oxide A Material for Micro and Optoelectronic Applications written by Norbert H. Nickel and published by Springer Science & Business Media. This book was released on 2005-12-28 with total page 245 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recently, a significant effort has been devoted to the investigation of ZnO as a suitable semiconductor for UV light-emitting diodes, lasers, and detectors and hetero-substrates for GaN. Research is driven not only by the technological requirements of state-of-the-art applications but also by the lack of a fundamental understanding of growth processes, the role of intrinsic defects and dopants, and the properties of hydrogen. The NATO Advanced Research Workshop on “Zinc oxide as a material for micro- and optoelectronic applications”, held from June 23 to June 25 2004 in St. Petersburg, Russia, was organized accordingly and started with the growth of ZnO. A variety of growth methods for bulk and layer growth were discussed. These techniques comprised growth methods such as closed space vapor transport (CSVT), metal-organic chemical vapor deposition, reactive ion sputtering, and pulsed laser deposition. From a structural point of view using these growth techniques ZnO can be fabricated ranging from single crystalline bulk material to polycrystalline ZnO and nanowhiskers. A major aspect of the ZnO growth is doping. n-type doping is relatively easy to accomplish with elements such al Al or Ga. At room temperature single crystal ZnO exhibits a resistivity of about 0. 3 -cm, an electron mobility of 2 17 -3 225 cm /Vs, and a carrier concentration of 10 cm . In n-type ZnO two shallow donors are observable with activation energies of 30 – 40 meV and 60 – 70 meV.

Download or read book Electrical Characterization of ZnO thin films grown by molecular beam epitaxy written by Vladimir Petukhov and published by Cuvillier Verlag. This book was released on 2012-04-25 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Zinc Oxide written by Claus F. Klingshirn and published by Springer Science & Business Media. This book was released on 2010-07-01 with total page 366 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book gives a comprehensive review of the present state-of-the-art in ZnO R+D, including growth, doping, lattice dynamics, electric magnetic and optical properties. The emphasis is on the electric and optical properties, because this is the area where novel applications may be expected with highest promise. The book highlights not only the most recent results but gives both an overview of past research and of the present status -- not avoiding critical and controversial discussions of various aspects such as bank symmetries and laser processes. Intended to have long-lasting impact on ZnO R+D, this monograph addresses (post-)graduate students but also advanced scientists, who want to embark on ZnO research or are already involved, the present state of the art and assists them in avoiding duplication of old results (or mistakes).

Download or read book Comprehensive Semiconductor Science and Technology written by and published by Newnes. This book was released on 2011-01-28 with total page 3572 pages. Available in PDF, EPUB and Kindle. Book excerpt: Semiconductors are at the heart of modern living. Almost everything we do, be it work, travel, communication, or entertainment, all depend on some feature of semiconductor technology. Comprehensive Semiconductor Science and Technology, Six Volume Set captures the breadth of this important field, and presents it in a single source to the large audience who study, make, and exploit semiconductors. Previous attempts at this achievement have been abbreviated, and have omitted important topics. Written and Edited by a truly international team of experts, this work delivers an objective yet cohesive global review of the semiconductor world. The work is divided into three sections. The first section is concerned with the fundamental physics of semiconductors, showing how the electronic features and the lattice dynamics change drastically when systems vary from bulk to a low-dimensional structure and further to a nanometer size. Throughout this section there is an emphasis on the full understanding of the underlying physics. The second section deals largely with the transformation of the conceptual framework of solid state physics into devices and systems which require the growth of extremely high purity, nearly defect-free bulk and epitaxial materials. The last section is devoted to exploitation of the knowledge described in the previous sections to highlight the spectrum of devices we see all around us. Provides a comprehensive global picture of the semiconductor world Each of the work's three sections presents a complete description of one aspect of the whole Written and Edited by a truly international team of experts

Download or read book ZnO Thin Films for Optoelectronic Applications written by Prasada Rao Talakonda and published by LAP Lambert Academic Publishing. This book was released on 2013 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: Zinc oxide (ZnO) thin films have good electro-optical properties suitable for opto-electronic applications. The present study explains the deposition and characterization of n-type and p-type ZnO thin films by spray pyrolysis. The films were characterized by different methods to understand their structural, optical and electrical properties. Gallium was chosen as the impurity dopant in ZnO films to improve the electrical properties. The electrical conductivity, carrier concentration and mobility of Ga doped ZnO (GZO) films were highly improved in comparison to undoped ZnO films. The GZO films showed good optical transmittance in the visible region. The electrical and optical results suggest that the GZO films are suitable to use as a TCO in optoelectronic industries. The p-type ZnO thin films were successesfully realized using dual acceptor method. The Hall measurements and room temperature photolumiscence results were supported p-type nature of (Li, N): ZnO thin films.

Download or read book Zinc Oxide Materials for Electronic and Optoelectronic Device Applications written by Cole W. Litton and published by John Wiley & Sons. This book was released on 2011-06-07 with total page 403 pages. Available in PDF, EPUB and Kindle. Book excerpt: Zinc Oxide (ZnO) powder has been widely used as a white paint pigment and industrial processing chemical for nearly 150 years. However, following a rediscovery of ZnO and its potential applications in the 1950s, science and industry alike began to realize that ZnO had many interesting novel properties that were worthy of further investigation. ZnO is a leading candidate for the next generation of electronics, and its biocompatibility makes it viable for medical devices. This book covers recent advances including crystal growth, processing and doping and also discusses the problems and issues that seem to be impeding the commercialization of devices. Topics include: Energy band structure and spintronics Fundamental optical and electronic properties Electronic contacts of ZnO Growth of ZnO crystals and substrates Ultraviolet photodetectors ZnO quantum wells Zinc Oxide Materials for Electronic and Optoelectronic Device Applications is ideal for university, government, and industrial research and development laboratories, particularly those engaged in ZnO and related materials research.

Download or read book Zinc Oxide written by Hadis Morkoç and published by John Wiley & Sons. This book was released on 2008-12-03 with total page 488 pages. Available in PDF, EPUB and Kindle. Book excerpt: This first systematic, authoritative and thorough treatment in one comprehensive volume presents the fundamentals and technologies of the topic, elucidating all aspects of ZnO materials and devices. Following an introduction, the authors look at the general properties of ZnO, as well as its growth, optical processes, doping and ZnO-based dilute magnetic semiconductors. Concluding sections treat bandgap engineering, processing and ZnO nanostructures and nanodevices. Of interest to device engineers, physicists, and semiconductor and solid state scientists in general.

Download or read book Processing and Characterization of P Type Doped Zinc Oxide Thin Films written by Michelle Anne Myers and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Applications of zinc oxide (ZnO) for optoelectronic devices, including light emitting diodes, semiconductor lasers, and solar cells have not yet been realized due to the lack of high-quality p-type ZnO. In the research presented herein, pulsed laser deposition is employed to grow Ag-doped ZnO thin films, which are characterized in an attempt to understand the ability of Ag to act as a p-type dopant. By correlating the effects of the substrate temperature, oxygen pressure, and laser energy on the electrical and microstructural properties of Ag-doped ZnO films grown on c-cut sapphire substrates, p-type conductivity is achieved under elevated substrate temperatures. Characteristic stacking fault features have been continuously observed by transmission electron microscopy in all of the p-type films. Photoluminescence studies on n-type and p-type Ag-doped ZnO thin films demonstrate the role of stacking faults in determining the conductivity of the films. Exciton emission attributed to basal plane stacking faults suggests that the acceptor impurities are localized nearby the stacking faults in the n-type films. The photoluminescence investigation provides a correlation between microstructural characteristics and electrical properties of Ag- doped ZnO thin films; a link that enables further understanding of the doping nature of Ag impurities in ZnO. Under optimized deposition conditions, various substrates are investigated as potential candidates for ZnO thin film growth, including r -cut sapphire, quartz, and amorphous glass. Electrical results indicated that despite narrow conditions for obtaining p-type conductivity at a given substrate temperature, flexibility in substrate choice enables improved electrical properties. In parallel, N+-ion implantation at elevated temperatures is explored as an alternative approach to achieve p-type ZnO. The ion implantation fluence and temperature have been optimized to achieve p-type conductivity. Transmission electron microscopy reveals that characteristic stacking fault features are present throughout the p-type films, however in n-type N-doped films high-density defect clusters are observed. These results suggest that the temperature under which ion implantation is performed plays a critical role in determining the amount of dynamic defect re- combination that can take place, as well as defect cluster formation processes. Ion implantation at elevated temperatures is shown to be an effective method to introduce increased concentrations of p-type N dopants while reducing the amount of stable post-implantation disorder. Finally, the fabrication and properties of p-type Ag-doped ZnO/n-type ZnO and p-type N-doped ZnO/n-type ZnO thin film junctions were reported. For the N-doped sample, a rectifying behavior was observed in the I-V curve, consistent with N-doped ZnO being p-type and forming a p-n junction. The turn-on voltage of the device was -2.3 V under forward bias. The Ag-doped samples did not result in rectifying behavior as a result of conversion of the p-type layer to n-type behavior under the n- type layer deposition conditions. The systematic studies in this dissertation provide possible routes to grow p-type Ag-doped ZnO films and in-situ thermal activation of N-implanted dopant ions, to overcome the growth temperature limits, and to push one step closer to the future integration of ZnO-based devices. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/149354

Download or read book Pulsed Laser Deposition of Doped ZnO and Mg Zn O Films for Optoelectronic Applications written by Jean-Marie George Erie and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: ABSTRACT: I analyzed the effects of doping ZnO films with As, N, Nb and Ta and (Mg, Zn)O films by pulsed laser deposition. For the As doped films, photoluminescence and Hall measurements revealed the films were compensated and compensation depended on dopant concentration. The As related acceptor-bound exciton, acceptor binding energy and thermal activation energy was dependent of dopant content and O2 growth pressure. Binding energy of the As related acceptor varied from 190 meV for the ZnO films doped with 0.02 atomic percent of (at %) As to 90 meV for a films doped with 2 at % As. The plot of acceptor optical binding energy against pto the 1/3 suggests that the binding energy at infinite dilution to be approximately 160 meV. The ZnO films doped with 0.2 at % As doped on MgO buffer layer showed the lowest degree of compensation with resistivity, carrier density and mobility on the order of 71 .cm, 2 x 10 to the 16th cm to the negative third power and 2 cm squared/(V.s) respectively. N doped films showed acceptor bound emission and N-acceptor binding energy of 160 meV and N doped ZnO optical binding energy did not show any dependence on film N concentration. The donor-bound exciton emission for the Nd and Ta doped films Ire around 3.31 eV and 3.33 respectively. The Mg0.05Zn 0.95O:As0.002 film grown at 500 degrees Celsius and 60 mTorr showed p-type behavior, where as, the As doped films with higher Mg content were n-type regardless of growth conditions.

Download or read book Handbook of Zinc Oxide and Related Materials written by Zhe Chuan Feng and published by CRC Press. This book was released on 2012-09-26 with total page 449 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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 and materials science, Handbook of Zinc Oxide and Related Materials provides a comprehensive, up-to-date review of various technological aspects of ZnO. Volume One presents fundamental knowledge on ZnO-based materials and technologies. It covers the basic physics and chemistry of ZnO and related compound semiconductors and alloys. The first part of this volume discusses preparation methods, modeling, and doping strategies. It then describes epitaxial methods used to create thin films and functional materials. The book concludes with a review of alloys and related materials, exploring their preparation, bulk properties, and applications. Covering key properties and important technologies of ZnO-based devices and nano-engineering, the handbook highlights the potential of this wide gap semiconductor. It also illustrates the remaining challenging issues in nanomaterial preparation and device fabrication for R&D in the twenty-first century.

Download or read book Molecular Beam Epitaxy Growth and Characerization of ZnO based layers and Heterostructures written by Abdelhamid Abdelrehim Mahmoud Elshaer and published by Cuvillier Verlag. This book was released on 2008-08-21 with total page 144 pages. Available in PDF, EPUB and Kindle. Book excerpt: In semiconductor research a reliable epitaxial growth technique for growing high quality thin films and heterostructures is necessary. In the case of ZnO one of the main difficulties is the absence of suitable substrate material for ZnO epitaxial growth. Although special oxide material (for example ScAlMgO4) and ZnO bulk crystal can serve as lattice matched substrates, the quality of the substrates themselves, the size of the available wafer, and the expense do not encourage to use these lattice matched substrates for ZnO epitaxial growth. In the current research, a widely used low cost commercial substrate sapphire was employed to develop a reliable epitaxial growth technique and growth process for ZnO. The versatile epitaxial growth technique, molecular beam epitaxy (MBE) equipped with a rf-plasma source was developed for growth and various characterizations methods were conducted to obtain a fundamental understanding in both the epitaxial processes and material properties of ZnO thin films and heterostructures. Employing a thin HT MgO buffer layer prior to ZnO growth is the key to overcome the very large mismatches between c-Al2O3 substrate. Wetting the surface of Al2O3 substrate with a few MgO monolayers, lowed the surface energy, so that the lateral growth of ZnO is promoted at the initial growth stage. MgO can be grown in the same chamber as ZnO without any contamination problem. These advantages make the growth procedure of a HT MgO buffer fast and easy. The growth temperature and the growth rate of MgO buffer are found to be important to improve the ZnO heteroepitaxy. An intermediate spinel layer in epitaxial relation with the sapphire substrate as well as with the HT MgO buffer layer is formed in the early stage of growth during the deposition of the MgO at 700°C. It was found that the combination of these two layers is useful for the progressive reduction of the ZnO overgrown with the sapphire substrate.Annealing experiments reveal that as soon as the spinel layer is formed at about 700°C, it remains stable at least up to 1000°C, and even it is extended in thickness. By recording and analyzing RHEED intensity oscillations, the growth kinetics has been investigated. Flat surface morphology and layer-by-layer growth has been achieved. The stoichiometry has been deduced by analyzing the growth rate as a function of Zn and O fluxes for various growth temperatures. It is found that the sticking coefficient of oxygen radicals is less dependent on the substrate temperature than that of Zn. The stoichiometric condition shifts to larger Zn flux at higher growth temperature. The kink rZnO values determine the activated O-flux supplied by the RF plasma source at TS=500°C, 400W and a given O2-flow rate. It equals 0.5±0.05 Ås-1 per sccm. Absolute αZn values versus TS, defined as αZn=rZnO(T)/rZnO(max), where rZnO(max) is recalculated from the Zn flux measured by a quartz monitor, using Zn/ZnO molar mass and density ratios. Ex-situ characterization of the grown ZnO layers indicate that the surface morphology and crystal quality of the ZnO films grown on sapphire by MBE using either oxygen plasma cell or H2O2 as an oxidant can be extensively improved by using an HT MgO buffer. ZnO layers reveal strong variation of surface morphology versus the O/Zn flux ratio. The most flat surface morphology of ZnO is obtained when the ratio is within the 0.7-1 range. The growth under O-rich conditions leads to formation of hexagonal pyramids and at higher O/Zn ratios to a 3D growth with the top layer formed by perfectly c-oriented columnar structures of 50-100 nm in a diameter. It was also possible to recover the initial 3D growth mode to the 2D one by employing the Zn-rich growth conditions at O/Zn=0.4-0.6. Structural characterizations by high resolution X-ray diffraction (HR-XRD) and transmission electron microscopy (TEM) indicate a dramatic reduction in defect density in the ZnO epilayers grown with an HT MgO buffer. By using TEM, it was found that the dominant extending defects are edge, screw and mixed-type dislocations along c-axis. The main defects were threading dislocations. This is resulted from the well controlled layer-by-layer growth, since only the edge-type dislocation is able to accommodate the lattice mismatch, while the screw type dislocation forms much related to the initial nucleation environment.The microstructure of ZnO epilayers has been studied by HR-XRD. The full width at half maximum of the (0002) reflection, 0.007 degree, is much smaller than that of the (10-10) reflection, 0.27 degree revealing the micro-twist dominates the mosaicity, while micro-tilt is much less important.This pronounced difference of the rocking curve widths between the (0002) and (1010) reflections strongly indicates that the density of pure edge threading dislocations is greater than that of pure screw dislocations. Optical characterizations reveal that exciton plays an important role in ZnO. At room temperature free exciton recombinations dominate the photoluminescence. The ZnO epilayers reveal well resolved low temperature PL excitonic spectra with a dominant bound exciton line (3.355 eV) possessing a ~2 meV half-width and a peak of free A exciton at 3.374 eV. The low-energy tail extending from the excitonic emission peaks due to the lattice deformation is significantly reduced, which allows the observation of two electron satellites and LO-phonons replicas of free and bound excitons. Variation of growth stoichiometry from O-rich to Zn-rich results in the pronounced quench of the acceptor-bound part of the excitonic band, as well as the strong intensity redistribution of donor-bound lines which seems to be attributed to a change in the point defect density. Temperature dependence of PL spectra between 6K and room temperature every 30 K under the same excitation conditions was performed. Slowly decreases coming at 300K to about one third of the intensity at 6K. This corresponds to the activation of non-radiative channels in the capturing and recombination processes. This result was confirm by decay time measurements. PL mapping of 2 inch ZnO epilayer shows high lateral homogeneity from PL intensity distribution and PL FWHM distribution. Hall-effect measurements and Electrochemical profiling (ECV) were used to characterize the electrical properties of ZnO samples. Hall-effect measurements indicated n-type behavior with carrier concentration of 2.0x1016 cm-3 and mobility of approximately 96 cm2/Vs. ECV profile versus depth measured for the top 2.5 μm thick sample gives surface carrier concentration is 2.0x1016 cm-3 increasing to a maximum value of 1.0x1018 cm-3 the semiconductor/substrate interface. P-n heterojuntions and mesa structures comprising MBE n-ZnO layers and CVD p-4H-SiC laser were manufactured and investigated. Electrical properties of the mesa diodes have been studied with Hall measurements, and current-voltage measurements (I-V). I-V measurements of the device show good rectifying behavior, from which a turn-on voltage of about 2 V was obtained. With the excitation of O and N gas mixture in a single plasma cell, followed by the sample annealing procedure. P-type ZnO:N layers with a net hole concentration 3x1017 cm-3 using was measured. The combination of low growth temperature, slightly O-rich conditions and post-growth annealing is shown to be effective way to obtain p-doping. Further efforts are necessary to improve structural quality of the low-temperature p-type ZnO:N films. Optical properties of ZnO based II-VI heterostructures and quantum structures have also been studied. The surface roughness of ZnxMg1−xO was as low as 0.7 nm. The optical band gap and photoluminescence peak can be turned to larger energy with the same high crystallinity and without significant change in the lattice constant. The prominent PL peaks related to the SQW show a systematic blueshift with decreasing well width, which is consistent with the quantum size effect. The SQW-related emission peaks exhibit an S-shaped (redshift-blueshiftredshift) behaviour with increasing temperature, which is in contrast with that ascribed to band gap shrinkage (redshift). The observed behavior is discussed in terms of localization at lateral interface potential fluctuations. For T >70 K the integrated PL intensity is thermally activated with activation energies much less than the band offsets. It is argued that the dominant mechanism leading to the quenching of the ZnO SQW-related PL is due to the thermionic emission of excitons out of the lateral potential minima caused by potential fluctuations, such as interface fluctuations by 1 ML. Stimulated emission has been achieved at room temperature in a separate confinement double heterostructure having a 3 nm wide SQW as an active region. It has been found that a critical parameter for the lasing is the inhomogeneous broadening of both QW and barrier emission bands. MBE process for ZnO has been developed where high quality ZnO epilayers and heterostructures can be grown by molecular beam epitaxy on sapphire substrate. For nitrogen doping of ZnO, Oxygen and nitrogen were activated in the single plasma cell. No reproducible and reliable experimental results on the achievement of p-type conductivity achieved. Stimulated emission has been achieved at room temperature.

Download or read book Encyclopedia of Chemical Processing written by Sunggyu Lee and published by Taylor & Francis US. This book was released on 2006 with total page 682 pages. Available in PDF, EPUB and Kindle. Book excerpt: Collecting information of vital interest to chemical, polymer, mechanical, electrical, and civil engineers, as well as chemists and chemical researchers, this "Encyclopedia "supplies nearly 350 articles on current design, engineering, science, and manufacturing practices-offering expertly written articles on technologies at the forefront of the field to maximize and enhance the research and production phases of current and emerging chemical manufacturing practices and techniques.

Download or read book Ultraviolet Electrically Injected Light Sources With Epitaxial ZnO Based Heterojunctions written by and published by . This book was released on 2007 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this effort, significant emphasis was placed on the epitaxial growth and in situ doping of ZnO for optoelectronic devices. The materials research efforts on ZnO have resulted in device-quality material on sapphire substrates for the desired laser diodes, where the eventual material quality improvements necessary for the devices are anticipated for future growth on ZnO substrates. P-type doping of ZnO was demonstrated using nitrogen, though the p-type behavior was found to be unstable over time. In situ arsenic and antimony doping of ZnO was demonstrated, exhibiting either weak p-type behavior or mixed p-type/n-type conduction, though with stable behavior over time. In addition to the binary ZnO, the growth of MgZnO and ZnO/MgZnO heterojunctions was studied. Quantum wells exhibiting efficient radiative recombination were demonstrated. and may form the basis of future ultraviolet LEDs and lasers. Device applications of the ZnO/MgZnO materials were studied, which included studies of ohmic contacts to ZnO, UV photoconductors, and thin film transistors. The integration of ferroelectric oxide thin films with ZnO was also investigated, as a potential means of locally inverting ZnO to p-type, and to achieve novel multi-functional devices for reconfigurable systems.

Download or read book Growth and Optoelectronic Properties of Al doped ZnO Nanowire written by 張竣榮 and published by . This book was released on 2012 with total page 74 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Flux Growth of ZnO Microcrystals and Growth of Doped Homoepitaxial ZnO Films by Liquid Phase Epitaxy written by and published by . This book was released on with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Zinc oxide is known as an outstanding material with desirable properties and a wide application range in optoelectronics, transparent electronics, etc. An increasingly important aspect is the fabrication of materials like ZnO by technologies which not only guarantee reproducibly high quality, but also facilitate one-step fabrication of the functional materials with a minimum effort in producing them by so-called green technologies. Moreover, mechanically untouched ZnO surfaces are desirable to exclude radiative losses due to a damaged surface layer. As the doping of hydrothermal grown bulk ZnO appears rather difficult and time consuming, LPE was employed to obtain high-quality single crystal films of several micrometer thickness. With the LPE growth technique the damaged surface layer is neutralized, at the same time doping can be realized and the sample surface is mechanically untouched. LPE is an advancement of the flux growth. Before growing films by LPE several flux experiments were done. Homoepitaxial ZnO films and microcrystals were grown from a LiCl solution at 640°C under ambient air conditions. ZnO is produced by a reaction of ZnCl2 with K2CO3, such way providing the feeding for continous growth. Doping and formation of solid solutions with ions such like Bi, Sb, Mo, and In was enabled through employment of the relevant pure metal, metal halogenide or metal oxide. The crystal quality has been investigated by SEM, EDX, XRD, DIC and PL.