Au/n-ZnO rectifying contact fabricated with hydrogen peroxide pretreatment

Au contacts were deposited on n -type ZnO single crystals with and without hydrogen peroxide pretreatment for the ZnO substrate. The Au/ZnO contacts fabricated on substrates without H2 O2 pretreatment were Ohmic and those with H2 O2 pretreatment were rectifying. With an aim of fabricating a good quality Schottky contact, the rectifying property of the Au/ZnO contact was systemically investigated by varying the treatment temperature and duration. The best performing Schottky contact was found to have an ideality factor of 1.15 and a leakage current of ∼ 10-7 A cm-2. A multispectroscopic study, including scanning electron microscopy, positron annihilation spectroscopy, deep level transient spectroscopy, x-ray photoelectron spectroscopy, and photoluminescence, showed that the H2 O2 treatment removed the OH impurity and created Zn-vacancy related defects hence decreasing the conductivity of the ZnO surface layer, a condition favorable for forming good Schottky contact. However, the H2 O2 treatment also resulted in a deterioration of the surface morphology, leading to an increase in the Schottky contact ideality factor and leakage current in the case of nonoptimal treatment time and temperature. © 2008 American Institute of Physics.published_or_final_versio

Nitrogen doped-ZnO/n-GaN heterojunctions

Nitrogen-doped ZnO nanorods were prepared by electrodeposition using two different Zn precursors (zinc nitrate and zinc acetate), while all other growth conditions (dopant precursor, concentration, growth temperature, and bias) were identical. We have shown that the precursor used affects the properties of the ZnO nanorods, and that the presence of rectifying properties in n-GaN/N:ZnO heterojunctions is strongly related to the use of nitrate precursor for ZnO growth. The difference in the properties of ZnO obtained from two precursors is attributed to the differences in native defect and impurity concentrations, which could affect the electronic properties of the samples. © 2011 American Institute of Physics.published_or_final_versio

Hydrogen peroxide treatment induced rectifying behavior of Aun-ZnO contact

Conversion of the Aun-ZnO contact from Ohmic to rectifying with H2 O2 pretreatment was studied systematically using I-V measurements, x-ray photoemission spectroscopy, positron annihilation spectroscopy, and deep level transient spectroscopy. H2 O2 treatment did not affect the carbon surface contamination or the EC -0.31 eV deep level, but it resulted in a significant decrease of the surface OH contamination and the formation of vacancy-type defects (Zn vacancy or vacancy cluster) close to the surface. The formation of a rectifying contact can be attributed to the reduced conductivity of the surface region due to the removal of OH and the formation of vacancy-type defects. © 2007 American Institute of Physics.published_or_final_versio

Solution-based growth of ZnO nanorods for light-emitting devices: Hydrothermal vs. electrodeposition

ZnO nanorods have been grown by two inexpensive, solution-based, low-temperature methods: hydrothermal growth and electrodeposition. Heterojunction n-ZnO nanorods/p-GaN light-emitting diodes have been studied for different nanorod growth methods and different preparation of the seed layer. We demonstrate that both the nanorod properties and the device performance are strongly dependent on the growth method and seed layer. All the devices exhibit light emission under both forward and reverse bias, and the emission spectra can be tuned by ZnO nanorod deposition conditions. Electrodeposition of rods or a seed layer results in yellow emission, while conventional hydrothermal growth results in violet emission. © The Author(s) 2010. This article is published with open access at Springerlink.com.published_or_final_versionSpringer Open Choice, 01 Dec 201

Nitrogen doped-ZnO/n-GaN heterojunctions

Author name used in this publication: Aleksandra B. DjurišičAuthor name used in this publication: Kok Wai CheahAuthor name used in this publication: Chi Chung LingAuthor name used in this publication: Wai Kin ChanAuthor name used in this publication: Patrick W. K. FongAuthor name used in this publication: Hsian Fei Lui2011-2012 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Hydrothermal treatment of ZnO nanostructures

Hydrothermal treatment of ZnO nanostructures involves low temperatures (150-200 °C) and elevated water vapor pressure for the purpose of the improvement in the material properties. Under such moderate conditions, no significant changes in the morphology would be expected. Nevertheless, such treatment results in a significant change of nanostructured morphologies of ZnO. The observed changes are dependent on the starting material properties and the substrate used for the growth. In the case of Si substrate, hydrothermal treatment results in significant Si contamination of the samples. In terms of the optical properties, improvements are observed only in some cases, while samples with excellent starting optical properties are degraded by the treatment. Mechanisms responsible for the observed changes are discussed. © 2011 Elsevier B.V. All rights reserved.link_to_subscribed_fulltex

Influence of hydrothermal treatment on morphology and properties of ZnO nanostructures

Hydrothermal treatment at low temperature (∼150°C) was performed on different ZnO nanostructures grown on different substrates such as Si and ITO/glass. The water vapor environment and the high pressure of water vapor at that temperature were expected to improve the optical properties of ZnO nanorods. Under such mild condition, no significant morphology changes are expected. However, significant changes were observed in both morphology and optical properties. The morphology of ZnO nanostructures has been changed in various ways, depending on the growth conditions of ZnO nanostructures as well as the substrates. In the terms of optical properties, the increase of photoluminescence (PL) intensity was observed and the UV to visible ratio of ZnO PL spectra was also improved in some cases, while in others there has been no improvement. Hydrothermal treatment was also performed on zinc oxide precursor on Si substrates to study the possible Si contamination during the procedure. Zinc nitrate solution in ethanol was used as the precursor. As a result, an increase of the intensity of the broad peak around 430 nm which is related to silicon oxide was obtained. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).link_to_subscribed_fulltex

Solution-based growth of ZnO nanorods for light-emitting devices : hydrothermal vs. electrodeposition

2010-2011 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Undoped p-type ZnO nanorods synthesized by a hydrothermal method

Zinc oxide is a very promising material for short-wavelength light-emitting devices due to its large band gap and high exciton binding energy. Although great progress has been made in recent years, p-type doping and control over native defects introduced during or after material growth are still significant problems that hinder the development of efficient ZnO based optoelectronic devices. Here we demonstrate a versatile method for the growth or p-type or n-type ZnO nanorods from the same growth solution at temperature as low as 90 °C, where the conductivity type is controlled by the preparation of the seed layer for nanorod growth. The differences in the conductivity type can be attributed to dependency of native defect concentrations and hydrogen incorporation on the seed layer preparation method. Room temperature electroluminescence has been demonstrated from homojunction and heterojunction light emitting diodes containing p-ZnO nanorods. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA,.link_to_subscribed_fulltex