Room temperature electroluminescence from the n-ZnO/p-GaN heterojunction device grown by MOCVD

The heterojunction light-emitting diode with n-ZnO/p-GaN structure was grown on (0 0 0 1) sapphire substrate by metalorganic chemical vapor deposition (MOCVD) technique. The heterojunction structure was consisted of an Mg-doped p-type GaN layer with a hole concentration of ∼10¹⁷ cm⁻³ and a unintentionally doped n-type ZnO layer with an electron concentration of ∼10¹⁸ cm⁻³. A distinct blue-violet electroluminescence with a dominant emission peak centered at ∼415 nm was observed at room temperature from the heterojunction structure under forward bias conditions. The origins of the electroluminescence (EL) emissions are discussed in comparison with the photoluminescence spectra, and it was supposed to be attributed to a radiative recombination in both n-ZnO and p-GaN sides.     

Fabrication of p-type ZnO nanowires based heterojunction diode

Vertically aligned p-type ZnO (Li–N co-doped) nanowires have been synthesized by hydrothermal method on n-type Si substrate. X-ray diffraction pattern indicated a strong peak from (0 0 0 2) planes of ZnO. The appearance of a strong peak at 437 cm⁻¹ in Raman spectra was attributed to E₂ mode of ZnO. Fourier transformed infrared studies indicated the presence of a distinct characteristic absorption peaks at 490 cm⁻¹ for ZnO stretching mode. Compositional studies revealed the formation of Li–N co-doped ZnO, where Li was bonded with both O and N. The junction properties of p-type ZnO nanowires/n-Si heterojunction diodes were evaluated by measuring I–V and C–V characteristics. I–V characteristics exhibited the rectifying behavior of a typical p–n junction diode.     

MBE n-ZnO/MOCVD p-GaN heterojunction light-emitting diode

The growth, fabrication, and subsequent electroluminescence (EL) characterization of an n-ZnO/p-GaN heterojunction light-emitting diode prepared on c-Al₂O₃ substrate are presented. The diode-like I-V characteristics and room temperature EL spectrum with an intense broadband emission in the yellow-green spectral region has been observed with forward bias applied. Photoluminescence (PL) and Raman spectra of the n-ZnO and p-GaN films were also measured. By comparing PL and EL spectra, it was concluded that the deep-level defect-related emission mainly originated from the GaN epitaxial layer.     

Repeated temperature modulation epitaxy for p-type doping and light-emitting diode based on ZnO.

Since the successful demonstration of a blue light-emitting diode (LED), potential materials for making short-wavelength LEDs and diode lasers have been attracting increasing interest as the demands for display, illumination and information storage grow. Zinc oxide has substantial advantages including large exciton binding energy, as demonstrated by efficient excitonic lasing on optical excitation. Several groups have postulated the use of p-type ZnO doped with nitrogen, arsenic or phosphorus, and even p-n junctions. However, the choice of dopant and growth technique remains controversial and the reliability of p-type ZnO is still under debate. If ZnO is ever to produce long-lasting and robust devices, the quality of epitaxial layers has to be improved as has been the protocol in other compound semiconductors. Here we report high-quality undoped films with electron mobility exceeding that in the bulk. We have used a new technique to fabricate p-type ZnO reproducibly. Violet electroluminescence from homostructural p-i-n junctions is demonstrated at room-temperature.     

Ultraviolet electroluminescence from ZnO/polymer heterojunction light-emitting diodes

We report ultraviolet electroluminescence at 390 nm from diode structures consisting of electrodeposited ZnO nanorods sandwiched between a transparent SnO(2) film and a p-type conducting polymer. The nanorods are embedded in an insulating polystyrene layer. ZnO deposition occurs at 90 degrees C and produces vertically oriented nanorods with very high uniformity over areas of approximately 20 cm(2). Electron diffraction shows the nanorods to be single crystalline wurtzite ZnO. As-grown films show a broad electroluminescence band over the visible spectrum. Annealing at moderate temperatures (T = 300 degrees C) increases the emission and strongly raises the excitonic contribution. Optimally processed films show a narrow ultraviolet electroluminescence line at approximately 390 nm.     

Formation of novel homojunction device using p-type ZnO:Co shell coating on n-type ZnO nanowires

P-type ZnO:Co thin film was spin coated onto n-type ZnO nanowire arrays to form a novel ZnO homojunction device using a fully solution-based process. The optoelectronic and structural properties of the homojunction device were extensively characterized by using scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy and photoluminescence emission measurement and current voltage measurement. It was found that the applied ZnO:Co coating bundles the nanowires together and suppress surface defects on the nanowire. Dark and illuminated device confirms the pn junction formation and its light sensitivity properties.     

Sputter deposited ZnO nanowires/thin film structures on glass substrate

Integrated ZnO nanowires/thin film structures were grown using radio-frequency magnetron sputter deposition on amorphous glass substrates having an electroless plated copper surface layer. The growth took place under different deposition times and O₂/Ar ratios. The substrate was not heated or biased during the deposition. Regardless of the O₂/Ar ratio, both nanowires and the film grew simultaneously. However, the growth of the nanowires and the film was diffusion-controlled and reaction-controlled, respectively. On the other hand, the O₂/Ar ratio substantially affected the crystal structure and morphology of the resulting ZnO deposits.     

Preparation and application in p-n homojunction diode of p-type transparent conducting Ga-doped SnO2 thin films

The direct preparation of p-type transparent conducting Ga-doped SnO₂ thin films and their fundamental application in transparent p-n homojunction diode were realized. The films were grown in an active oxygen ambient using reactive rf magnetron sputtering without post-deposition annealing involved. This method improved the electrical properties of the films while maintaining their optical transparency. By growing a p-type thin film on commercial n-type SnO₂:F-coated glass, transparent p-n homojunction diode was obtained. It exhibits a distinct current-voltage rectifying characteristic, manifesting this p-type thin film and the fabrication technology are suitable for industrial applications.     

The recent advances of research on p-type ZnO thin film

ZnO is a direct wide-band gap (3.37 eV) compound semiconductor with large exciton binding energy (60 meV) at room temperature. Therefore it has a strong potential for various short-wavelength optoelectronic device, and now attracts tremendous renew interests for developing highly efficient ZnO-based optoelectronic devices. While high quality ZnO p–n junction materials obtained is the key step of its optoelectronic application. Whereas ZnO thin film is naturally only n-type conductivity due to a large number of native defects, such as oxygen vacancies and zinc interstitials, which lead to difficulty in achieving p-type ZnO thin film. Therefore the fabrication of p-type ZnO thin film has been a key and hotspot of the research on ZnO. This article summarizes the recent advances of the studies on p-type ZnO thin film and the correlative several important breakthroughs in ZnO homo-junction devices based on succeeding on fabrication of p-type ZnO film. Although the achievement obtained as summarized, there is also a long way from the real application of ZnO-based optoelectronic device. We here also discuss the problem and relevant possible solution for the fabrication of p-type ZnO film and its optoelectronic application. And forecast the preparation trends of p-type ZnO thin film.     

Fabrication of ZnO thin film diode using laser annealing

A p-n homojunction was obtained by Nd:YAG laser annealing of Zn₃P₂/n-ZnO thin film. The deposition process of ZnO and Zn₃P₂ thin film was performed by pulsed laser deposition (PLD). A p-n junction was formed by Nd:YAG laser annealing of Zn₃P₂/n-ZnO thin film and showed typical I-V characteristics of a diode. Laser annealing could be a useful technique for the fabrication of an ultraviolet light-emitting diode or an ultraviolet laser diode.     

Room temperature interactions in Ni/metal thin film couples

Interactions in Ni/metal thin film couples at room temperature were studied. It was found that nickel reacts with gallium, indium and tin to form NiGa₄, Ni₂In₃, Ni₁₀In₂₇ and NiSn, but no reaction was observed with bismuth, cadmium, germanium, magnesium, manganese, antimony, samarium and zinc under the conditions employed.     

Room temperature magneto-optics of nanostructured ZnO:Mn thin film grown by spray pyrolysis

Undoped ZnO and ZnO:Mn thin films with different amounts of Mn concentration (5, 10 and 15 mol%) were grown on glass substrates by spray pyrolysis technique. X-ray diffraction patterns showed that the undoped ZnO thin film exhibited wurtzite structure preferably oriented in c-axis direction and the doped samples were polycrystalline. The surface morphology and topography of the films were investigated by SEM and STM micrographs. Magneto-optical characterizations of the samples were carried out by using Kerr and Faraday effects spectroscopy. Kerr effect studies showed that all Mn doped thin films exhibited the room temperature ferromagnetism. The magnetic ordering observed in the film with 5 mol% Mn concentration was stronger comparing to the other doped samples. The carrier densities of the samples were calculated by using a method based on the Faraday rotation. A clear relation between sp-d coupling and strength of magnetic ordering with carrier density was observed.     

Room temperature interactions in Ag-metals thin film couples

The results of room temperature interactions of silver and various metals in thin films are presented. It has been found that aluminium, gold, bismuth, chromium, copper, antimony and samarium do not react with silver under the conditions given, but cadmium, gallium, indium, tin, tellurium and zinc do, and the reactions lead to the formation of corresponding intermetallic compounds. In the AgGa system only one compound is formed, which has been identified as Ag₃Ga. In the AgIn system, with less than 50 wt.% In, one compound is formed and this has been identified as Ag₂In. A compound formed with over 50 wt.% In has been identified as AgIn₂ LT (low temperature phase). Between 60 and 120°C this compound transforms into AgIn₂ MT (medium temperature phase). In the AgSn system the compound Ag₃Sn is formed and in the AgTe system the compounds Ag₂Te and Ag₅Te₃ are formed.     

Enhanced acetone detection using Au doped ZnO thin film sensor

Zinc oxide (ZnO) thin films are prepared using sol–gel method for acetone vapor sensing. Zinc acetate dihydrate (Zn(CH₃COO)₂·2H₂O) was taken as starting material and a stable and homogeneous solution was prepared in ethanol by deliquescing the zinc acetate and distinct amount of monoethanolamine as a stabilizing agent. The prepared solution was then coated on silicon substrates by spin coating method and then annealed at 650 °C for preparing ZnO thin films. The thickness of the film was maintained at 410 nm. The structural, morphological and optical studies were done for the synthesized ZnO thin films. The operating temperature and sensor response is considered to be an important parameter for the gas sensing behavior of any material. Therefore, the present study examined the effect of sensing behavior of 3% v/v gold (Au) doped ZnO thin films as a sensor. The response characteristics of 410 nm ZnO thin film for temperature ranging from 180 to 360 °C were determined for the acetone vapors. The reported study provides a significant development towards acetone sensors, where a very high sensitivity with rapid response and recovery times are reported with lowered optimal operating temperature as compared to bare ZnO nano-chains like structured thin films. In comparison to the bare ZnO thin films giving a response of 63 at an operating temperature of 320 °C, a much better response of 132.3 was observed for the Au doped ZnO thin films at an optimised operating temperature of 280 °C for a concentration of 500 ppm of acetone vapors.     

Conductive Ga doped ZnO/Cu/Ga doped ZnO thin films prepared by magnetron sputtering at room temperature for flexible electronics

Ga doped ZnO(GZO)/Cu/GZO multilayers were deposited by magnetron sputtering on polycarbonate substrates at room temperature. We investigated the structural, electrical, and optical properties of multilayers at various thicknesses of Cu and GZO layers. The lowest resistivity value of 3.3 × 10^− 5 Ω cm with a carrier concentration of 2.9 × 10²² cm^− 3 was obtained at the optimum Cu (10 nm) and GZO (10 nm) layer thickness. The highest value of figure of merit φ_TC is 2.68 × 10^− 3 Ω^− 1 for the GZO (10 nm)/Cu(10 nm)/GZO(10 nm) multilayer. The highest average near infrared reflectivity in the wavelength range 1000-2500 nm is as high as 70% for the GZO(10 nm)/Cu(10 nm)/GZO(10 nm) multilayer.     

Scale-up synthesis of ZnO nanorods for printing inexpensive ZnO/polymer white light-emitting diode

In this study, possibilities of scaling up the synthesis of zinc oxide (ZnO) nanorods (NRs) by the hydrothermal method have been explored. It was found that batches yielding several grams can easily be made using common and easily available materials. Further, a printable composition was fabricated by mixing the obtained ZnO NRs into a common solvent-based screen printable varnish. Scanning electron microscope, high-resolution transmission electron microscope, X-ray diffraction, UV–vis spectroscopy analysis of the scaled up batch indicated that the ZnO nanostructures were of NRs shape, well crystalline and having less defects. Using the ZnO NRs-based printable composition a device fabrication on a flexible substrate was demonstrated, producing a flexible light-emitting device being highly tolerant to bending.     

Mn、Co掺杂ZnO薄膜结构及发光特性研究

利用脉冲激光沉积(PLD)方法在Si(100)衬底上制备了ZnO、Zn0.8Mn0.2O、Zn0.8Co0.2O薄膜.薄膜的晶体结构和表面形貌采用X射线衍射仪和原子力显微镜测试.表明薄膜具有明显的c轴择优生长取向,薄膜表面较为平整,颗粒尺寸在纳米量级,薄膜中晶粒的生长模式为"柱状"模式.此外,Mn、Co掺入后,薄膜的X射线衍射峰有小角度偏移,这与 Mn2 、Co2 离子半径有关.PL谱显示Mn、Co掺杂ZnO薄膜的蓝、绿发光峰的位置相对纯的ZnO薄膜没有改变,还出现了紫外发光峰,其中Mn掺杂的蓝、绿光峰的强度减弱,Co掺杂的蓝光峰强度减弱,绿光峰强度增强.这是因为Mn、Co掺入改变了ZnO本征缺陷的浓度,发光峰的强度也随之而改变.     

The effect of hydrogen annealing on the molybdenum doped ZnO thin film

The electrical characteristics of hydrogen annealing on the molybdenum doped ZnO (MZO) thin film were discussed in the paper. The MZO film was deposited by an radio frequency sputtering, then it was annealed in hydrogen with a microwave plasma chemical vapor deposition system. The resistivity of MZO was decreased from 1.1 × 10^?2 to 9.5 × 10^?3 Ω cm after the hydrogen annealing. Improvements of the electrical properties are both due to the defects repairing through annealing and hydrogen doping effects of the MZO thin film. The higher temperature annealed MZO film shows slightly lower transmittance which is due to the higher carrier concentration.     

ZnO缓冲层上低温生长Al掺杂的ZnO薄膜

采用射频磁控溅射法在ZnO缓冲层上制备了不同Al掺杂量的ZnO（AZO）薄膜。利用X射线衍射（XRD）、扫描电子显微镜（SEM）和光致发光（PL）等表征技术,研究了AZO薄膜的微观结构、表面形貌和发光特性。结果表明,随着Al掺杂量的增加,ZnO薄膜的择优取向性发生了改变,且当Al的掺杂量为0.81%（原子分数）时,（002）衍射峰与其它衍射峰强度的比值达到最大,表明适合的Al掺杂使ZnO薄膜的择优取向性得到了改善。在可见光范围内薄膜的平均透过率超过70%。通过对样品光致发光（PL）谱的研究,发现所有样品出现了3个发光峰,分别对应于以444nm（2.80eV）、483nm（2.57eV）为中心的蓝光发光峰和以521nm（2.38eV）为中心较弱的绿光峰。并对样品的发光机理进行了详细的探讨。