https://chemistry.beloit.edu/classes/nanotech/ZnO/mattoday10_05_40.pdf

ZnO - nanostructures, defects, and devices

Few-layered films of WS2, synthesized by chemical vapor deposition on quartz, are successfully used as light sensors. The film samples are structurally characterized by Raman spectroscopy, atomic force microscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The produced samples consist of few layered sheets possessing up to 10 layers. UV–visible absorbance spectra reveals absorption peaks at energies of 1.95 and 2.33 eV, consistent with the A and B excitons characteristic of WS2. Current–voltage (I–V) and photoresponse measurements carried out at room temperature are performed by connecting the WS2 layered material with Au/Ti contacts. The photocurrent measurements are carried out using five different laser lines ranging between 457 and 647 nm. The results indicate that the electrical response strongly depends on the photon energy from the excitation lasers. In addition, it is found that the photocurrent varies non-linearly with the incident power, and the generated photocurrent in the WS2 samples varies as a squared root of the incident power. The excellent response of few-layered WS2 to detect different photon wavelengths, over a wide range of intensities, makes it a strong candidate for constructing novel optoelectronic devices.

Photosensor Device Based on Few-Layered WS2 Films

One-dimensional (1D) metal-oxide nanostructures are ideal systems for exploring a large number of novel phenomena at the nanoscale and investigating size and dimensionality dependence of nanostructure properties for potential applications. The construction and integration of photodetectors or optical switches based on such nanostructures with tailored geometries have rapidly advanced in recent years. Active 1D nanostructure photodetector elements can be configured either as resistors whose conductions are altered by a charge-transfer process or as field-effect transistors (FET) whose properties can be controlled by applying appropriate potentials onto the gates. Functionalizing the structure surfaces offers another avenue for expanding the sensor capabilities. This article provides a comprehensive review on the state-of-the-art research activities in the photodetector field. It mainly focuses on the metal oxide 1D nanostructures such as ZnO, SnO2, Cu2O, Ga2O3, Fe2O3, In2O3, CdO, CeO2, and their photoresponses. The review begins with a survey of quasi 1D metal-oxide semiconductor nanostructures and the photodetector principle, then shows the recent progresses on several kinds of important metal-oxide nanostructures and their photoresponses and briefly presents some additional prospective metal-oxide 1D nanomaterials. Finally, the review is concluded with some perspectives and outlook on the future developments in this area.

https://www.mdpi.com/1424-8220/9/8/6504/pdf

A Comprehensive Review of One-Dimensional Metal-Oxide Nanostructure Photodetectors

One-dimensional (1D) metal-oxide nanostructures are ideal systems for exploring a large number of novel phenomena at the nanoscale and investigating size and dimensionality dependence of nanostructure properties for potential applications The construction and integration of photodetectors or optical switches based on such nanostructures with tailored geometries have rapidly advanced in recent years Active 1D nanostructure photodetector elements can be configured either as resistors whose conductions are altered by a charge-transfer process or as field-effect transistors (FET) whose properties can be controlled by applying appropriate potentials onto the gates Functionalizing the structure surfaces offers another avenue for expanding the sensor capabilities This article provides a comprehensive review on the state-of-the-art research activities in the photodetector field It mainly focuses on the metal oxide 1D nanostructures such as ZnO, SnO(2), Cu(2)O, Ga(2)O(3), Fe(2)O(3), In(2)O(3), CdO, CeO(2), and their photoresponses The review begins with a survey of quasi 1D metal-oxide semiconductor nanostructures and the photodetector principle, then shows the recent progresses on several kinds of important metal-oxide nanostructures and their photoresponses and briefly presents some additional prospective metal-oxide 1D nanomaterials Finally, the review is concluded with some perspectives and outlook on the future developments in this area

A comprehensive review of one-dimensional metal-oxide nanostructure photodetectors

Effects of annealing on properties of ZnO thin films prepared by electrochemical deposition in chloride medium

ZnO nanorod arrays fabricated on ZnO buffer layers on Si wafers were grown using a low-temperature solution method and were characterized by various techniques. Buffer layers were prepared using metal organic chemical vapor deposition and a sputter-oxidation method. Aligned ZnO nanorods were deposited at 90°C on the substrates by a hydrothermal treatment using a zinc salt and aqueous ammonia solution. The ZnO nanorod arrays were characterized by scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, Raman spectroscopy, and photoluminescence spectroscopy. The as-grown ZnO nanorod arrays exhibited broad deep-level emission centered at ∼564nm. The intensity of the deep-level emission decreased and band edge emission centered at 379nm appeared after air annealing. Samples annealed in hydrogen showed only band edge emission.

Characterization of ZnO nanorod arrays fabricated on Si wafers using a low-temperature synthesis method

A high-density vertically well-aligned ZnO nanoneedle array was fabricated on a ZnO-buffer film on silicon substrates by metal-organic chemical vapor deposition at a growth temperature of 480–500°C. Highly crystalline ZnO nanoneedle arrays showed a strong near-bandedge emission at 380nm in room-temperature photoluminescence. A simple ultraviolet (UV) sensor was fabricated by evaporating a Ag electrode on the ZnO nanoneedle array. The photoresponse results showed very high photocurrent (∼10−4A) from ZnO nanoneedles compared to a single-nanowire sensor (∼10−8A), indicating high sensitivity of the photosensor. It also showed fast rise and decay times in UV-on/off switching measurements.

Photoconductivity of vertically aligned ZnO nanoneedle array

Evolution of morphology change was investigated for ZnO nanoneedle array grown by low-temperature MOCVD. Well-aligned ZnO nanoneedle array was deposited on the ZnO buffer-film/Si substrate at temperatures below 500°C. A rod-shaped ZnO nanowire in the initial growth stage changed into needle-shaped as the deposition proceeds. ZnO nanoneedle array deposited on the annealed buffer-film showed better alignment compared to that deposited on the as-grown film. XPS analysis showed that Zn 2p peak has a single binding energy state of a stoichiometric Zn–O bond while O 1 s peak has three different chemical binding states. Highly crystalline ZnO nanoneedle array showed a strong bandedge emission at 380 nm in photoluminescence measurements.

LOW-TEMPERATURE SYNTHESIZED ZnO NANONEEDLES: XPS AND PL ANALYSIS

High density and vertically well-aligned ZnO nanoneedle arrays were fabricated on the ZnO thin film deposited on silicon substrates. The ZnO buffer layer and nanoneedles were synthesized by metal organic chemical vapor deposition using diethylzinc and oxygen gas. The ZnO buffer film was grown at 250 degrees C and the growth temperature of nanoneedles was in the range of 480-500 degrees C. As-grown ZnO nanoneedles showed single crystalline structure of ZnO (002). The crystalline properties of three samples (A: as-deposited ZnO buffer layer, B: annealed buffer film, C: ZnO nanoneedles) were compared using XRD and Raman spectroscopy. The synthesized ZnO nanoneedles (sample C) showed highest crystalline quality among three samples. The field emission properties of ZnO nanoneedles were investigated, which showed low turn on field of 4.8 Vmicrom(-1) and high field enhancement factor of 3.2 x 103.

Dongseok Park

Papers

Characterization of ZnO nanorod arrays fabricated on Si wafers using a low-temperature synthesis method

Photoconductivity of vertically aligned ZnO nanoneedle array

LOW-TEMPERATURE SYNTHESIZED ZnO NANONEEDLES: XPS AND PL ANALYSIS

Fabrication and characterization of ZnO nanoneedle array using metal organic chemical vapor deposition.