S.K. Mohd Bakhori

Optical Analysis of Nanocrystalline ZnO Films Coated on Porous Silicon by Radio Frequency (RF) Magnetron Sputtering

Zinc oxide thin films have been deposited onto porous silicon (PSi) substrates at high growth rates by radio frequency (RF) sputtering using a ZnO target. The advantages of the porous Si template are economical and it provides a rigid structural material. Porous silicon is applied as an intermediate layer between silicon and ZnO films and it contributed a large area composed of an array of voids. The nanoporous silicon samples were adapted by photo electrochemical (PEC) etching technique on n-type silicon wafer with (111) and (100) orientation. Micro-Raman and photoluminescence (PL) spectroscopy are powerful and non-destructive optical tools to study vibrational and optical properties of ZnO nanostructures. Both the Raman and PL measurements were also operated at room temperature. Micro-Raman results showed that the A1(LO) of hexagonal ZnO/Si(111) and ZnO/Si(100) have been observed at around 522 and 530 cm–1, re- spectively. PL spectra peaks are distinctly apparent at 366 and 368 cm–1 for ZnO film grown on porous Si(111) and Si(100) substrates, respectively. The peak luminescence energy in nanocrystalline ZnO on porous silicon is blue-shifted with regard to that in bulk ZnO (381 nm). The Raman and PL spectra pointed to oxygen vacancies or Zn interstitials which are responsible for the green emission in the nanocrystalline ZnO.

Surface phonon polariton characteristics of In 0.04 Al 0.06 Ga 0.90 N/AlN/Al 2 O 3 heterostructure

Surface phonon polariton (SPP) characteristics of In(0.04)Al(0.06)Ga(0.90)N/AlN/Al(2)O(3) heterostructure are investigated by means of p-polarized infrared (IR) attenuated total reflection spectroscopy. Two absorption dips corresponding to In(0.04)Al(0.06)Ga(0.90)N SPP modes are observed. In addition, two prominent dips and one relatively weak and broad dip corresponding to the Al(2)O(3) SPP mode, In(0.04)Al(0.06)Ga(0.90)N/Al(2)O(3) interface mode, and Al(2)O(3) bulk polariton mode, respectively, are clearly seen. No surface mode feature originating from the AlN layer is observed because it is too thin. Overall, the observations are in good agreement with the theoretical predictions.

Catalyst‐free growth and characterization of ZnO nanoscrewdrivers prepared by thermal evaporation

Purpose – The purpose of this paper is to propose a simple physical evaporation route in which catalyst‐free zinc oxide (ZnO) nanoscrewdrivers were deposited on silicon (Si) (111) substrates.Design/methodology/approach – Prior to the deposition, the Si (111) wafer was cut into pieces of 2×2 cm2. Then, the wafers were dipped for 1 min into mixture buffered oxide etchant to remove native oxide. Then, the samples were rinsed in an ultrasonic bath cleaned with boiling acetone, ethanol, and de‐ionized (DI) water for 10 min. Lastly, the wafers were rinsed in 25 ml DI water in stirred and then were blown dry with nitrogen. In this technique, the starting material is high‐purity metallic zinc (Zn) powder (99.99 per cent pure). Following, the Zn films were then annealed under air environment in the furnace at 500°C for 1 h deprived of any catalysts.Findings – These ZnO samples were studied by scanning electron microscopy, high‐resolution X‐ray diffraction (HR‐XRD), and photoluminescence (PL) spectroscopy. Atomic f...

Nanocrystalline ZnO Film Grown on Porous SnO2/Si(111) Substrate

Porous tin oxide was prepared on silicon(111) substrate by the sol–gel route. Then, the samples were dried in air at 600°C for 30 min in an electric furnace. Scanning electron microscope (SEM) images indicated the high density of the pores. Circular microvoids formed by the rigid shaped microarray network of 200–300 nm sizes are clearly seen in the plan view SEM image. The high homogeneity and uniformity of the porous region could also be visualized by this easy method. Nanocrystalline zinc oxide (ZnO) thin films have been deposited onto porous SnO2substrates at high growth rates by radio frequency (RF) sputtering using a ZnO target. The surface morphology of the nanocrystalline ZnO films was characterized by scanning electron microscope (SEM). Photoluminescence (PL) spectroscopy is a powerful, contactless and excellent nondestructive optical tool to study the acceptor binding energy of ZnO nanostructures. The PL measurements were also operated at room temperature. The peak luminescence energy in nanocrystalline ZnO on porous SnO2 is blue-shifted with regard to that in bulk ZnO (381 nm). PL spectra peaks are distinctly apparent at 375 nm for ZnO film grown on porous SnO2/Si(111) substrates.

Nanoporous ZnO prepared by electrochemical anodization deposition

Anodic physical deposition is a method that joins technical simplicity, environment friendly, non-toxic, low investment cost, and ease in morphology control. Nanoporous ZnO with high internal rough surface and polycrystalline nature has been prepared via a simple chemical technique. Anodization of Znic (Zn) foil was studied in a mixed of ammonium sulfate and sodium hydroxide solution under the affect of various anodization durations. The as-prepared samples were studied by X-ray diffraction (XRD), and energy dispersive analysis of X-rays (EDX). An optical characterization by a Raman spectrometer was performed to investigate their optical properties. The PL and Raman results revealed both good compromise with the features of our samples and dormant for forthcoming utilizations for example smart sensors system and other modern solid state technologies. The formation of porous structures has been confirmed by Raman spectroscopy and scanning electron microscopy investigations.

Photoluminescence and XRD Crystalline Studies of InxAlyGa1-X-Yn Quaternary Alloys

Recently, InxAlyGa1−x−yN quaternary alloys have attracted much research interest because of the great flexibility in tailoring their band gap profile while maintaining their lattice-matching and structural integrity. In this paper, we present the study of crystalline quality of InxAlyGa1−x−yN quaternary alloys by using photoluminescence (PL) spectroscopy and X-ray diffraction (XRD) technique. The InxAlyGa1−x−yN quaternary alloys were grown on sapphire by molecular beam epitaxy with indium (In) mole fraction, x, ranging from 0 to 0.1 and constant aluminium (Al) mole fraction (y = 0.06). Through this study, the variation of crystalline quality of the InAlGaN epilayers as a function of In composition is investigated by analyzing the full width at half maximum (FWHM) of the PL peak and (0002) InxAlyGa1−x−yN diffraction peaks. The results revealed that the FWHM of the PL and the (0002) InxAlyGa1−x−yN diffraction peaks gradually increased as the In composition is increased indicating the decreased of the samples quality. The broadening may probably be attributed to the point defects leading to non-uniformity of the quaternary layers.

Structural and optical properties of Alx Iny Ga1−x−y N quaternary alloys grown on sapphire substrates by molecular beam epitaxy

Purpose – The purpose of this paper is to study the structural and optical characterization of Alx Iny Ga1−x−y N quaternary epilayers, which were grown on c‐plane (0001) sapphire substrates with AlN as buffer layers using plasma assisted molecular beam epitaxy technique with indium (In) mole fraction y ranging from 0.0 to 0.1 and constant aluminum (Al) mole fraction x=0.06.Design/methodology/approach – High‐resolution X‐ray diffraction rocking curve (HRXRD‐RC), scanning electron microscopy (SEM), energy dispersive X‐ray spectrometry (EDX), and photoluminescence (PL) spectroscopy have been measured on quaternary Alx Iny Ga1−x−y N thin films at room temperature.Findings – HRXRD‐RC measurements confirmed that the Alx Iny Ga1−x−y N alloys had wurtzite structure. SEM images, element composition analysis by EDX, provided the evidence to show the existence of defects inside the samples contaminated by silicon from previous growth leading to nonuniformity of the epilayers, which caused decreased in the quality of...

Electrochemical Self-Assembly of ZnO Nanosheetlike Structures

ZnO nanosheetlike structures were synthesized on zinc (Zn) foil substrates by electrochemical deposition method in ZnCl2 aqueous solutions at a temperature of 90 °C. In addition, the synthetic parameters in this work allow additional structural direction for ZnO nanoscaled structures. The morphology growth from smooth plane structures to nanosheet like structures could be accomplished by modifying the current densities of electrodeposition. In the photoluminescence (PL) spectra of the as-synthesized ZnO samples, typically there are few oxygen vacancies or interstitial Zn centers would be produced when the electrochemical deposition was performed out with a low current density. The UV peak is usually considered as the characteristic emission of ZnO nanosheetlike structures and attributed to the band edge emission or the exciton transition. All XRD diffraction peaks of ZnO nanosheetlike structures are shown in a good agreement with hexagonal structure. The average particle size was calculated using the Debye-Scherrer formula. ZnO nanosheetlike structures processed for various current densities have different size.

n-ZnO/p-Si heterojunctions for photosensor applications

Photodetectors functioning in the short wavelength (from 300nm to 500 nm) ultraviolet part are paramount devices that can be applied in civil and military applications. In this work, we have demonstrated the n-ZnO/p-Si heterojunction photodiodes. A zinc (Zn) metal was coated on silicon (Si) substrate from high purity Zn metal targets by dc sputtering deposition technology. Subsequent, the Zn thin films were then annealed in the conventional furnace annealing temperatures under flowing oxygen gas environment. As a result of current-voltage (I–V) measurements, the data analysis of I–V characteristics of the device exhibited the ordinary excellent rectifying behavior for the heterojunctions. The UV photocurrent versus reverse-bias voltage measurement was done using an LTV lamp. Under a dark condition, the n-ZnO/p-Si diodes exhibit intense rectifying behavior characterized by the I–V measurement. For a reverse bias, high photocurrent is acquired when the crystalline grade of n-type ZnO film is good sufficient to transmit the illuminated into p-Si.

Photoluminescence Characterization of ZnO Thin Films Grown by RF‐ Sputtering

This article presents photoluminescence (PL) characterization of ZnO thin films deposited by radio‐frequency magnetron sputtering method on sapphire and n‐type Si (100) substrates. PL measurements were carried out at room temperature to investigate the energy band gaps and optical quality of the ZnO thin films. In order to draw a specific picture of surface morphology of ZnO thin films, atomic force microscope images were taken. All the results were compared to the results obtained from the bulk ZnO sample. The results revealed that the energy band gap of ZnO thin films grown on n‐type Si (100) is higher than ZnO on sapphire. However, energy band gap of bulk ZnO is higher compared to both ZnO on n‐type Si (100) and sapphire (Al2O3). This is probably due to the crystalline quality because good crystallinity increases the radiation recombination and hence increase the intensity of the NBE emission.