Photoluminescence of ZnO Nanocrystals Embedded in BaF2 Matrices by Magnetron Sputtering

2008 ◽  
Vol 8 (3) ◽  
pp. 1160-1164
Author(s):  
C. H. Zang ◽  
Y. C. Liu ◽  
R. Mu ◽  
D. X. Zhao ◽  
J. Y. Zhang ◽  
...  
Keyword(s):  
Magnetron Sputtering ◽  
Raman Scattering ◽  
Free Exciton ◽  
Wide Band ◽  
Zno Films ◽  
Near Band Edge ◽  
Band Edge Emission ◽  
Ultraviolet Emission ◽  
Pl Spectra ◽  
Zno Nanocrystals

This paper describes ZnO nanocrystals embedded in BaF2 matrices by the magnetron sputtering method in an attempt to use fluoride as a shell layer to embed ZnO nanocrystals core. BaF2 is a wide-band gap material, and can confine carriers in the ZnO films. As a result, the exciton emission intensity should be enhanced. The sample was annealed at 773 K, and X-ray diffraction (XRD) results showed that ZnO nanocrystals with wurtzite structure were embedded in BaF2 matrices. Raman-scattering spectra also confirmed the formation of ZnO nanoparticles. Abnormal longitudinal-optical (LO) phonon-dominant multiphonon Raman scattering was observed in the sample. Room-temperature photoluminescence (PL) spectra showed an ultraviolet emission peak at 374 nm. The origin of the ultraviolet emission is discussed here with the help of temperature-dependent PL spectra. The ultraviolet emission band was a mixture of free exciton and bound exciton recombination observed in the low temperature PL spectra (at 77 K). Abnormal temperature dependence of ultraviolet near-band-edge emission-integrated intensity of the sample was observed. The band tail state was observed in the absorption spectra, illustrating that the impurity-related defects were caused by the shell of the BaF2 grain layer. For comparison, ZnO films on BaF2 substrates were also fabricated by the magnetron sputtering method, and the same measurement methods were used.

Growth Spindle-Like ZnO Nanocrystalline Thin Films on Nickel Layers by Dc Magnetron Sputtering and its Thermal Annealing Properties

2011 ◽  
Vol 675-677 ◽  
pp. 1097-1100
Author(s):  
W. Wu ◽  
X.H. Xiao ◽  
T.C. Peng ◽  
C.Z. Jiang
Keyword(s):  
Thin Film ◽  
Magnetron Sputtering ◽  
Structural Features ◽  
Optical Quality ◽  
Zno Films ◽  
Near Band Edge ◽  
Band Edge Emission ◽  
Dc Magnetron Sputtering ◽  
Band Emission ◽  
Thin Film Layer

A novel spindle-like zinc oxide (ZnO) nanocrystalline thin film was successfully fabricated on Ni thin film layer by ultrahigh-vacuum dc magnetron sputtering. Then the as-grown films were annealed in air at various temperatures from 673 to 1073 K, the corresponding structural features and surface morphology were studied by X-ray diffraction (XRD) and field emission scanning electronic microscopy (FE-SEM). The results reveal that the dominant direction of grains movement changed from perpendicular to parallel to the film interfaces. A correlation of the band gap and photoluminescence (PL) properties of nanocrystalline ZnO films with particle size morphologies and strain was discussed. Especially, PL emission in UV range, which is due to near band edge emission is more intense in comparison with the green band emission (due to defect state) was observed in all samples, indicating a good optical quality of the deposited films.

Deposition of Zinc Oxide Thin Films Using a Surface Reaction on Platinum Nanoparticles

2011 ◽  
Vol 1315 ◽  
Author(s):  
Kanji Yasui ◽  
Hitoshi Miura ◽  
Hiroshi Nishiyama
Keyword(s):  
Free Exciton ◽  
Exothermic Reaction ◽  
Chemical Vapor ◽  
Band Edge ◽  
Chemical Vapor Deposition Method ◽  
Zno Films ◽  
Band Edge Emission ◽  
Edge Emission ◽  
Neutral Donor ◽  
Pl Spectra

ABSTRACTA new chemical vapor deposition method for the growth of ZnO films using the reaction between dimethylzinc (DMZn) and thermally excited H2O produced by a Pt-catalyzed H2–O2 reaction was investigated. The thermally excited H2O molecules formed by the exothermic reaction of H2 and O2 on the catalyst were ejected from a fine nozzle into the reaction zone and allowed to collide with DMZn ejected from another fine nozzle. The ZnO films were grown directly on a-plane (11-20) sapphire substrates at substrate temperatures of 773-873 K with no buffer layer. X-ray diffraction patterns exhibited intense (0002) and (0004) peaks from the ZnO(0001) index plane. The smallest full width at half maximum (FWHM) value of the ω- rocking curve of ZnO(0002) was less than 0.1º. The largest Hall mobility and the smallest residual carrier concentration of the ZnO films were 169 cm2V−1s−1 and 1.7×1017 cm−3, respectively. Photoluminescence (PL) spectra at room temperature exhibited a band edge emission at 3.29 eV, with a FWHM of 104 meV. Green luminescence from deeper levels was generally about 1.5% of the band edge emission intensity. PL spectra at 5 K showed a strong emission peak at 3.3603 eV, attributed to the neutral donor-bound exciton Dºx. The FWHM was as low as 1.0 meV. Free exciton emissions also appeared at 3.3757 eV (FXA, n=1) and 3.4221 eV (FXA, n=2).

Effect of Remote Hydrogen Plasma Treatment on ZnO Single Crystal Surfaces

2002 ◽  
Vol 744 ◽  
Author(s):  
Yuri M. Strzhemechny ◽  
John Nemergut ◽  
Junjik Bae ◽  
David C. Look ◽  
Leonard J. Brillson
Keyword(s):  
Single Crystal ◽  
Plasma Treatment ◽  
Hydrogen Plasma ◽  
Free Exciton ◽  
Chemical Vapor Transport ◽  
Near Band Edge ◽  
Band Edge Emission ◽  
Exciton Transition ◽  
Near Surface ◽  
Pl Spectra

ABSTRACTWe have studied the effects of hydrogen plasma treatment on the defect characteristics in single crystal ZnO grown at Eagle-Picher by chemical vapor transport. Depth-dependent cathodoluminescence (CL) spectra, temperature-dependent (9–300 K) and excitation intensity-dependent photoluminescence (PL) spectra reveal significant changes resulting from unannealed exposure of n-type ZnO to a remote hydrogen plasma. Low temperature PL spectra show that this hydrogen exposure effectively suppresses the free-exciton transition and redistributes intensities in the bound-exciton line set and two-electron satellites with their phonon replicas. The resultant spectra after hydrogenation exhibit a new peak feature at 3.366 eV possibly related to a neutral donor bound exciton. A simple thermal analysis of the activation energy for the 3.366 eV line yields 5–10 meV. Hydrogenation also produces a violet 100 meV-wide peak centered at 3.16 eV. Remote plasma hydrogenation produces similar changes in room-temperature CL spectra: near-band edge emission intensity increases with hydrogenation. Furthermore, this new emission increases with proximity to the free ZnO surfaces, i.e., with decreasing the energy of the incident electron beam from 3.0 down to 0.5 keV. Subsequent annealing at 450 °C completely restores both the PL and CL spectra in the sub-band gap range. The appearance of a new bound-exciton feature at 3.366 eV with H plasma exposure, the near-surface nature of the spectral changes, and the reversibility of spectral features with annealing indicate a direct link between H indiffusion and appearance of a shallow donor.

Lasing Characteristics of Nano-structured Zinc Oxide

2006 ◽  
Vol 957 ◽  
Author(s):  
Shou-Yi Kuo ◽  
Wei-Chun Chen ◽  
Fang-I Lai
Keyword(s):  
Electron Microscope ◽  
Room Temperature ◽  
Free Exciton ◽  
Laser Action ◽  
Hexagonal Structure ◽  
Zno Films ◽  
Near Band Edge ◽  
Lasing Characteristic ◽  
Pl Spectra ◽  
Reported Data

ABSTRACTHighy-quality nano-structured ZnO samples have been synthesized by simple chemical solution and post-thermal treatment. The samples were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), temperature-dependent photoluminescence (PL) spectra measurements. XRD patterns illustrated that there were no second phases in these ZnO samples, and the TEM results indicated that the ZnO samples are single crystalline with a hexagonal structure. Room-temperature PL spectra of ZnO thin films showed a strong UV near-band-edge (NBE) emission located at about 390 nm and a green defect-related (G) emissions, where the intensity ratio (INBE/IG) varies with the annealing temperatures. Meanwhile, the ZnO samples exhibited free exciton and very sharp exciton emissions at low temperatures. Particularly, room-temperature UV random lasing characteristic of ZnO films has been observed as well. It is shown that these nano-structured ZnO samples can exhibit random laser action depending on the growth condition. The threshold intensity for the lasing is comparable to earlier reported data. These results indicate that nano-structured ZnO samples prepared by simple techniques may be a promising material for further photonic devices. Possible lasing mechanism is discussed and further investigation to clarify the mechanism between the nano-structured ZnO samples is still underway.

Emission Diversity of ZnO Nanocrystals with Different Growth Temperatures

2014 ◽  
Vol 1675 ◽  
pp. 45-51
Author(s):  
E. Velázquez Lozada ◽  
T. Torchynska ◽  
G. Camacho González
Keyword(s):  
Free Exciton ◽  
Ultrasonic Spray Pyrolysis ◽  
Second Order ◽  
Zno Films ◽  
Near Band Edge ◽  
Phonon Replica ◽  
Ultrasonic Spray ◽  
Zno Nanocrystals ◽  
Order Diffraction ◽  
Different Temperatures

ABSTRACTScanning electronic microscopy (SEM), X ray diffraction (XRD) and photoluminescence (PL) have been applied to the study of structural and optical properties of ZnO nanocrystals prepared by the ultrasonic spray pyrolysis (USP) at different temperatures. The variation of temperatures and times at the growth of ZnO films permits modifying the ZnO phase from the amorphous to crystalline, to change the size of ZnO nanocrystals (NCs), as well as to vary their photoluminescence spectra. The study has revealed three types of PL bands in ZnO NCs: defect related emission, the near-band-edge (NBE) PL, related to the LO phonon replica of free exciton (FE) recombination, and its second-order diffraction peaks. The PL bands, related to the LO phonon replica of FE, and its second-order diffraction in the room temperature Pl spectrum testify on the high quality of ZnO films prepared by the USP technology.

scholarly journals Influence of the First Preparation Steps on the Properties of GaN Layers Grown on 6H-SiC by MBE

1999 ◽  
Vol 4 (S1) ◽  
pp. 310-315 ◽  
Author(s):  
R. Lantier ◽  
A. Rizzi ◽  
D. Guggi ◽  
H. Lüth ◽  
B. Neubauer ◽  
...  
Keyword(s):  
Substrate Surface ◽  
Free Exciton ◽  
Near Band Edge ◽  
Band Edge Emission ◽  
Edge Emission ◽  
Rocking Curve ◽  
A Value ◽  
Dislocations Density ◽  
Aln Buffer ◽  
Atomically Flat

The Gan heteroepitaxy on 6H-SiC is affected by the bad morphology of the substrate surface. We performed a hydrogen etching at 1550oC on the 6H-SiC(0001) substrates to obtain atomically flat terraces. An improvement of the structural properties of GaN grown by MBE on such substrates after deposition of a LT-AlN buffer layer is observed. A value of less than 220 arcsec of the FWHM of the XRD rocking curve, showing a reduced screw dislocations density, is comparable with the best results reported until now for thick GaN samples. Photoluminescence showed a structured near band edge emission spectrum with evidence of the A, B and C free exciton recombinations.

scholarly journals Study of Ultraviolet Emission Spectra in ZnO Thin Films

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Y. M. Lu ◽  
X. P. Li ◽  
P. J. Cao ◽  
S. C. Su ◽  
F. Jia ◽  
...  
Keyword(s):  
Thin Films ◽  
Low Temperature ◽  
Free Exciton ◽  
Emission Spectra ◽  
Low Energy ◽  
Zno Thin Films ◽  
Ultraviolet Emission ◽  
Exciton Transition ◽  
Pl Spectra ◽  
Uv Emission

Photoluminescence (PL) of ZnO thin films prepared on c-Al2O3substrates by pulsed laser deposition (PLD) are investigated. For all samples, roomtemperature (RT) spectra show a strong band-edge ultraviolet (UV) emission with a pronounced low-energy band tail. The origin of this UV emission is analyzed by the temperature dependence of PL spectra. The result shows that the UV emission at RT contains different recombination processes. At low temperature donor-bound exciton (D0X) emission plays a major role in PL spectra, while the free exciton transition (FX) gradually dominates the spectrum with increasing temperatures. It notes that at low temperature an emission band (FA) appears in low energy side of D0X and FX and can survive up to RT. Further confirmation shows that the origin of the band FA can be attributed to the transitions of conduction band electrons to acceptors (e, A0), in which the acceptor binding energy is estimated to be approximately 121 meV. It is concluded that at room temperature UV emission originates from the corporate contributions of the free exciton and free electrons-to-acceptor transitions.

scholarly journals Excitons in PL spectra of Cu(In, Ga)Se-=SUB=-2-=/SUB=- single crystal -=SUP=-*-=/SUP=-

2019 ◽  
Vol 61 (5) ◽  
pp. 1002
Author(s):  
E. Skidchenko ◽  
M.V. Yakushev ◽  
L. Spasevski ◽  
P.R. Edwards ◽  
M.A. Sulimov ◽  
...  
Keyword(s):  
Single Crystals ◽  
Free Exciton ◽  
Excitation Intensity ◽  
Structural Quality ◽  
Near Band Edge ◽  
Bridgman Technique ◽  
Pl Spectra ◽  
Vertical Bridgman ◽  
Ga Content

AbstractA photoluminescence (PL) study of Cu(In,Ga)Se_2 (CIGSe) single crystals, (grown by the vertical Bridgman technique) with the [Ga]/[Ga + In] ratio of 7 and 12% and the [Cu]/[In + Ga] ratio greater than unity, as measured by energy dispersive spectroscopy, is presented. Analysis of the excitation intensity and temperature dependence of the PL spectra suggested the excitonic nature of the observed near-band-edge emissions peaks. Free and bound excitons in CIGSe single crystals with both 7 and 12% Ga content are clearly observed, analyzed and identified. An activation energy of 19 meV is determined for the free exciton in the PL spectra of the sample with 12% Ga. The presence of the excitons demonstrated a high structural quality of the material.

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