The Effects of Thermal Treatments on Microstructure Phosphorus-Doped ZnO Layers Grown by Thermal Evaporation

The ZnO films doped with 3 wt% phosphorus (P) were produced by activating phosphorus doped ZnO (ZnO:P) thin films in oxygen (O₂) ambient at 600°C for 30, 60, 90 and 120 min, respectively. As-deposited films doped with phosphorus are highly conductive and n type. All the films showed p-type conduction after annealing, in an O₂ ambient atmosphere. The activation energies of the phosphorus dopant in the p-type ZnO under O₂ ambient gases indicate that phosphorus substitution on the O site yielded a deep level in the gap. With a further increase of the annealed durations, the crystalline quality of the ZnO:P sample is degraded. The best p-type ZnO:P film deposited at 600°C for 30 min shows a resistivity of 1.85 Ω cm and a relatively high hole concentration of 5.1 × 10¹⁷cm^–3 at room temperature. The films exhibit a polycrystalline hexagonal wurtzite structure without preferred orientation. The mean grain sizes are calculated to be about 60, 72, 78, 85 and 90 nm for the p-type ZnO films prepared at 600°C for 30, 60, 90 and 120 min, respectively. Room temperature photoluminescence (PL) spectra of the ZnO film exhibit two emission bands — paramount excitonic ultraviolet (UV) emission and weak deep level visible emission. The excellent emission from the film annealed at 600°C for 30 min is attributed to the good crystalline quality of the p-type ZnO film and the low rate of formation of intrinsic defects at such short duration. The visible emission consists of two components in the green range.     

Pulsed laser deposition of Zr–N codoped <Emphasis Type="Italic">p</Emphasis>-type ZnO thin films

Present p-type ZnO films tend to exhibit high resistivity and low carrier concentration, and they revert to their natural n-type state within days after deposition. One approach to grow higher quality p-type ZnO is by codoping the ZnO during growth. This article describes recent results from the growth and characterization of Zr–N codoped p-type ZnO thin films by pulsed laser deposition (PLD) on (0001) sapphire substrates. For this work, both N-doped and Zr–N codoped p-type ZnO films were grown for comparison purposes at substrate temperatures ranging between 400 to 700 °C and N₂O background pressures between 10⁻⁵ to 10⁻² Torr. The carrier type and conduction were found to be very sensitive to substrate temperature and N₂O deposition pressure. P-type conduction was observed for films grown at pressures between 10⁻³ to 10⁻² Torr. The Zr–N codoped ZnO films grown at 550 °C in 1×10⁻³ Torr of N₂O show p-type conduction behavior with a very low resistivity of 0.89 Ω-cm, a carrier concentration of 5.0×10¹⁸ cm⁻³, and a Hall mobility of 1.4 cm² V⁻¹ s⁻¹. The structure, morphology and optical properties were also evaluated for both N-doped and Zr–N codoped ZnO films.     

Photoluminescence and absorption in sol-gel-derived ZnO films

Highly c-axis-oriented ZnO films were obtained on corning glass substrate by sol-gel technique. The characteristics of photoluminescence (PL) of ZnO, as well as the exciton absorption in the absorption (UV) spectra are closely related to the post-annealing treatment. The difference between PL peak position and the absorption edge, designated as Stokes shift, is found to decrease with the increase of annealing temperature. The minimum Stokes shift is about 150 meV. The decrease of Stokes shift is attributed to the decrease in carrier concentration in ZnO film with annealing. X-ray diffraction, surface morphology and refractive index results indicate an improvement in crystalline quality with annealing. Annealed films also exhibit a green emission centered at ∼520 nm with activation energy of 0.89 eV. The green emission is attributed to the electron transition from the bottom of the conduction band to the antisite oxygen O_Zn defect levels.     

Effects of Annealing Temperature on Structural and Optical Properties of ZnO Thin Films

The effects of annealing temperature on the structural and optical properties of ZnO films grown on Si （100） substrates by sol-gel spin-coating are investigated. The structural and optical properties are characterized by x-ray diffraction, scanning electron microscopy and photoluminescence spectra. X-ray diffraction analysis shows the crystal quality of ZnO films becomes better after annealing at high temperature. The grain size increases with the temperature increasing. It is found that the tensile stress in the plane of ZnO films first increases and then decreases with the annealing temperature increasing, reaching the maximum value of 1.8 GPa at 700℃. PL spectra of ZnO films annealed at various temperatures consists of a near band edge emission around 380 nm and visible emissions due to the electronic defects, which are related to deep level emissions, such as oxide antisite （OZn）, interstitial oxygen （Oi）, interstitial zinc （Zni） and zinc vacancy （VZn^-）, which are generated during annealing process. The evolution of defects is analyzed by PL spectra based on the energy of the electronic transitions.     

Structural,optical and electrical properties of post annealed Mg doped ZnO films for optoelectronics applications

Mg _x Zn_1-x O films with 0.15 mole composition of Magnesium were successfully deposited by the spin coating sol–gel method. Zinc acetate dihydrate and Magnesium acetate were used as starting precursors to prepare the solution in ethanol solvent. The MgZnO films were deposited on microscopic glass substrates and post annealed at three different temperatures. X-ray Diffractometer (XRD), Scanning Electron Microscopy (SEM) and UV–VIS Spectrophotometer were used to characterize the deposited films for studying structural and optical properties. Energy dispersive analysis by X-ray (EDAX) was used to determine incorporation of Mg content in ZnO films. XRD spectrum reveals that, the deposited Mg doped ZnO films were polycrystalline in nature. The intensity of c-axis in the XRD spectrum goes on decreasing as Mg composition slightly increasing corresponding to increase in annealing temperature. EDAX spectra clearly showed the incorporation of Mg into the ZnO films. Semiconductor characterization system was used for the I–V characterization of MgZnO films. I–V characteristics show decrease in current as increase in the biased voltage. Optical band gap of MgZnO films was found to be increased from 3.2 to 3.38 eV as estimated from the absorption coefficients.     

White-light emission from annealed ZnO:Si nanocomposite thin films

As grown ZnO:Si nanocomposites of different compositional ratios were fabricated by thermal evaporation techniques. These films were subjected to post-deposition annealing under high vacuum at a temperature of 250 °C for 90 min. The photoluminescence (PL) spectra of annealed samples have shown marked improvements both in terms of intensity and broadening. Structural and Raman analyses show formation of a Zn–Si–O shell around ZnO nanoclusters wherein on heating Zn₂SiO₄ compound forms resulting in huge UV, orange and red peaks at 310, 570 and 640 nm in PL. The new emissions due to Zn₂SiO₄ completes white light spectrum. The study not only suggests that 1:2 ratio is the best suited for material manipulation but also shows process at the interface of ZnO nanoclusters and silicon matrix leads to new PL emissions.     

Comparative study on structural and optical properties of ZnO thin films prepared by PLD using ZnO powder target and ceramic target

Zinc oxide thin films have been obtained in O₂ ambient at a pressure of 1.3 Pa by pulsed laser deposition (PLD) using ZnO powder target and ceramic target. The effect of temperature on structural and optical properties of ZnO thin films was investigated systematically by XRD, SEM, FTIR and PL spectra. The results show that the best structural and optical properties can be achieved for ZnO thin film fabricated at 700 °C using powder target and at 400 °C using ceramic target, respectively. The PL spectrum reveals that the efficiency of UV emission of ZnO thin film fabricated by using powder target is low, and the defect emission of ZnO thin film derived from Zn_i and O_i is high.     

Burstein–Moss shift and room temperature near-band-edge luminescence in lithium-doped zinc oxide

Nanopowders of pure and lithium-doped semiconducting ZnO (Zn_1−x Li _x O, where x= 0, 0.01, 0.03, 0.06, 0.09 and 0.15 in atomic percent (at.%)) are prepared by PEG-assisted low-temperature hydrothermal method. The average crystallite size is calculated using Debye–Scherrer formula and corrected for strain-induced broadening by Williamson–Hall (W–H) plot. The peak shift in XRD and the lattice constant of ZnO as a function of unit cell composition are predicted by Vegard’s law. The evolution of ZnO nanostructures from rod-shaped to particle nature is observed from TEM images and the influence of dopant on the morphology is investigated. The optical absorption measurement marks an indication that the incorporation of lithium ion into the lattice of ZnO widens the optical band gap energy from ∼2.60 to ∼3.20 eV. The near band edge (NBE) emission peak centered at ∼3.10 eV is considered to be the dominant emission peak in the PL spectra. Blue emission peak is not observed in doped ZnO, thus promoting defect-free nanoparticles. The Burstein–Moss shift serves as a qualitative tool to analyze the widening of the optical band gap and to study the shape of the NBE luminescence in doped ZnO nanopowders. FT-IR spectra are used to identify the strong metal–oxide (Zn–O) interaction.     

Influence of Al concentration on electrical, structural and optical properties of Al-As codoped p-ZnO thin films

We report the influence of Al concentration on electrical, structural, optical and morphological properties of Al-As codoped p-ZnO thin films using RF magnetron sputtering. Al-As codoped p-ZnO films with different Al concentrations were fabricated using As back diffusion from the GaAs substrate and sputtering Al₂O₃ mixed ZnO targets (1, 2 and 4 at%). The grown films were investigated by Hall effect measurement, X-ray diffraction (XRD), electron probe microanalysis (EPMA), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and atomic force microscopy (AFM) to study the electrical, structural, optical and morphological properties of the films. From the XRD, it was observed that both full-width at half-maximum (FWHM) and c-axis lattice constant have similar trends with respect to Al concentration. Hall measurements showed that the hole concentration increases as the Al concentration increases from 10¹⁵ to 10²⁰ cm⁻³. The increase in hole concentration upon codoping was supported by the red shift in the near-band-edge (NBE) emission observed from room temperature PL spectra. The proposed p-type mechanism due to As_Zn-2V_Zn complex was confirmed by low temperature PL and XPS analysis. The low FWHM, resistivity and peak-to-valley roughness observed by XRD, Hall measurement and AFM, respectively, suggest that 1 at% Al-doped ZnO:As film is the best codoped film.     

Visible photoluminescence from Ge+-implanted SiO2 films thermally grown on crystalline Si

+ -implanted SiO₂ films is studied as a function of different fabricating conditions (implantation dose, annealing temperature and time). The SiO₂ films containing Ge nanocrystals exhibit two photoluminescence (PL) bands peaked at 600 nm and 780 nm. There are two excitation bands in the PL excitation (PLE) spectra. With variation in Ge nanocrystal size, the PL and PLE peak energies show no appreciable shift. The PL and PLE spectral analyses suggest that during the PL process, electron–hole pairs are generated by the E(l) and E(2) direct transitions inside Ge nanocrystals, which then radiatively recombine via luminescent centers in the matrix or at the interface between the nanocrystal/matrix. Received: 27 January 1998/Accepted: 18 March 1998     

Single violet luminescence emitted from ZnO films obtained by oxidation of Zn film on quartz glass

The photoluminescence (PL) emission properties of ZnO films obtained on quartz glass substrate by the oxidation of Zn films were studied. The strong single violet emission centering about 413-424 nm was observed in the room temperature PL spectra of the ZnO films. The intensity of violet emission increased and the peak position shift from 424 to 413 nm with increasing oxygen pressures. The violet emission was attributed to the electron transition from the valence band to interstitial zinc (Zn_i) level under low oxygen pressure conditions (50-500 Pa). Under high oxygen pressure conditions (5000-23,000 Pa), both interstitial zinc (Zn_i) and zinc Vacancy (V_Zn) were thought to be responsible for the violet emission.     

Effect of the annealing environment on the optical properties of ZnO/GaAs grown by MOCVD

The optical properties of ZnO grown on (1 0 0) GaAs substrate using metalorganic chemical vapor deposition are investigated by photoluminescence (PL) spectroscopy. Postgrowth annealing in nitrogen and oxygen was performed for different times and temperatures in order to incorporate As from the substrate into the ZnO thin films. The PL spectra of the samples annealed in different ambients reveal that the effect of As diffusion into the ZnO thin films is more pronounced when the annealing is performed in oxygen at 550 °C. The 11 K PL spectra show the appearance of a transition at ∼3.35 eV after annealing in oxygen at 550 °C for 1 h. A further increase in the annealing temperature leads to the disappearance of this line, while for annealing times longer than 2 h at 550 °C, it is no longer prominent. The increase in intensity of this new transition is also accompanied by the enhancement of radiative centers related to structural defects, such as the stacking fault-related transition at 3.31 eV and the Y-line. Temperature dependent PL illustrates the excitonic nature of the new transition at ∼3.35 eV, which is therefore assigned to (A⁰, X) transition, where the acceptor is possibly the 2V_Zn-As_Zn complex, with an activation energy E_A in the range of 160-240 meV. Furthermore, the enhancement of the radiative centers related to structural defects is regarded as evidence that As atoms tend to segregate in the vicinity of structural defects to relieve local strain.     

Structural and PL properties of Cu-doped ZnO films

Cu-doped ZnO films with hexagonal wurtzite structure were deposited on silicon (1 1 1) substrates by radio frequency (RF) sputtering technique. An ultraviolet (UV) peak at ∼380 nm and a blue band centered at ∼430 nm were observed in the room temperature photoluminescent (PL) spectra. The UV emission peak was from the exciton transition. The blue emission band was assigned to the Zn interstitial (Zn_i) and Zn vacancy (V_Zn) level transition. A strong blue peak (∼435 nm) was observed in the PL spectra when the α_Cu (the area ratio of Cu-chips to the Zn target) was 1.5% at 100 W, and ZnO films had c-axis preferred orientation and smaller lattice mismatch. The influence of α_Cu and the sputtering power on the blue band was investigated.     

衬底温度对PLD法生长的Mg0.05Zn0.95O薄膜结构和发光特性的影响

用脉冲激光沉积(PLD)法在不同温度的Si(111)衬底上成功制备了c轴择优取向的Mg_005Zn_095O薄膜.通过X射线衍射(XRD)和光致发光谱(PL)研究了衬底温度对Mg_005Zn_095O薄膜结构和发光特性的影响,探讨了薄膜的结晶质量与发光特性之间的关系.结果表明,在衬底温度为450℃时生长的Mg_005Zn_095O薄膜具有很好的c轴取向和较强的光致发光峰.室温下分别用激发波长为240,300和325nm的氙灯作为激发光源得到不同样品的PL谱,分析表明紫外发光峰和紫峰来源于自由激子的复合辐射且发光强度与薄膜的结晶质量密切相关,蓝绿发光峰与氧空位有关.此外,探讨了衬底温度影响紫外光致发光峰红移和蓝移的可能机理. 关键词： 005Zn_095O薄膜')" href="#">Mg_005Zn_095O薄膜 PLD 衬底温度 光致发光     

非掺杂ZnO薄膜中紫外与绿色发光中心

用直流反应溅射方法在硅衬底上淀积了ZnO薄膜,测量它们的光致发光(PL)光谱,观察到两个发光峰,峰值能量分别为3.18(紫外峰,UV)和2.38eV(绿峰).样品用不同温度分别在氧气、氮气和空气中热处理后,测量了PL光谱中绿峰和紫外峰强度随热处理温度和气氛的变化,同时比较了用FP-LMT方法计算的ZnO中几种本征缺陷的能级位置.根据实验和能级计算的结果,推测出ZnO薄膜中的紫外峰与ZnO带边激子跃迁有关,而绿色发光主要来源于导带底到氧错位缺陷(O_Zn)能级的跃迁,而不是通常认为的氧空 关键词： ZnO薄膜 热处理 光致发光光谱 缺陷能级     

Transitions of microstructure and photoluminescence properties of the Ge/ZnO multilayer films in certain annealing temperature region

The Ge/ZnO multilayer films have been prepared by rf magnetron sputtering. The effects of annealing on the microstructure and photoluminescence properties of the multilayers have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) spectrometry and photoluminescence (PL) spectrometry. The investigation of structural properties indicates that Zn₂GeO₄ has been formed with (2 2 0) texture and Zn deficiency from Ge/ZnO multilayer films in the process of annealing. However, lower Zn/Ge ratio can be improved by annealing. The annealed multilayers show three main emission bands at 532, 700, and 761 nm, which originate from the transition between oxygen vacancy () and Zn vacancies (V_Zn), the radiative recombination of quantum-confined excitons (QCE) in Ge nanocrystals, and the optical transition in the GeO color centers, respectively. Finally, the fabrication of thin film Zn₂GeO₄ from Ge/ZnO multilayer films by annealing at low temperature provides another approach to prepare the green-emitting oxide phosphor film:Zn₂GeO₄:Mn.     

Influence of post-deposition annealing on the structural,optical and electrical properties of Li and Mg co-doped ZnO thin films deposited by sol–gel technique

Lithium (Li) and magnesium (Mg) co-doped zinc oxide (ZnO) thin films were deposited by sol–gel method using spin coating technique. The films were deposited on glass substrates and annealed at different temperatures. The effects of annealing temperature on the structural, optical and electrical properties of the deposited films were investigated using X-ray diffraction (XRD), Ultraviolet–Visible absorption spectra (UV–VIS), photoluminescence spectra (PL), X-ray photo electron spectroscopy (XPS) and Hall measurements. XRD patterns indicated that the deposited films had a polycrystalline hexagonal wurtzite structure with preferred (0 0 0 2) orientation. All films were found to exhibit a good transparency in the visible range. Analysis of the absorption edge revealed that the optical band gap energies of the films annealed at different temperatures varies between 3.49 eV and 3.69 eV. Room temperature PL spectra of the deposited films annealed at various temperatures consist of a near band edge emission and visible emission due to the electronic defects, which are related to deep level emissions, such as oxide antisite (O_Zn), interstitial zinc (Zn_i), interstitial oxygen (O_i) and zinc vacancy (V_Zn) which are generated during annealing process. The influence of annealing temperature on the chemical state of the dopants in the film was analysed by XPS spectra. Ion beam analysis (Rutherford back scattering) experiments were performed to evaluate the content of Li and Mg in the films. Hall measurements confirmed the p-type nature of the deposited films.     

Luminescence of CsBr:Eu films grown by liquid-phase epitaxy

By liquid-phase epitaxy from an aqueous alcoholic solution, we have obtained films of the well-known storage phospor CsBr:Eu, and we have studied their cathodoluminescence and photoluminescence (PL) spectra compared with the undoped CsBr films. We have established that the structure of the photoluminescence centers of the CsBr:Eu films when excited by laser radiation in the absorption band of the Eu²⁺ ions (λ = 337 nm) includes Eu²⁺-V_Cs isolated dipole centers and CsEuBr₃ aggregate centers, and also luminescence centers based on inclusions of hydroxyl group OH⁻ with the corresponding emission bands in the 440 nm, 520 nm, and 600 nm regions. We have studied the dependence of the spectra and the intensity of the photoluminescence for CsBr:Eu films on annealing temperature in air at 423–483 K, compared with analogous dependences for CsBr:Eu single crystals obtained from the melt. We have shown that annealing the films at T = 423–463 K leads to rapid formation of CsEuBr3 aggregate luminescence centers, while for T > 473 K thermal degradation of these centers occurs. We conclude that the observed differences between the photoluminescence spectra of CsBr:Eu films and CsBr:Eu single crystals may be due to additional doping of the films with OH⁻ ions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 191–194, March–April, 2006.     

Effects of S incorporation on Ag substitutional acceptors in ZnO:(Ag, S) thin films

Ag–S codoped ZnO thin films have been fabricated on Si substrates by radio frequency (RF) magnetron sputtering using a thermal oxidation method. XRD and SEM measurements showed that the sample has hexagonal wurtzite structure with a preferential (002) orientation and the surface is composed of compact and uniform grains. Ag_Zn–nS_O defect complexes were observed in the Ag–S codoped ZnO films by XPS analysis. Low temperature PL spectra showed neutral acceptor bound exciton emission related to Ag_Zn–nS_O. The corresponding acceptor ionization energy of 150 meV is much lower than that of monodoped Ag (246 meV), which is favorable for p-type doping of ZnO.     

Effect of Ag doping on the photoluminescence properties of ZnO films

ZnO:Ag films were grown on Si (1 0 0) substrates by ultrasonic spray pyrolysis at various substrate temperatures. The effect of deposition temperature on the structural and the room temperature photoluminescence (RT-PL) properties of ZnO:Ag films was studied. With the deposition temperature rising to 550 °C, the intensity of the near-band edge (NBE) emission at 378 nm decreased and a new emission peak at 399 nm was observed. On the basis of the X-ray diffraction pattern (XRD), the X-ray photoelectron (XPS) spectra of ZnO:Ag films, and the effects of annealing on the PL, we suggest that the 399 nm emission should be attributed to the electron transition from the conduction band to Ag_Zn-related complexes defects radiative centers above the valence band.