Structural and luminescent properties of ZnO:P films produced by annealing ZnP<Subscript>2</Subscript> wafers in atomic oxygen

The epitaxial ZnO:P films are fabricated by annealing the ZnP₂ wafers in atomic oxygen (oxygen radicals). The properties of the films are studied by X-ray diffraction analysis, atomic force microscopy, Auger spectroscopy, and photoluminescence measurements. In the X-ray diffraction spectra of the samples, the (002) peak is observed, suggesting that the ZnO:P films are oriented along the c axis. The Auger spectroscopy data show that the ZnO films contain phosphorus. The low-temperature photoluminescence spectrum observed for the ZnO: P films exhibits a 3.356 eV peak presumably corresponding to excitons bound at neutral acceptors and a peak at 3.306 eV (free electron)-acceptor transitions associated with the P_O level. The phosphorus related acceptor level is localized at 128 meV above the top of the valence band. The origin of the 3.312 eV band related to recombination at donor-acceptor pairs is discussed.     

Investigation of the blue–green emission and UV photosensitivity of Cu-doped ZnO films

Cu-doped zinc oxide (ZnO:Cu) films were deposited on p-Si (100) substrates using radio-frequency reactive magnetron sputtering. The structure and optical properties of the films were characterized by X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and fluorescence spectroscopy. XRD and SEM results revealed that ZnO:Cu film had a better preferential orientation along the c-axis compared with pure ZnO film. The chemical state of copper and oxygen in ZnO:Cu films was investigated by XPS. The results suggest that the Cu ion has a mixed univalent and bivalent state. The integrated Cu²⁺/Cu⁺ intensity ratio increased with the O₂ partial pressure. Photoluminescence measurements at room temperature revealed a double peak in the blue regions and a green emission peak. The close relationship between the valence state of Cu ions and the blue–green emission is discussed in detail. A higher photocurrent was observed for ZnO:Cu films under UV illumination. UV photodetectors based on ZnO:Cu films have high sensitivity and fast response and recovery times. Under periodic UV illumination at 380 nm the ZnO:Cu films showed stable photocurrent growth and decay, so the films are potential candidate materials for UV photodetectors.     

Structural and optical properties of ZnO films produced by a nonvacuum chemical technique

Zinc-oxide films are grown by a new nonvacuum chemical method: the pyrolysis of zinc acetylacetonate at a temperature of 280–300°C. The structural, phonon, and emission properties of the ZnO films are studied by X-ray diffraction analysis, scanning electron microscopy, Raman measurements, and photoluminescence spectroscopy. The high-intensity (0002) peak recorded in the X-ray diffraction spectra indicate the predominant orientation of crystallites in the (0001) direction in the ZnO films. From analysis of the E ₂ ^high mode in the Raman spectrum of the ZnO films, the elastic strains ? _zz (～3.2 × 10^?3) and the quality of the crystal structure are determined. The characteristics of the pyrolytic ZnO films are compared with the corresponding characteristics of ZnO films grown by molecular-beam epitaxy. As a result, the possibility of growing polycrystalline ZnO films of rather high quality by a practically feasible low-temperature technique is demonstrated.     

未掺杂GaN外延膜的结晶特性与蓝带发光关系的研究

采用卢瑟福背散射／沟道技术，X射线双晶衍射技术和光致发光技术对几个以MOCVD技术生长的蓝带发光差异明显的未掺杂GaN外延膜和GaN：Mg外延膜进行了测试。结果表明，未掺杂GaN薄膜中出现的2．9eV左右的蓝带发光与薄膜的结晶品质密切相关。随未掺杂GaN的蓝带强度与带边强度之比增大，GaN的卢瑟福背散射／沟道谱最低产额增大，X射线双晶衍射峰半高宽增大。未掺杂GaN薄膜的蓝带发光与薄膜中的某种本征缺陷有关。研究还表明，未掺杂GaN中出现的蓝带与GaN：Mg外延膜中出现的2．9eV左右的发光峰的发光机理不同。     

Influences of ZnO buffer layers on the quality of ZnO films synthesized by the metal-organic chemical vapor deposition process

High-quality ZnO thin films were prepared by metal-organic chemical vapor deposition (MOCVD) on a sapphire (a-Al₂O₃) substrate. The synthesis of ZnO films was performed over a substrate temperature of 400–700°C and at chamber pressures of 0.1–10 torr. The structural and optical properties of ZnO films were investigated in terms of deposition conditions, such as substrate temperature, working pressure, and the ratio of Zn precursor (Diethylzinc (DEZn)) to oxygen. The ZnO films, preferentially oriented to 34.42° diffraction because of the (002) plane, were obtained under processing conditions of 700°C and 3 torr. This film shows a full-width at half-maximum (FWHM) of 0.4–0.6°. The results of photoluminescence (PL) spectroscopy also show a strong near band-edge emission at 3.36 eV at 10 K as well as a very weak emission at deep levels around 2.5 eV at room temperature. In addition, we are interested in the introduction of ZnO buffer-layer growth by the sputtering process to reduce lattice mismatch stress. This paper addresses how to advance the crystalline and optical properties of film. The ZnO film grown with the aid of a buffer layer shows a FWHM of 0.06–0.1° in the x-ray diffraction (XRD) pattern. This result indicates that crystalline properties were highly improved by the ZnO buffer layers. The PL spectroscopy data of ZnO film also shows a strong near band-edge emission and very weak deep-level emission similar to films synthesized without a buffer layer. Accordingly, synthesized ZnO films with buffer layers indicate fairly good optical properties and low defect density as well as excellent crystallinity.     

Effect of Lattice Mismatch on Luminescence of ZnO/Si Hetero-Structure

研究了ZnO薄膜中应力对发光的影响.实验样品为ZnO体单晶、在Si基片上直接生长的ZnO薄膜以及通过SiC过渡层在Si基片上生长的ZnO薄膜.测量了这三种样品的X射线衍射图形、喇曼光谱和光致发光光谱.由X射线衍射图形可以看出,由于SiC过渡层缓解了ZnO与Si之间的晶格失配,使得通过SiC过渡层在Si上生长的ZnO薄膜的结晶质量好于直接在Si上生长的ZnO薄膜的质量.进一步通过喇曼谱测量发现,与ZnO体单晶相比,直接在Si上生长的ZnO薄膜的E2(high)峰红移1.9cm-1,根据喇曼谱峰位移与应力的关系可以推出薄膜中存在0.4GPa的张应力;而通过SiC过渡层在Si上生长的ZnO薄膜的E2(high)峰红移0.9cm-1,对应着0.2GPa的张应力.对照X射线衍射图形的结果可以看出,薄膜中张应力的大小与薄膜的结晶质量密切相关,表明张应力来源于外延层和基片间的晶格失配,晶格失配越大,外延层中产生的张应力越大.有无SiC过渡层的两种薄膜样品的PL光谱中都存在紫外和绿光两种谱带,随样品热处理时氧气分压增加,两种样品都出现绿光增强的相似的变化规律,但有SiC过渡层的样品的变化幅度较小.这一结果说明,绿色发光中心与薄膜的质量,也就是与薄膜中存在的张应力大小有关.在以往研究中得出的非故意掺杂ZnO薄膜的绿色发光中心来源于氧反位缺陷(Ozn),文中研究的结果正好可以解释氧反位缺陷形成的原因.由于薄膜中存在张应力,使得样品的能量升高,其结果必然会产生缺陷来释放张应力,以便降低系统能量.而氧离子半径大于锌离子半径,氧替位锌有利于释放张应力,也就是说,在存在张应力的情况下,Ozn的形成能降低.这一结果进一步证明Si上生长的ZnO薄膜中的绿色发光中心与氧反位缺陷有关.     

Properties of ZnO Thin Films Codoped with Lithium and Phosphorus

The properties of ZnO thin films codoped with lithium and phosphorus have been characterized. The films were deposited from high-purity ZnO and Li₃PO₄ solid targets onto c-plane sapphire substrates by radiofrequency (RF) magnetron sputtering. A substrate temperature of 900°C was determined as optimum for depositing undoped ZnO films with background electron concentration of 9.9 × 10¹⁵ cm^?3 as the buffer layer on the sapphire substrate. Postdeposition annealing was carried out using rapid thermal processing in O₂ at temperatures ranging from 500°C to 1000°C for 3 min. Analyses performed using low-temperature photoluminescence spectroscopy measurements revealed luminescence peaks at 3.356 eV, 3.307 eV, 3.248 eV, and 3.203 eV at 12 K for the codoped samples. X-ray diffraction 2θ-scans showed a single peak at about 34.4° with full-width at half-maximum of about 0.09°. Hall-effect measurements revealed initial p-type conductivities, but these were unstable and toggled between p-type and n-type over time with Hall concentrations that varied between 2.05 × 10¹³ cm^?3 and 2.89 × 10¹⁵ cm^?3. The fluctuation in the carrier type could be due to lateral inhomogeneity in the hole concentration caused by stacking faults in the films. An additional cause could be the small Hall voltages in the measurements, which could be significantly impacted by even small spikes in signal noise inherent in the measurements.     

Experimental and first-principles DFT studies of electronic,optical and magnetic properties of cerium–manganese codoped zinc oxide nanostructures

Syntheses, structural, optical and magnetic characterizations of codoped ZnO nanoparticles have been reported. Nanoparticles of Zn_1−2xCe_xMn_xO (x=0.00, 0.01, 0.02, 0.03, 0.04, and 0.05) were synthesized using a microwave-assisted combustion method. Structural, optical and magnetic properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL) and a vibrating sample magnetometer (VSM). The observed shift in XRD peak position, change in peak intensity, cell parameters, volume and stress confirmed the substitution of cerium-manganese (Ce–Mn) dopants within ZnO lattice. The synthesized nanoparticles show different microstructure without changing the parent hexagonal wurtzite structure of zinc oxide (ZnO). The average crystallites size was decreased from 43 to 21 nm. Energy dispersive X-ray spectra confirmed the presence of Ce and Mn in ZnO system and the weight percentage was nearly equal to their nominal stoichiometry. DRS analysis showed a decrease in the energy gap with increasing dopants content. The observed luminescence in the green, violet and blue regions strongly depends on the nature of the doping elements and their concentration owing to the formation of different oxygen vacancy, zinc interstitial, and surface morphology. Our results demonstrate that Mn ions doping concentration play an important role in the observed room temperature ferromagnetism (RTFM) of Ce–Mn codoped ZnO nanoparticles. First- principles calculation results indicate that Ce governs the stability, while Mn adjusts the magnetic characteristics in codoped ZnO.     

氧压对PLD制备掺铜ZnO薄膜光学性质的影响

为了研究生长氧压对ZnO薄膜的结构和光学性质的影响,采用脉冲激光沉积技术,在P-Si〈111〉衬底上制备了不同生长氧压下的掺铜ZnO薄膜.利用X射线衍射仪对样品的结构进行了分析,并用荧光分光光度计对样品的光致发光谱进行了测量.结果表明,所有样品均在2θ=34.3°附近出现ZnO(002)衍射峰,没有发现Cu的衍射峰,在...     

Studies of defect states of ZnO thin films under different annealing conditions

ZnO thin films were grown by the pulsed laser deposition technique on c-plane sapphire substrates at a substrate temperature of 500 °C with 1×10⁻⁴ Torr ambient gas. After the deposition process, ZnO thin films were annealed at 1000 °C for 5 min under N₂ or O₂ ambient gas, respectively. In the X-ray patterns, the (0 0 2) peak of the annealed sample was shifted from that of the as-grown sample, which indicates a reduced lattice constant of about 1%. Even though the X-ray diffraction patterns in the samples annealed under O₂ and N₂ annealing gases were almost the same, photoluminescence spectra showed the generation of a shallow level with a few meV, and deep-level states were generated at E_v+0.594 eV. In addition, a defect state appeared at E_c−0.607 eV, which originated from hydrogen plasma irradiation on the ZnO sample.     

The Influence of Film Thickness on the Transparency and Conductivity of Al-Doped ZnO Thin Films Fabricated by Ion-Beam Sputtering

To evaluate the influence of film thickness on the structural, electrical, and optical properties of Al-doped ZnO (AZO) films, a set of polycrystalline AZO samples with different thickness were deposited on glass substrates by ion-beam sputtering deposition (IBSD). X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive x-ray spectroscopy (EDS), four-point probe measurements, and spectrophotometry were used to characterize the films. XRD showed that all the AZO films had preferred c-axis orientation. The ZnO (110) peak appeared, and the intensity increased, with increasing thickness. All the samples exhibited compressive intrinsic stresses. AFM showed that the grain size along with the root-mean-square (RMS) roughness increased with increasing thickness. The decrease of resistivity is due to the corresponding change in grain size, surface morphology, and chemical composition. The average optical transmittance of the AZO films was over 80%, and a sharp fundamental absorption edge with red-shifting was observed in the visible region. The optical band gap decreased from 3.95 eV to 3.80 eV when the AZO film thickness increased from 100 nm to 500 nm.     

Post-annealing effects on structural and magnetic properties of Mn–N codoped ZnO thin films

The sputtered ZnO:Mn thin films were implanted with nitrogen ions (N⁺) and subsequently annealed at different temperatures up to 800 °C in N₂ atmosphere. The structural and magnetic properties of the samples were systematically investigated. Both x-ray diffraction and Raman analyses reveal that all the films are of the wurtzite structure of ZnO with no distinct evidence of secondary phases. X-ray photoelectron spectroscopy studies indicate that both Mn²⁺ and N³⁻ ions were incorporated into ZnO lattice successfully. While the films without nitrogen ions show paramagnetic behavior, ferromagnetism with clear hysteresis at 300 K is observed in Mn–N codoped ZnO films. Most importantly, we also found that the magnetic behavior of the codoped ZnO is very sensitive to the annealing temperature due to its effect on the activation of nitrogen ions. The strongest ferromagnetism is obtained in the films with the highest amount of nitrogen ions acceptors. Our results support the predication that the ferromagnetic ZnO:Mn²⁺ should be more stable of a hole-rich environment by theory.     

Optical properties of Zr and ZrO2 films deposited by laser ablation

Optical properties of Zr and ZrO₂ films in the energy range from 1.5 to 100 eV were obtained by quantitative analysis of reflection electron energy loss spectroscopy (REELS) and ellipsometry. The films were prepared on (1 1 1) silicon substrates by reactive laser ablation using a zirconium target. For the growth of ZrO₂ films a pressure of 5 mTorr of oxygen in the growth chamber was used. The substrate temperature during deposition was . The deposits were studied ex situ by X-ray diffraction (XRD) and in situ by X-ray photoelectron spectroscopy (XPS) and REELS. The ZrO₂ films were found to be polycrystalline with monoclinic structure. The XPS results showed that the oxygen pressure used is the optimal control to produce ZrO₂ films by laser ablation. A gap of 5 eV for the ZrO₂ film was measured by REELS.     

Effect of Thermal Annealing on the Characteristics of Phosphorus-Implanted ZnO Crystals

A P-doped ZnO surface layer on undoped ZnO wafers was prepared by phosphorus (P) ion implantation. Hall effect measurement revealed p-type conduction in such layers annealed at 800°C. This indicates that acceptor levels are present in P-doped ZnO, even though the ZnO is still n-type. Micro-Raman scattering in ?z(xy)z geometry was conducted on P-implanted ZnO. The E ₂ ^high mode shift observed toward the high-energy region was related to compressive stress as a result of P-ion implantation. This compressive stress led to the appearance of an A ₁(LO) peak, which is an inactive mode. This A ₁(LO) peak relaxed during thermal annealing in ambient oxygen at temperatures higher than 700°C. The P2p_3/2 peak observed at 135.6 eV by x-ray photoelectron spectroscopy is associated with chemical bond formation leading to 2(P₂O₅) molecules. This indicates that implanted P ions substituted Zn sites in the ZnO layer. In photoluminescence spectroscopy, the P-related peaks observed at energies ranging between 3.1 and 3.5 eV originated from (A⁰, X) emission, because of P_Zn-2V_Zn complexes acting as shallow acceptors. The acceptor level was observed to be 126.9 meV above the valence band edge. Observation of this P-related emission indicates that ion implantation results in acceptor levels in the P-doped ZnO layer. This suggests that the P₂O₅ bonds are responsible for the p-type activity of P-implanted ZnO.     

Comparison of ZnO thin films deposited by three different SILAR processes

ZnO thin films were deposited on amorphous glass substrates using successive ionic layer adsorption and reaction (SILAR). The employed baths were ammonium zincate, with NH₃ and NH₄OH as complex agents and ZnSO₄ and Zn(NO₃)₂ as precursor sources. The comparison between films deposited by three processes was studied by means of X-ray diffraction (XRD), optical absorption, and micro Raman. The band gap is between 3.14 and 3.30 eV. By μ-Raman spectroscopy, the principal vibration modes around 435 and were determined in all the films.     

N∶ZnO薄膜的受主性质研究

使用溶胶-凝胶法制备N∶ZnO薄膜,用X射线衍射仪(XRD)对晶体结构进行表征,用扫描电子显微镜(SEM)观察薄膜表面形貌,用荧光光谱仪测量低温(8K)及变温条件(8～200K)下的光致发光(PL)光谱。分析了各个发射峰的形成机理,通过薄膜缺陷态发光和受主能级的关联性,计算出了N作为受主所需电离能的大小在0.255～0.31eV范围内。研究结果为以后P型ZnO薄膜的制备和研究提供了依据。     

Effect of deposition power in fabrication of highly efficient CdS:O/CdTe thin film solar cell by the magnetron sputtering technique

Polycrystalline II–VI semiconductor materials such as oxygenated CdS have a wide and tunable band gap (≥2.5 eV) which plays an important role in increasing the light absorption capacity of CdTe absorber. In this study, the ultra-thin CdS:O and CdTe films were deposited by the sputtering technique and the optimum condition of deposition power is investigated. The prepared ultra-thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, X-ray photoelectron spectroscopy (XPS), UV–vis spectrometry, Hall Effect and current–voltage measurements techniques. The complete cell was then fabricated by the sputtering technique with a novel configuration of ‘glass/FTO/ZnO:Sn/CdS:O/CdTe/C:Cu/Ag’. To avoid the pin hole effect, the high resistive ZnO:Sn layer was deposited as a buffer layer in between the FTO and CdS:O films. It has been observed that the cell performance parameters are found to be varied with deposition power of CdO:S films and an overall conversion efficiency of 10.27% was achieved.     

溶胶-凝胶旋涂法制备In掺杂ZnO薄膜结构和光学性能的研究

采用溶胶-凝胶(sol-gel)旋涂法在常规玻璃衬底 上生长了In掺杂浓度分别为1at%、2at%、3at%、4at%、5at%的ZnO薄膜。借助X射线衍射仪(X RD)、扫描电子显微镜(SEM)、紫外- 可见分光光度计(UV-Vis)对样品的晶粒生长、结构以及光学性能进行表征。结果如下:所 制 备的薄膜均沿(002)方向择优生长,且随着In³⁺掺杂浓度增加 ,衍射峰的峰型及半高宽均呈 先降低后升高的趋势;In³⁺掺入后,ZnO薄膜晶粒由原来的六边形状发展成类似蠕虫 状,同 时粒径变小且大小不一;与本征样品相比,掺杂后的ZnO光透过率提高了10%,且吸收边向短 波长方向偏移,同时随着In³⁺的掺入,薄膜的光学带隙值从3.49 eV增加到3.80 eV。当In³⁺掺 杂浓度为4at%时,薄膜(002)峰的峰形最为尖锐、峰值最大,晶粒较为均匀、 晶格间距更小,光透过率最高,光学带隙值相对较大为3.77 eV。     

Growth of Heteroepitaxial ZnO Thin Films on GaN‐Buffered Al2O3 (0001) Substrates by Low‐Temperature Hydrothermal Synthesis at 90 °C

Heteroepitaxial ZnO films are successfully grown on nondoped GaN‐buffered Al₂O₃ (0001) substrates in water at 90 °C using a two‐step process. In the first step, a discontinuous ZnO thin film (ca. 200 nm in thickness) consisting of hexagonal ZnO crystallites is grown in a solution containing Zn(NO₃)·6 H₂O and NH₄NO₃ at ca. pH 7.5 for 24 h. In the second step, a dense and continuous ZnO film (ca. 2.5 μm) is grown on the first ZnO thin film in a solution containing Zn(NO₃)·6 H₂O and sodium citrate at ca. pH 10.9 for 8 h. Scanning electron microscopy, X‐ray diffraction, UV‐vis absorption spectroscopy, photoluminescence spectroscopy, and Hall‐effect measurement are used to investigate the structural, optical, and electrical properties of the ZnO films. X‐ray diffraction analysis shows that ZnO is a monocrystalline wurtzite structure with an epitaxial orientation relationship of (0001)[11 0]_ZnO∥(0001)[11 0]_GaN. Optical transmission spectroscopy of the two‐step grown ZnO film shows a bandgap energy of 3.26 eV at room temperature. A room‐temperature photoluminescence spectrum of the ZnO film reveals only a main peak at ca. 380 nm without any significant defect‐related deep‐level emissions. The electrical property of ZnO film showed n‐type behavior with a carrier concentration of 3.5 × 10¹⁸ cm^–3 and a mobility of 10.3 cm² V^–1 s^–1.     

Nanostructured ZnO Films for Room Temperature Ammonia Sensing

Zinc oxide (ZnO) thin films have been deposited by a reactive dc magnetron sputtering technique onto a thoroughly cleaned glass substrate at room temperature. X-ray diffraction revealed that the deposited film was polycrystalline in nature. The field emission scanning electron micrograph (FE-SEM) showed the uniform formation of a rugby ball-shaped ZnO nanostructure. Energy dispersive x-ray analysis (EDX) confirmed that the film was stoichiometric and the direct band gap of the film, determined using UV–Vis spectroscopy, was 3.29 eV. The ZnO nanostructured film exhibited better sensing towards ammonia (NH₃) at room temperature (～30°C). The fabricated ZnO film based sensor was capable of detecting NH₃ at as low as 5 ppm, and its parameters, such as response, selectivity, stability, and response/recovery time, were also investigated.