Effect of deposition time on structural, optical and photoluminescence properties of Cd0.9Zn0.1S thin films by chemical bath deposition method

The present work investigates the effect of deposition times on the structural, optical and photoluminescence properties of Cd_0.9Zn_0.1S thin films deposited on glass substrate by chemical bath deposition method. The deposition time was varied from 30 to 90 min. The deposited films were uniform and adherent to the glass substrates and amorphous in nature. Structural, optical and photoluminescence properties of Cd_0.9Zn_0.1S thin films were studied through X-ray diffraction, energy dispersive X-ray, scanning electron microscopy, UV–Vis absorption, fourier transform infra red spectroscopy and photoluminescence spectroscopy. The average crystal size was increased from ~1.3 to 2.5 nm with increase in deposition times. The absorption of the films was increased and the absorption peak shifted to lower wavelength side when deposition time increases. The increased energy gap from 2.4 to 2.49 eV with deposition time was due to quantum size effect and better crystallization. The presence of functional groups and chemical bonding were confirmed by FTIR. PL spectra showed two well distinct and strong bands; blue band around 407–415 nm and green band around 537–541 nm due to size effect.     

Effect of high-temperature annealing on the optical and photoluminescence properties of nanocrystalline SiC films

The optical and photoluminescence (PL) properties of nanocrystalline 3C-SiC films and the effect of the boundary regions between the nanocrystals were studied for two sets of films: (a) films with 10-15 nm nanocrystal size obtained by direct ion deposition method and (b) similar films annealed in oxygen at 850-950 °C. It was shown that annealing of the nanocrystalline SiC films resulted in weaker absorption in a broad spectral range, and to the increase of the optical band gap from 1.8 to 2.2 eV. On the contrary, the edge PL bands in the UV range (2.2 to 2.4 eV) remained similar. In the IR range, three maxima absent in the as-grown films, appeared at 1.52 eV, 1.56 eV and 1.63 eV. Measurement of the intensity of PL maxima as a function of the excitation power showed a nonlinear dependence that was attributed to the onset of stimulated emission.     

Annealing effects on the structural and optical properties of growth ZnO thin films fabricated by pulsed laser deposition (PLD)

Annealed ZnO thin film at 300, 350, 400, 450 and 500 °C in air were deposited on glass substrate by using pulsed laser deposition. The effects of annealing temperature on the structural and optical properties of annealed ZnO thin films by grazing incident X-ray diffraction (GIXRD), transmittance spectra, and photoluminescence (PL) were investigated. The GIXRD reveal the presence of hexagonal wurtzite structure of ZnO with preferred orientation (002). The particle size is calculated using Debye–Scherrer equation and the average grain size were found to be in the range 5.22–10.61 ± 0.01 nm. The transmittance spectra demonstrate highly transparent nature of the films in visible region (>70 %). The calculation of optical band gap energy is found to be in the range 2.95–3.32 ± 0.01 eV. The PL spectra shows that the amorphous film gives a UV emission only and the annealed films produce UV, violet, blue and green emissions this indicates that the point defects increased as the amorphous film was annealed.     

Thickness dependent structural, electronic, and optical properties of Ge nanostructures

In the present paper, we have investigated structural, optical as well as electronic properties of electron beam evaporated Ge thin films having layer thicknesses ranging from ultra-thin (5 nm) to thick (200 nm). The Raman spectra show that all peaks are shifted towards lower wave number as compared to their bulk counterparts and are considered as a signature of nanostructure formation and quantum confinement effect. The Raman line exhibits transformation from nanocrystalline to microcrystalline phase with a reduction in blue shift of peak position with increase in Ge film thickness (>5 nm). Similarly, the optical absorption spectra corresponding to these films also show reduction in blue shift effect, although Ge 5 nm film shows the absorption behaviour quite different from higher thickness films. The corresponding band gap values obtained from absorption measurements are much larger than bulk Ge and are mainly attributed to the effect of quantum confinement as expected for small size particles calculated from GIXRD patterns. AFM data in each case are correlated and discussed with structural as well as optical results to support the effect of growth morphology on the above-mentioned observations. The results are further supported by photoelectron spectroscopy (PES), photoluminescence (PL) and resistivity measurements and are interpreted in terms of crystallinity and quantum confinement effect.     

Ammonia-free chemical bath deposition of nanocrystalline ZnS thin film buffer layer for solar cells

In this work, we prepared zinc sulfide thin films on glass substrates by ammonia-free chemical bath deposition method using thioacetamide as the sulfide source and Ethylene Diamine Tetra Acetic Acid disodium salt as the complexing agent in a solution of pH = 6.0. Thin films of ZnS with different thicknesses of 18–450 nm were prepared. The effect of film thickness and annealing temperature in atmospheric air, on optical properties, band gap energy and grain size of nanocrystals were studied. The X-ray diffraction analysis showed a cubic zinc blend structure and a diameter of about 2–5 nm for ZnS nanocrystals. The Fourier Transform Infrared spectrum of films revealed no peaks due to impurities. The as-deposited ZnS films had more than 70% transmittance in the visible region. The direct band gap of as-deposited films ranged from 3.68 to 3.78 eV and those of annealed films varied from 3.60 to 3.70 eV.     

Characterisation of size-controlled and red luminescent Ge nanocrystals in multilayered superlattice structure

Ge nanocrystals (Ge NCs) embedded in a multilayered superlattice structure have been fabricated and investigated. The presence of Ge NCs was confirmed by Raman scattering and X-ray diffraction measurements. The average size of Ge NCs was modulated by the sputtering time of Ge-rich layer and possible mechanisms have been proposed. The blue shift of optical absorption edge was observed with the decrease of nanocrystal size. The photoluminescence showed broad bands centred at ∼ 1.77 eV and ∼ 2.01 eV for 3.9 nm and 3.0 nm nanocrystals, respectively, which are consistent with the theoretical calculation in literature. The properties of shifted optical absorption and red luminescence are tentatively explained by quantum confinement in the Ge NCs.     

Influence of bias voltage on the optical and structural properties of nc-Si:H films grown by layer-by-layer (LBL) deposition technique

The effects of applying a positive bias of 25 to 100 V on the optical, structural and photoluminescence (PL) properties of hydrogenated nanocrystalline silicon (nc-Si:H) films produced by layer-by-layer (LBL) deposition technique has been studied. Optical characterization of the films has been obtained from UV-VIS-NIR spectroscopy measurements. Structural characterization has been performed using X-ray diffraction, micro-Raman spectroscopy and field emission scanning electron microscope (FESEM). PL spectroscopy technique has been used to investigate the PL properties of the films. In general, the films formed shows a mixed phase of silicon (Si) nanocrystallites embedded within an amorphous phase of the Si matrix. The crystalline volume fraction and grain size of the Si nanocrystallites have been shown to be strongly dependent on the applied bias voltage. High applied bias voltage enhances the growth rate of the films but reduces the refractive index and the optical energy gap of the films. Higher crystalline volume fraction of the films prepared at low bias voltages exhibits room temperature PL at around 1.8 eV (700 nm).     

Effects of annealing and deposition temperature on the structural and optical properties of AZO thin films

Al-doped ZnO (AZO) thin films were deposited on p- type Si(100) substrate by r.f magnetron sputtering at 200, 300 and 400 °C substrate temperatures. The deposited films were annealed in air atmosphere for 1 h at temperatures of 700, 800 and 900 °C. The deposition temperature and post-deposition annealing effects on structural and optical properties of the AZO samples were analyzed using X-ray diffraction, atomic force microscope and photoluminescence (PL). After annealing, the value of full width half maximum of the diffraction peaks was decreased as well as, the intensity of visible and strong UV PL emission peaks were increased with temperature. However, the deep-level emission related with zinc point defects was removed by annealing of the samples. Results revealed that all of the as-deposited and annealed AZO films have hexagonal structure along (002) direction and their crystallinity were improved with the increased deposition and post-growth annealing temperatures. In addition, the surface roughness and the particle size of the films were increased with increased deposition and annealing temperatures.     

Characterization and properties of GaN films deposited by middle-frequency magnetron sputtering with anode-layer ion source assistance

GaN films were deposited on Si (111) substrates at a high growth rate of 94 nm/min using middle-frequency (MF) magnetron sputtering method with anode-layer ion source assistance. XRD, TEM and PL experiments were used to investigate the structure and optical properties of the resulting films. GaN films produced under optimal conditions have an almost 1:1 N: Ga ratio. The O concentration decreased while the deposition rate increased with the increasing of bias voltages. Hexagonal polycrystal nature of the films was detected by the TEM and XRD measurements. Peaks located at 3.36 eV labeled as free-exciton were detected in the temperature dependence photoluminescence spectra. The binding energies of N 1s and Ga 3d were centered at 397.5 and 19.8 eV, respectively. The results show that the ion beam-assisted MF reactive magnetron sputtering method can be an encouraging method for deposition of polycrystalline GaN films at low temperatures.     

Characterization and properties of GaN films deposited by middle-frequency magnetron sputtering with anode-layer ion source assistance

GaN films were deposited on Si (111) substrates at a high growth rate of 94 nm/min using middle-frequency (MF) magnetron sputtering method with anode-layer ion source assistance. XRD, TEM and PL experiments were used to investigate the structure and optical properties of the resulting films. GaN films produced under optimal conditions have an almost 1:1 N: Ga ratio. The O concentration decreased while the deposition rate increased with the increasing of bias voltages. Hexagonal polycrystal nature of the films was detected by the TEM and XRD measurements. Peaks located at 3.36 eV labeled as free-exciton were detected in the temperature dependence photoluminescence spectra. The binding energies of N 1s and Ga 3d were centered at 397.5 and 19.8 eV, respectively. The results show that the ion beam-assisted MF reactive magnetron sputtering method can be an encouraging method for deposition of polycrystalline GaN films at low temperatures.     

Rare earth ions and Ge nanocrystals in SiO(2)

Experimental studies of Ge nanocrystals embedded in SiO(2) films doped with Er and Yb deposited by rf-magnetron sputtering are presented. Although inter-band photoluminescence (PL) from the Ge nanocrystals is not observed, it is nevertheless found that the presence of Ge nanocrystals is crucial for obtaining light emission from Er(3+) and Yb(3+). For both kinds of rare earth ions, the intensity of the related PL line has a maximum after heat treatment at 800?°C, and the PL excitation spectra for the two cases are very similar. This suggests that the presence and the structure of the nanocrystals are important for the efficiency of PL from Er(3+) and Yb(3+). Experiments performed with multilayer structures of Ge nanocrystals and SiO(2) show that the optically active rare earth ions are located in the SiO(2) layers, and not inside the Ge nanocrystals. The mechanism of energy transfer from Ge nanocrystals to the rare earth ions is found to be non-optical.     

[100]取向Al-Ti共掺杂ZnO薄膜的制备与光电性能研究

采用常压固相烧结法制备了Al-Ti共掺ZnO靶材, 采用射频磁控溅射技术及真空退火工艺, 在普通玻璃衬底上制备了具有[100]取向Al-Ti共掺杂ZnO薄膜(ZATO). 采用X射线衍射(XRD)、扫描电子显微镜(SEM)对ZATO薄膜的生长机理、显微结构、形貌进行了测试分析, 用四探针测试仪、紫外-可见分光光度计及荧光光谱仪对ZATO薄膜的光电性能进行了测试分析. 结果表明, ZATO薄膜经500℃保温3h退火后, 择优取向由(002)向(100)方向转变; 此时, 衍射谱上还观察到超点阵衍射线条. [100]取向ZATO薄膜的光学带隙从退火前的3.29降至2.86, 平均可见光透过率从90%降至70%, 表现为一般的透过性; 而电阻率则从1.89×10^-2Ω·cm降至1.25×10^-3Ω·cm, 呈现较好的导电性. 薄膜中均出现了380nm附近的带边发射(NBE)峰以及410、564nm的深能级发射峰, 且经500℃保温3h退火后, 这些峰的位置并未改变, 但峰强均明显减弱. 对上述实验机理进行了分析讨论.     

Characteristics of wide-gap hydrogenated amorphous SiC films prepared using electron cyclotron resonance CVD from acetylene

The deposition of hydrogenated amorphous silicon carbide (a-SiC:H) films from a mixture of silane, acetylene and hydrogen gas using the electron cyclotron resonance chemical vapor deposition (ECR-CVD) process is reported. The variation of the deposition and film characteristics such as the deposition rate, optical bandgap, photoluminescence and the infra-red (IR) absorption as a function of the hydrogen dilution is investigated. The deposition rate increases to a maximum value of 250 Å/min at a moderate hydrogen dilution ratio of 20 [hydrogen flow (sccm)/acetylene + silane flow (sccm)], and decreases in response to a further increase in the hydrogen dilution. There is no strong dependence of the optical bandgap of the hydrogen dilution within the dilution range investigated (10 to 60), and the optical bandgap calculated from the E₀₄ method varied marginally from 2.85 eV to 3.17 eV. The room temperature photoluminescence (PL) peak energy and intensity showed a prominent shift to a maximum value of 2.17 eV corresponding to maximum PL intensity at a moderate hydrogen dilution of 30. The PL intensity showed a strong dependence on the hydrogen dilution variation. IR absorption results show that films deposited at higher hydrogen dilution have more Si---C bonding.     

Ge掺杂ZnO薄膜光学特性的研究

采用射频磁控共溅射法在硅基片上沉积了Ge掺杂ZnO薄膜,所制备的样品具有强蓝光发射和弱黄光发射.通过分析Ge掺入量和退火温度对发光谱的影响,并与相同条件下所沉积的纯ZnO薄膜的发光特性进行比较,结果表明,蓝光发射可能与Ge杂质形成的施主能级有关,弱黄峰可能源于Ge替代Zn空位形成的杂质能级到价带的跃迁复合.     

Structural and optical properties of silicon nanocrystals grown by plasma-enhanced chemical vapor deposition

Silicon nanocrystals (Si-nc) embedded in SiO2 matrix have been prepared by high temperature thermal annealing (1000-1250 degrees C) of substoichiometric SiOx films deposited by plasma-enhanced chemical vapor deposition (PECVD). Different techniques have been used to examine the optical and structural properties of Si-nc. Transmission electron microscopy analysis shows the formation of nanocrystals whose sizes are dependent on annealing conditions and deposition parameters. The spectral positions of room temperature photoluminescence are systematically blue shifted with reduction in the size of Si-nc obtained by decreasing the annealing temperature or the Si content during the PECVD deposition. A similar trend has been found in optical absorption measurements. X-ray absorption fine structure measurements indicate the presence of an intermediate region between the Si-nc and the SiO2 matrix that participates in the light emission process. Theoretical observations reported here support these findings. All these efforts allow us to study the link between dimensionality, optical properties, and the local environment of Si-nc and the surrounding SiO2 matrix.     

Microstructure and dielectric functions of Ge nanocrystals embedded between amorphous Al2O3 films: study of confinement and disorder

Ge nanocrystals (6–9?nm) embedded between amorphous Al₂O₃ films were produced in a cluster beam deposition system. The microstructural evaluation and compressive stress experienced by the Ge nanocrystals due to the presence of an oxide layer, nanoparticle size distribution and their changes due to thermal annealing were studied by X-ray diffraction, HRTEM and Raman spectroscopy. Spectroscopic ellipsometry was used to measure the dielectric functions of the deposited films. A multilayer model based on the effective medium approximation was used to analyze the variation of percentage of defects and the extent of disorder with particle size of the nanocrystals. The correlation between the microstructural characteristics and optical properties was established by evaluating standard sum rules. Germanium nanocrystals show visible photo luminescence at room temperature around 3.0 and 2.8?eV. However, a peak shift towards lower energies with increasing particle size due to thermal annealing was not detected. The experimentally observed luminescence is presumably originated due to the presence of oxide-related defect centers at the interface between the germanium nanocrystals and the embedded oxide layers.     

Annealing effects of sapphire substrate on the structure and properties of ZnO films grown via pulsed laser deposition

The structure, morphology, and properties of ZnO films were examined in relation to an annealed sapphire substrate prepared via pulsed laser deposition. The annealing effects of the sapphire substrate on the ZnO films were studied via X-ray diffraction (XRD), atomic-force microscopy (AFM), and photoluminescence (PL) measurements. The XRD patterns and PL spectra results showed that the optical quality of the ZnO films was significantly affected by the annealing temperature of the sapphire substrate. The optimum annealing temperature of the sapphire substrate was 1400 degrees C. Atomically-flat-surface and high-density atomic steps were formed after annealing treatment, which were qualified to be good nucleation sites for ZnO film growth.     

沉淀法制备ZnS∶Cr纳米晶及其光学性能研究

以十二烷基苯磺酸钠和六偏磷酸钠作为分散剂,采用沉淀法制备了ZnS及不同掺杂浓度的ZnS∶Cr纳米晶。利用XRD和TEM对纳米晶物相和形貌进行了分析。结果表明,ZnS和ZnS∶Cr纳米晶均为立方闪锌矿结构,利用谢乐公式估算ZnS和ZnS∶Cr纳米晶平均粒径分别为2.1和2.2nm。TEM观察到纳米晶近似为球形,平均粒度为3nm左右,具有较好的单分散性且分布均匀。荧光光谱(PL)表明,纳米晶在420、440和495nm处有发射谱带,前两者被认为是S空位深陷阱发光,后者被认为是表面态或中心辐射复合发光。     

Structural and optical properties of CdS thin films grown by chemical bath deposition

Cubic cadmium sulphide (CdS) thin films with (111) preferential orientation were prepared by chemical bath deposition (CBD) technique, using the reaction between NH₄OH, CdSO₄ and CS(NH₂)₂. The films properties have been investigated as a function of bath temperature and deposition time. Structural properties of the obtained films were studied by X-ray diffraction analysis. The structural parameters such as crystallite size have been evaluated. The transmission spectra, recorded in the UV visible range reveal a relatively high transmission coefficient (70%) in the obtained films. The transmittance data analysis indicates that the optical band gap is closely related to the deposition conditions, a direct band gap ranging from 2.0 eV to 2.34 eV was deduced. The electrical characterization shows that CdS films' dark conductivities can be controlled either by the deposition time or the bath temperature.     

Synthesis of monodisperse CdS nanowires and their photovoltaic applications

Cadmium sulphide (CdS) nanowires with a monodisperse diameter of 3.6 nm and an aspect ratio of 10–170 were successfully synthesized using a simple and reproducible hot coordinating solvents method. The morphology and optical properties of the CdS nanocrystals were investigated using transmission electron microscopy (TEM), high-resolution TEM (HRTEM) ultraviolet–visible (UV–Vis) absorption spectroscopy and photoluminescence (PL) spectroscopy. It was found that using a long alkyl chain phosphonic acid-octadecylphosphonic acid (ODPA) causes a low diffusion rate and low reactivity which help to control the morphology of the nanocrystals. The timing of the injection process was also found to have critical effect on the morphology of the nanocrystals. Sharp peaks in both the UV–Vis absorption and PL spectra indicate that the size distribution of the diameter is nearly monodisperse. The photovoltaic properties of photovoltaic devices made with a blend of our nanowires and poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) were also investigated. Devices made with the nanowires were found to have double the I_sc observed in devices made with lower aspect ratio CdS nanorods. The possible reason of low photocurrent and high V_oc is maybe due to the presence of ligand in the nanocrystals.