Effect of the oxygen partial pressure on the microstructure and optical properties of ZnO:Cu films

Cu-doped zinc oxide (ZnO:Cu) films were deposited on Si substrates using radio frequency reactive magnetron sputtering at different oxygen partial pressures. The effect of oxygen partial pressure on the microstructures and optical properties of ZnO:Cu thin films were systematically investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and fluorescence spectrophotometer. The results indicated that the grain orientation of the films was promoted by appropriate oxygen partial pressures. And with increasing oxygen partial pressure, the compressive stress of the films increased first and then decreased. The photoluminescence (PL) of the samples were measured at room temperature. A violet peak, two blue peaks and a green peak were observed from the PL spectra of the four samples. The origin of these emissions was discussed and the mechanism of violet emission of ZnO:Cu thin films were suggested.     

Growth and properties of ZnS thin films by sulfidation of sputter deposited Zn

ZnS thin films with the hexagonal structure have been produced by sulfurizing sputter deposited Zn in sulfur vapor for 1 h. These films have been analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), synchrotron radiation photoelectron spectroscopy (SR-PES), Auger electron spectroscopy (AES) and UV-VIS transmission spectra. It is found that at the sulfidation temperature (T_S) of 400 °C a little and partial Zn can be transformed to ZnS. At T_S = 500 °C, the total conversion of Zn in sulfur vapor can take place and form ZnS with a c-axis preferred orientation. The Zn-to-ZnS conversion is kinetically a reactive diffusion process. Also the ZnS thin film has much greater size of grains than the as-deposited Zn film, due to ZnS recrystallization and growth in sulfur vapor. Residual sulfur existing on the surface of ZnS grains leads to the poor optical transparency and great broadening of absorbing edge in the optical transmittance. However, ZnS thin film prepared by gradient sulfidation exhibits the improved optical transmittance, with a band-gap energy of 3.64 eV.     

Effect of oxygen pressure on the structural and optical properties of ZnO thin films on Si (111) by PLD

ZnO thin films were grown on Si (111) substrates by pulsed laser deposition (PLD) at various oxygen pressures in order to investigate the structural and optical properties of the films. The optical properties of the films were studied by photoluminescence spectra using a 325 nm He-Cd laser. The structural and morphological properties of the films were investigated by XRD and AFM measurements, respectively. The results suggest that films grown at 20 Pa and 50 Pa have excellent UV emission and high-quality crystallinity. The research of PL spectra indicates that UV emission is due to excitonic combination, the green band is due to the replacing of Zn in the crystal lattice for O and the blue band is due to the O vacancies.     

衬底温度对磁控溅射法制备ZnO薄膜结构及光学特性的影响

采用射频反应磁控溅射法在玻璃衬底上制备了具有c轴高择优取向的ZnO薄膜,利用X射线衍射仪、扫描探针显微镜及紫外分光光度计研究了生长温度对ZnO薄膜的结构及光学吸收和透射特性的影响.结果表明,合适的衬底温度有利于提高ZnO薄膜的结晶质量;薄膜在紫外区显示出较强的光吸收,在可见光区的平均透过率达到90%以上,且随着衬底温度的升高,薄膜的光学带隙减小、吸收边红移.采用量子限域模型对薄膜的光学带隙作了相应的理论计算,计算结果与实验值符合得较好.     

Effect of oxygen partial pressure on microstructural and optical properties of titanium oxide thin films prepared by pulsed laser deposition

Nanocrystalline titanium oxide (TiO₂) thin films were deposited on silicon (1 0 0) and quartz substrates at various oxygen partial pressures (1 × 10⁻⁵ to 3.5 × 10⁻¹ mbar) with a substrate temperature of 973 K by pulsed laser deposition. The microstructural and optical properties were characterized using Grazing incidence X-ray diffraction, atomic force microscopy, UV–visible spectroscopy and photoluminescence. The X-ray diffraction studies indicated the formation of mixed phases (anatase and rutile) at higher oxygen partial pressures (3.5 × 10⁻² to 3.5 × 10⁻¹ mbar) and strong rutile phase at lower oxygen partial pressures (1 × 10⁻⁵ to 3.5 × 10⁻³ mbar). The atomic force microscopy studies showed the dense and uniform distribution of nanocrystallites. The root mean square surface roughness of the films increased with increasing oxygen partial pressures. The UV–visible studies showed that the bandgap of the films increased from 3.20 eV to 3.60 eV with the increase of oxygen partial pressures. The refractive index was found to decrease from 2.73 to 2.06 (at 550 nm) as the oxygen partial pressure increased from 1.5 × 10⁻⁴ mbar to 3.5 × 10⁻¹ mbar. The photoluminescence peaks were fitted to Gaussian function and the bandgap was found to be in the range ∼3.28–3.40 eV for anatase and 2.98–3.13 eV for rutile phases with increasing oxygen partial pressure from 1 × 10⁻⁵ to 3.5 × 10⁻¹ mbar.     

Structural analysis of chemically deposited nanocrystalline PbS films

Nanocrystalline PbS films are deposited on glass substrates by chemical bath deposition technique at room temperature. The structural parameters of PbS nanoparticles are studied by X-ray line profile analysis using Williamson-Hall and modified Williamson-Hall plot. The values of average crystallite sizes are found to vary from 12 to 18 nm having very high dislocation density of the order of 10¹⁷ m⁻².     

氧分压对掺钼氧化铟透明导电薄膜光电性能的影响

采用射频磁控反应溅射法在k9玻璃衬底上制备了In2O3∶Mo(IMO)透明导电薄膜,分析了不同氧分压条件下IMO薄膜的晶体结构、化学成分及光电性能.结果表明:不同氧分压下制备的IMO薄膜具有不同晶粒的取向性;随着氧分压的增加,薄膜的载流子浓度、载流子迁移率先增加后减小;薄膜的电阻率呈现先增加再减少然后再增加的趋势.在可...     

Effect of annealing treatment on structural, electrical, and optical properties of Ga-doped ZnO thin films deposited by RF magnetron sputtering

The effect of annealing on structural, electrical, and optical properties of Ga-doped ZnO (GZO) films prepared by RF magnetron sputtering was investigated in air and nitrogen. GZO films are polycrystalline with a preferred 002 orientation. The resistivities of annealed films are larger than the as-deposited. The transmittance in the near IR region increases greatly and the optical band gap decreases after annealing. The photoluminescence spectra is composed of a near band edge emission and several deep level emissions (DLE) which are dominated by a blue emission. After annealing, these DLEs are enhanced evidently.     

Effect of base and oxygen partial pressures on the electrical and optical properties of indium molybdenum oxide thin films

Indium molybdenum oxide thin films were RF sputtered at room temperature on glass substrates with a reference base pressure of 7.5 × 10^− 4 Pa. The electrical and optical properties of the films were studied as a function of oxygen partial pressures (OPP) ranging from 1.5 × 10^− 3 Pa to 3.5 × 10^− 3 Pa. The obtained data show that the bulk resistivity of the films increased by about 4 orders of magnitude (from 7.9 × 10^− 3 to 7.6 × 10¹ Ω-cm) when the OPP increased from 1.5 × 10⁻³ to 3.5 × 10^− 3 Pa, and the carrier concentration decreased by about 4 orders (from 1.77 × 10²⁰ to 2.31 × 10¹⁶ cm^− 3). On the other hand, the average visible transmittance of 30.54% of the films (brown colour; OPP = 1.5 × 10^− 3 Pa) was increased with increasing OPP to a maximum of 80.47% (OPP = 3.5 × 10^− 3 Pa). The optical band gap calculated from the absorption edge of the transmittance spectra ranges from 3.77 to 3.88 eV. Further, the optical and electrical properties of the films differ from those deposited at similar conditions but with a base pressure lower than 7.5 × 10^− 4 Pa.     

Surface modification of yttria-stabilized-zirconia thin films under various oxygen partial pressures

This report discusses the structural and spectroscopic analysis of yttria-stabilized-zirconia (YSZ) thin films grown on Al₂O₃(0001) substrates. It is found that the changes of oxygen partial pressure during the growth are closely related to the surface chemical compositions and the surface crystal orientations of the thin films. The presence of oxygen partial pressure produces a polycrystalline structure on the thin film while a preferred orientation of crystal structures is formed under no oxygen partial pressure. Difficulty arises in identifying the structure of the thin films due to the broad characteristics of the x-ray diffraction (XRD) peaks; however, the XRD rocking scan suggests the existence of two lateral domain sizes. The chemical analysis of the thin films from x-ray photoelectron spectroscopy measurements indicates the enrichment of surface yttrium-oxide as the oxygen partial pressure increases. The detailed analysis of valence band spectra also suggests that the thin films undergo a surface structural phase transition, i.e., transforming from a single tetragonal structure to a mixed (cubic + monoclinic) structure. Furthermore, the optical data display the small increments of the band gap as the oxygen partial pressure increases, which reflects the presence of the structural phase transition of the thin films.     

Size-dependent optical and dielectric properties of nanocrystalline ZnS thin films synthesized via rf-magnetron sputtering technique

Nanocrystalline ZnS thin films have been synthesized by radio frequency magnetron sputtering technique on glass and Si substrates at a substrate temperature 300 K. X-ray diffraction and selected area electron diffraction studies confirmed the formation of nanocrystalline cubic phase of ZnS in the films, although the target material was hexagonal ZnS. The particle size, calculated from the XRD patterns of the thin films was found in the range 2.06-4.86 nm. TEM micrographs of the thin films revealed the manifestation of ZnS nanoparticles with sizes in the range 3.00-5.83 nm. UV-vis-NIR spectrophotometric measurements showed that the films were highly transparent (∼90%) in the wavelength range 400-2600 nm with a blue shift of the absorption edge. The direct allowed bandgaps have been calculated and they lie in the range 3.89-4.44 eV. The particle size, calculated from the shift of direct bandgap, due to quantum confinement effect lying in the range 3.23-5.60 nm, well support the TEM results. The room temperature photoluminescence spectra of the films showed two peaks centered around 315 and 450 nm. We assigned the first peak due to bandgap transitions while the latter was due to sulfur vacancy in the films. The composition analysis by energy dispersive X-rays also supported the existence of sulfur deficiency in the films. The dielectric property study showed high dielectric constant (85-100) at a higher frequency (>5 kHz).     

Preparation and properties of ZnO thin films deposited by sol-gel technique

Zinc oxide (ZnO) thin films were deposited on (100) Si substrates by sol-gel technique. Zinc acetate was used as the precursor material. The effect of different annealing atmospheres and annealing temperatures on composition, structural and optical properties of ZnO thin films was investigated by using Fourier transform infrared spectroscopy, X-ray diffraction, atomic force microscopy and photoluminescence (PL), respectively. At an annealing temperature of 400°C in N₂ for 2 h, dried gel films were propitious to undergo structural relaxation and grow ZnO grains. ZnO thin film annealed at 400°C in N₂ for 2 h exhibited the optimal structure and PL property, and the grain size and the lattice constants of the film were calculated (41.6 nm, a = 3.253 ? and c = 5.210 ?). Moreover, a green emission around 495 nm was observed in the PL spectra owing to the oxygen vacancies located at the surface of ZnO grains. With increasing annealing temperature, both the amount of the grown ZnO and the specific surface area of the grains decrease, which jointly weaken the green emission. Translated from Journal of Lanzhou University (Natural Science), 2006, 42(1): 67–71 [译自: 兰州大学学报 (自然科学版)]     

Electrical and thermal transport properties of electrically stressed Bi-Sb-Te nanocrystalline thin films

Nanoscale size effect is beneficial for enhancing thermoelectric figure-of-merit of Bi-Sb-Te compounds due to the decrease of thermal conductivity. Bi-Sb-Te nanocrystalline thin films prepared by sputtering at room temperature, in general, require a post-deposition treatment to improve their electrical transport properties by eliminating residual crystal defects. In this study we present an electric current stressing treatment to effectively eliminate crystal defects in sputtered Bi-Sb-Te films at low temperature. By maintaining a low thermal conductivity of 0.6-0.7 W/mK, the electrically stressed Bi-Sb-Te nanocrystalline films possess highly enhanced Hall mobility and moderately reduced carrier concentration as compared to the films thermally treated at the same temperature. Carrier concentration, mobility and Seebeck measurement results suggest that the change of electrical transport properties involves the elimination of Sb_Te antisite defects as supported by the observation of some Sb-rich precipitates in the thermally/electrically treated Bi-Sb-Te films. Besides, crystal defects are also suggested to be preferentially removed in the (00l)-oriented grains due to anisotropic diffusion and electrical transport properties in the electrically stressed Bi-Sb-Te films.     

Hardness of sputter deposited nanocrystalline Ni3Al thin films

Nanocrystalline thin films of nominal composition Ni-25 at.% Al have been sputter deposited from a target of the intermetallic compound Ni₃Al using different sputtering conditions. Increase in the pressure of sputtering gas resulted in a substantial reduction in the grain size of these nanocrystalline films and a consequent enhancement in their hardness. While films deposited onto heated substrates exhibited larger grain sizes as compared to those deposited on unheated substrates at the same sputtering pressure, the hardness of the former films was substantially higher. The reason for this enhanced hardness is the long-range chemical ordering in films deposited on heated substrates and the formation of L1₂-Ni₃Al, the thermodynamically stable phase for this composition.     

O2气流量对MOCVD法生长ZnO薄膜性质的影响

采用低压MOCVD方法,在(0001)Al2O3衬底上沉积了ZnO薄膜.研究了Ⅵ族源O2气流量的变化对薄膜结构、表面形貌及光致发光特性的影响.增加O2气流量,ZnO薄膜结晶质量有所降低,半高宽从0.20°展宽至0.30°,由单一c轴取向变成无取向薄膜.同时,生成的柱状晶粒平均尺寸减少,晶粒更加均匀,均方根粗糙度减小.PL谱分析表明随O2气流量加大,带边峰明显增强,深能级峰明显减弱,ZnO薄膜光学质量提高.这些事实说明在本实验条件下,采用低压MOCVD方法生长的ZnO薄膜在光致发光特性主要依赖于Zn、O组份配比,而不是薄膜的微观结构质量.     

Impact of thickness on vacuum deposited PbSe thin films

Lead Selenide thin films were prepared by vacuum evaporation technique with different thickness ranges from 50 to 200 nm on glass substrates. The structural studies revealed that the prepared films are strongly oriented on (2 0 0) plane with rock-salt crystal structure. The various structural parameters such as grain size (D), lattice constant (a), micro strain (ε) and dislocation density (δ) were calculated. The surface morphology of the films was also analyzed. The optical absorption of the films starts with visible region and obtained energy gap of the films lies between 1.5 and 1.9 eV. The room temperature Photoluminescence spectrum shows the emission peak at visible region (380-405 nm) and the blue shift was observed with decreasing the film thickness. The electrical mobility, resistivity, carrier concentration and mean free path (L) of the free carriers of the films were studied for all the samples and compared.     

热氧化法制备纳米ZnO薄膜及其发光特性的研究

用热氧化ZnS薄膜方法制备纳米ZnO薄膜．并用X射线衍射谱．光致发光谱表征和研究纳米ZnO薄膜结构特征及热氧化温度对薄膜质量的影响。X射线衍射结果表明纳米ZnO薄膜具有六角纤锌矿结构．且随热氧化温度升高．薄膜晶粒尺寸逐渐增大。光致发光谱是由紫外激子发光和与氧空位有关的深能级缺陷发光组成的．且随热氧化温度升高，激子发光峰发生红移．激子发光和深能级缺陷发光强度之比逐渐增大．在热氧化温度为800℃时，其比值为10。     

Characterization on pulsed laser deposited nanocrystalline ZnO thin films

Nanocrystalline zinc oxide thin films were deposited on glass and silicon substrates by using pulsed laser deposition at different laser energy densities (1.5, 2, and 3 J/cm²). The film thickness, surface roughness, composition, optical and structural properties of the deposited films were studied using an α-step surface profilometer, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), optical transmittance, and X-ray diffraction (XRD), respectively. The film thickness was calculated as 244 nm. AFM analysis shows that the root-mean-square roughness increases with increasing laser energy density. XPS analysis shows that the interaction of zinc with oxygen atoms is greatly increased at high laser energy density. In the optical transmittance spectra, a shift of the absorption edge towards higher wavelength region confirms that the optical band gap increases with an increase in laser energy density. The particle size of the deposited films was measured by XRD, it is found to be in the range from 7.87 to 11.81 nm. It reveals that the particle size increases with an increase in laser energy density.     

Optimization of the structural, microstructural and optical properties of nanostructured Cr:ZnSe films deposited by magnetron co-sputtering for mid-infrared applications

In order to obtain optimally adherent films having the highest mid-infrared photoluminescence efficiency, nanostructured Cr²⁺:ZnSe films were deposited at room temperature on various substrates by magnetron radiofrequency co-sputtering of a SiO₂ target covered by a given number of ZnSe and Cr chips, at different Argon pressures and radiofrequency powers. The deposition parameter effect on the compositional, structural, microstructural and optical properties of the films has been investigated using X-ray reflectivity and diffraction, optical transmission spectroscopy, transmission electron microscopy, and photoluminescence studies. The corresponding films are composed by highly textured cubic and hexagonal ZnSe phases and exhibit strong tensile in-plane residual stresses. The evolution of the tensile residual stress and porosity values are consistent with the optical properties of the layers, and in particular the evolutions of both optical gap and refractive index. The room temperature mid-infrared (2-3 μm) photoluminescence measurements under direct excitation (1850 nm) revealed that chromium has been incorporated in the Cr²⁺ active state, and the corresponding fluorescence efficiency for an optimized thin film is only two times smaller than the one of a Cr²⁺:ZnSe reference bulk single crystal.