Thermoelectric Properties of Ag-doped Mg<Subscript>2</Subscript>Ge Thin Films Prepared by Magnetron Sputtering

Silver doped p-type Mg₂Ge thin films were grown in situ at 773 K using magnetron co-sputtering from individual high-purity Mg and Ge targets. A sacrificial base layer of silver of various thicknesses from 4 nm to 20 nm was initially deposited onto the substrate to supply Ag atoms, which entered the growing Mg₂Ge films by thermal diffusion. The addition of silver during film growth led to increased grain size and surface microroughness. The carrier concentration increased from 1.9 × 10¹⁸ cm⁻³ for undoped films to 8.8 × 10¹⁸ cm⁻³ for the most heavily doped films, but it did not reach saturation. Measurements in the temperature range of T = 200–650 K showed a positive Seebeck coefficient for all the films, with maximum values at temperatures between 400 K and 500 K. The highest Seebeck coefficient of the undoped film was 400 μV K⁻¹, while it was 280 μV K⁻¹ for the most heavily doped film at ∼400 K. The electrical conductivity increased with silver doping by a factor of approximately 10. The temperature effects on power factors for the undoped and lightly doped films were very limited, while the effects for the heavily doped films were substantial. The power factor of the heavily doped films reached a non-optimum value of ∼10⁻⁵ W cm⁻¹ K⁻² at 700 K.     

Effect of pH on Structural and Electrical Properties of Electrodeposited Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> Thin Films

Bi₂Te₃ thin films were electrodeposited at various pH values of a bismuth nitrate and tellurium oxide plating solution. Enhancement in pH results in a decrease in grain size. Transmission electron microscopy reveals the transformation of the film morphology from dispersed nanoparticles to connected chain-like nanostructures of Bi₂Te₃ as pH is increased. Electrical characterization for samples deposited in the temperature range of 300 K to 425 K shows a fourfold increase in Seebeck coefficient, S, between its maximum and minimum value as the solution pH changes from 1 to 3.5. Such enhancement of S is attributed to the increased connectivity of the nanostructures at higher pH.     

Structural,Optical and Electrical Properties of Polycrystalline CuO Thin Films Prepared by Magnetron Sputtering

Cupric oxide thin films were deposited on silicon and sapphire substrates by reactive radio frequency magnetron sputtering at different substrate temperatures. The results showed that the CuO films were composed of different sizes of CuO nano-grains and the CuO films deposited on Si substrates showed a more dense and uniform surface than that deposited on Al₂O₃ substrates. It was noted that both the CuO films deposited on Si and Al₂O₃ substrates revealed only CuO related diffractions and the preferred orientation of the CuO films changed from (002) to (111) as the substrate temperature increased. Moreover, the carrier concentration was 1.141?×?10¹⁸ cm^?3 and the mobility was 0.401 cm²/v s at 450°C substrate temperature. The controllable electrical properties of the films can be achieved by the variation of crystal quality arising from the substrate temperature.     

Electrical and Structural Real-Time Changes in Thin Thermoelectric (Bi<Subscript>0.15</Subscript>Sb<Subscript>0.85</Subscript>)<Subscript>2</Subscript>Te<Subscript>3</Subscript> Films by Dynamic Thermal Treatment

A recent trend in thermoelectrics is miniaturization of generators or Peltier coolers using the broad spectrum of thin-film and nanotechnologies. Power supplies for energy self-sufficient micro and sensor systems are a wide application field for such generators. It is well known that thermal treatment of as-deposited p-type (Bi_0.15Sb_0.85)₂Te₃ films leads to enhancement of their power factors. Whereas up to now only the start (as-deposited) and the end (after annealing) film stages were investigated, herein for the first time, the dynamical changes of sputter-deposited film properties have been observed by real-time measurements. The electrical conductivity shows a distinct, irreversible increase during a thermal cycle of heating to about 320°C followed by cooling to room temperature. The interpretation of the Seebeck and Hall coefficients points to an enhancement in Hall mobility after annealing. In situ x-ray diffractometry shows the generation of an additional Te phase depending on temperature. This is also confirmed by energy-dispersive x-ray microanalysis and the corresponding mapping by scanning electron microscopy. It is presumed that the Te enrichment in a separate, locally well-defined phase is the reason for the improvement in the integral film transport properties.     

Transport Properties of CuInTe<Subscript>2</Subscript> Thin Films Obtained by the Electrochemical Route

CuInTe₂ (CIT) thin films were potentiostatically electrodeposited onto cadmium sulfide thin films coated on fluorine doped tin oxide (FTO) glass in an aqueous bath at 75°C by the standard three-electrode system at ??0.7 V and ??0.8 V, with respect to an Ag/AgCl reference electrode. The electrodeposited layers were heat treated at?～?80°C in air ambient for 60 min. X-ray diffraction pattern and Raman analysis confirmed the formation of chalcopyrite CIT thin films upon heat treatment. The optical band gap of heat treated CIT films was found to be?～?1.0 eV and 0.95 eV deposited at ??0.7 V and ??0.8 V, respectively. Compact and good adhesive growth of CIT layers onto CdS coated FTO substrates is confirmed by field emission scanning electron microscopy. The current density–voltage (J–V) and capacitance–voltage (C–V) measurement was studied to understand the electronic quality of material for development of CIT layers for solar cell applications. The current density was found to be increased by two orders of magnitude upon low-temperature heat treatment. The capacitance–voltage measurement showed sharp depletion and accumulation region. The built in potential was found to be ～?60 mV and 145 mV in the as-deposited samples, deposited at ??0.7 V and ??0.8 V, respectively, whereas upon heat treatment it shifted to 159 mV and 210 mV. The capacitance of the CIT films was found to be a function of applied bias and increased with increasing the bias voltage. The depletion width of the heat treated sample was found to be?～?20 nm and 200 nm for the sample deposited at ??0.7 V and ??0.8 V, respectively. Thus, the sample deposited at ??0.8 V shows optimum electronic properties and is found to be suitable for opto-electronic applications.     

磁控反应溅射制备的SnO2多晶薄膜及其特性

采用反应磁控溅射制备了高阻SnO2薄膜.利用X射线衍射、透射光谱、霍尔效应、暗电导温度关系等方法研究了退火对薄膜的结构、光学和电学性质的影响.发现在510℃退火1h后,SnO2薄膜从非晶态转变为四方相结构的多晶薄膜,光能隙在3.79 eV和3.92 eV之间,电阻率为8.5Ω·cm,电导激活能约为0.322 eV.研究结果表明,此方法制备的SnO2高阻膜适合作为过渡层应用于CdTe太阳电池中.     

Effect of Rapid Thermal Annealing on Sputtered CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> Thin Films

Calcium copper titanium oxide (CaCu₃Ti₄O₁₂, abbreviated to CCTO) films were deposited on Pt/Ti/SiO₂/Si substrates at room temperature (RT) by radiofrequency magnetron sputtering. As-deposited CCTO films were treated by rapid thermal annealing (RTA) at various temperatures and in various atmospheres. X-ray diffraction patterns and scanning electron microscope (SEM) images demonstrated that the crystalline structures and surface morphologies of CCTO thin films were sensitive to the annealing temperature and ambient atmosphere. Polycrystalline CCTO films could be obtained when the annealing temperature was 700°C in air, and the grain size increased signifi- cantly with annealing in O₂. The 0.8-μm CCTO thin film that was deposited at RT for 2 h and then annealed at 700°C in O₂ exhibited a high dielectric constant (ε′) of 410, a dielectric loss (tan δ) of 0.17 (at 10 kHz), and a leakage current density (J) of 1.28 × 10⁻⁵ A/cm² (at 25 kV/cm).     

Effect of Annealing Temperature on Flowerlike Cu<Subscript>3</Subscript>BiS<Subscript>3</Subscript> Thin Films Grown by Chemical Bath Deposition

For widespread application of thin-film photovoltaic solar cells, synthesis of inexpensive absorber material is essential. In this work, deposition of ternary Cu₃BiS₃ absorber material, which contains abundant and environmentally benign elements, was carried out on glass substrate. Flowerlike Cu₃BiS₃ thin films with nanoflakes as building block were formed on glass substrate by chemical bath deposition. These films were annealed at 573 K and 673 K in sulfur ambient for structural improvement. Their structure was characterized using Raman spectroscopy, as well as their surface morphological and optical properties. The x-ray diffraction profile of as-deposited Cu₃BiS₃ thin film revealed amorphous structure, which transformed to orthorhombic phase after annealing. The Raman spectrum exhibited a characteristic peak at 290 cm^?1. Scanning electron microscopy of as-deposited Cu₃BiS₃ film confirmed formation of nanoflowers with diameter of around 1052 nm. Wettability testing of as-deposited Cu₃BiS₃ thin film demonstrated hydrophobic nature, which became hydrophilic after annealing. The measured ultraviolet–visible (UV–Vis) absorption spectra of the Cu₃BiS₃ thin films gave an absorption coefficient of 10⁵ cm^?1 and direct optical bandgap of about 1.42 eV after annealing treatment. Based on all these results, such Cu₃BiS₃ material may have potential applications in the photovoltaic field as an absorber layer.     

退火处理对离子束溅射WO3-x薄膜结构和特性的影响

利用离子束溅射结合后退火处理的方法制备了WO_3-x(0≤x≤1)薄膜,系统研究了不同退火气氛、退火温度和退火时间等条件对WO_3-x薄膜的晶体结构以及电学、光学和电致变色特性的影响。研究发现,当退火温度超过WO3结晶温度后,特别是在湿氧气氛下,退火温度越高、退火时间越长,WO_3-x薄膜的结晶度越好,除WO3主晶相显著增强以外,还会陆续出现O29W10、O49W18和WO₂等缺氧相;在干氧条件下,更高的退火温度和更长的退火时间都有助于降低WO_3-x薄膜的电阻值,也都有助于WO_3-x薄膜可见光透过率的提升;WO_3-x薄膜电致变色器件在632.8 nm波长处的光学调制值达到了70%左右,表现出良好的电致变色特性。     

Effects of Nb Content on the Ferroelectric and Dielectric Properties of Nb/Nd-Co-doped Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> Thin Films

Nd/Nb-co-substituted Bi_3.15Nd_0.85Ti_3?x Nb _x O₁₂ (BNTN _x , x = 0.01, 0.03, 0.05 and 0.07) thin films were grown on Pt/Ti/SiO₂/Si (100) substrates by chemical solution deposition. The effects of Nb content on the micro-structural, dielectric, ferroelectric, leakage current and capacitive properties of the BNTN _x thin films were investigated. A low-concentration substitution with Nb ions in BNTN _x can greatly enhance its remanent polarization (2P _r) and reduce the coercive field (2E _c) compared with those of Bi₄Ti₃O₁₂ (BIT) thin film. The highest 2P _r (71.4 μC/cm²) was observed in the BNTN_0.03 thin film when the 2E _c was 202 kV/cm. Leakage currents of all the films were on the order of 10^?6 to 10^?5 A/cm², and the BNTN_0.03 thin film has a minimum leakage current (2.1 × 10^?6 A/cm²) under the high electric field (267 kV/cm). Besides, the C–V curve of the BNTN_0.03 thin film is the most symmetrical, and the maximum tunability (21.0%) was also observed in this film. The BNTN_0.03 thin film shows the largest dielectric constant and the lowest dielectric loss and its maximum Curie temperature is 410 ± 5°C.     

射频磁控溅射法沉积非晶InGaZnO薄膜及真空退火对其性能的影响

采用RF磁控溅射法在石英玻璃上制备了InGaZnO薄膜,并对薄膜进行了真空退火实验,探讨了沉积过程中氧气流量及真空退火温度对薄膜的光学性质和电学性质的影响及其机理。测试结果表明薄膜的光透过率随氧气流的增加而增大,且当氧气流大于1cm3/min时,薄膜呈现出不导电性,在通入的氧气流为0.5cm3/min时迁移率达11.9cm2/(V·s)。经过真空退火后,氧气流小于1.5cm3/min时薄膜载流子浓度随退火温度的变化而变化;氧气流大于1.5cm3/min时样品由半绝缘性转变为半导电性。生长样品和退火样品均为n型半导体。     

Grain Size and Texture of Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> Thin Films Synthesized by Cosputtering Binary Sulfides and Annealing: Effects of Processing Conditions and Sodium

We investigate the synthesis of kesterite Cu₂ZnSnS₄ (CZTS) polycrystalline thin films using cosputtering from binary sulfide targets followed by annealing in sulfur vapor at 500°C to 650°C. The films are the kesterite CZTS phase as indicated by x-ray diffraction, Raman scattering, and optical absorption measurements. The films exhibit (112) fiber texture and preferred low-angle and Σ3 grain boundary populations which have been demonstrated to reduce recombination in Cu(In,Ga)Se₂ and CdTe films. The grain growth kinetics are investigated as functions of temperature and the addition of Na. Significantly, lateral grain sizes above 1 μm are demonstrated for samples grown on Na-free glass, demonstrating the feasibility for CZTS growth on substrates other than soda lime glass.     

Vapor Annealing as a Post-Processing Technique to Control Carrier Concentrations of Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> Thin Films

This article demonstrates that carrier concentrations in bismuth telluride films can be controlled through annealing in controlled vapor pressures of tellurium. For the bismuth telluride source with a small excess of tellurium, all the films reached a steady state carrier concentration of 4 × 10¹⁹ carriers/cm³ with Seebeck coefficients of −170 μV K⁻¹. For temperatures below 300°C and for film thicknesses of 0.4 μm or less, the rate-limiting step in reaching a steady state for the carrier concentration appeared to be the mass transport of tellurium through the gas phase. At higher temperatures, with the resulting higher pressures of tellurium or for thicker films, it was expected that mass transport through the solid would become rate limiting. The mobility also changed with annealing, but at a rate different from that of the carrier concentration, perhaps as a consequence of the non-equilibrium concentration of defects trapped in the films studied by the low temperature synthesis approach.     

Electrical Properties of Ca<Subscript>9</Subscript>ZnLi(PO<Subscript>4</Subscript>)<Subscript>7</Subscript> Ceramics Prepared by Reactive Pressureless Sintering

Well-crystallized Ca₉ZnLi(PO₄)₇ ceramics were prepared by reactive pressureless sintering at atmospheric pressure. The single-phase Ca₉ZnLi(PO₄)₇ ceramics were confirmed by x-ray diffraction (XRD). The dielectric and electrical properties were investigated over a wide frequency range (1 Hz to 1 MHz) by complex impedance spectroscopy at different temperatures between 25°C and 600°C. A dielectric anomaly was observed at 440°C, which might be related to the phase transition. The impedance Cole–Cole plot was used to analyze the results of complex impedance measurements, revealing that the electrical properties depend strongly on frequency and temperature. Two relaxation dispersions of the electrical parameters were found and analyzed in terms of bulk and grain-boundary ionic transfer processes. The slope of the alternating-current (AC) conductivity over a wide range of temperatures provides activation energies from 0.48 eV to 1.69 eV. These results suggest that the conduction process is of the mixed type.     

Growth of Epitaxial (110) 0.7Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-0.3PbTiO<Subscript>3</Subscript> Thin Films on r-Plane Sapphire Substrates by RF Magnetron Sputtering

The role of substrate temperature and substrate surface geometry in determining the crystal structure and crystallinity of 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ (PMN-PT) thin films grown on r-plane sapphire substrates is examined. A 30-nm-thick amorphous PMN-PT seed layer deposited at 250°C and subjected to rapid thermal annealing at 850°C results in the formation of an epitaxial (110) perovskite PMN-PT growth template that can be used for subsequent growth of single-crystal (110) perovskite PMN-PT films at elevated temperature. The data show that single-crystal perovskite is promoted when the films nucleate with the \( \langle \overline{1} 11 \rangle \) PMN-PT direction parallel to the \( \langle 0\bar{2}21 \rangle \) Al₂O₃ direction.     

溅射功率对Co-ZnO薄膜结构和光电性能的影响

以氧化锌陶瓷靶和金属钴靶为靶材,利用磁控共溅射方法制备钴掺杂氧化锌(Co-ZnO)薄膜。研究了溅射功率对薄膜的结构、光学和电学性能的影响。结果表明:薄膜具有类似于ZnO的六方纤锌矿结构,并沿C轴择优生长;作用在Co靶上的溅射功率对Co-ZnO薄膜的结构和光电性能有一定的影响。在其他条件不变的情况下,当Co靶上的溅射功率设置为10 W时,样品的结晶质量、表面形貌、光透过率、光致发光以及导电性能综合评价最优。     

Electronic and Optical Modeling of Solar Cell Compounds CuGaSe<Subscript>2</Subscript> and CuInSe<Subscript>2</Subscript>

We present dielectric-function-related optical properties such as absorption coefficient, refractive index, and reflectivity of the semiconducting chalcopyrites CuGaSe₂ and CuInSe₂. The optical properties were calculated in the framework of density functional theory (DFT) using linear combination of atomic orbitals (LCAO) and full-potential linearized augmented plane wave (FP-LAPW) methods. The calculated spectral dependence of complex dielectric functions is interpreted in terms of interband transitions within energy bands of both chalcopyrites; for example, the lowest energy peak in the e₂ (w) \varepsilon_{2} (\omega ) spectra for CuGaSe₂ corresponds to interband transitions from Ga/Se-4p → Ga-4s while that for CuInSe₂ emerges as due to transition between Se-4p → In-5s bands. The calculated dielectric constant, e₁ (0) \varepsilon_{1} (0) , for CuInSe₂ is higher than that of CuGaSe₂. The electronic structure of both compounds is reasonably interpreted by the LCAO (DFT) method. The optical properties computed using the FP-LAPW model (with scissor correction) are close to the spectroscopic ellipsometry data available in the literature.     

氩氧比与退火温度对磁控溅射VO2薄膜结构与电学性能的影响

采用反应直流磁控溅射法,通过调控溅射过程中的氩氧比,在石英玻璃衬底上制备了氧化钒薄膜,研究了溅射气氛及后处理条件对其微结构与电学性能的影响.经450和500℃退火,薄膜中易形成VO2,而550℃退火时薄膜中会形成大量非4价的钒氧化物.薄膜在较高温度500℃下退火时结晶度增加,但薄膜颗粒之间的间隙更为明显,导致电阻率显著提高;同时其电阻率-温度曲线的热滞回线宽度较窄,在加热过程中相转变温度较高.当氩氧比中氧含量增加时,沉积的VO2薄膜中生成了少量非4价的钒氧化物.结果表明,反应磁控溅射法制备的氧化钒薄膜的微结构、电阻率、相变温度等特性与氩氧比和后退火温度密切相关.     

磁控溅射法在LiNbO3衬底上制备ZnO薄膜及性能研究

采用磁控溅射法在(001)LiNbO3衬底上制备了ZnO薄膜,并对其进行了退火处理.利用X射线衍射仪(XRD)、紫外一可见光谱仪和光致发光谱(PL)对ZnO薄膜的结构和光学性能进行了分析.结果表明,ZnO薄膜具有(002)的择优取向,退火后ZnO薄膜的(002)衍射峰的强度增强,半高宽减小,(002)峰向高角度方向移动.退火后样品可见光透过率增加,光学带隙发生红移.退火后的样品,紫外发光峰强度增强,可见光发光峰强度相对减弱.