Determination of optical properties of SnO2 films

Summary The optical properties of conductive transparent thin films of undoped SnO₂, prepared by using magnetron supttering, were studied by measuring the transmittance and the reflectance between λ=0.25 μm and λ=3μm. The extracted optical constants are interpreted to give values of a direct band gap of the order of 4 eV and of an indirect band gap of the order of 3 eV. Typical SnO₂ films transmit ≈85% of visible light, have sheet resistanceR _∂ (100÷800) Ω_∂ and resistivities of (2.4·10⁻³÷1.8·10⁻²) Ω cm.

---

Riassunto Mediante la misura dei valori di transmittanza e di riflettanza per lunghezze d'onda comprese fra 0.25 μm e 3 μm, sono state studiate le proprietà ottiche di film sottili (trasparenti e conduttivi) di SnO₂ non drogato, preparati mediante sputtering. Dai valori così ottenuti sono stati ricavati valori del gap diretto dell'ordine di 4 eV e di quello indiretto dell'ordine di 3 eV. Un film di SnO₂ presenta tipicamente valori della transmittanza intorno all'85%, per luce visibile,R _∂ intorno ai (100÷800) Ω_∂ e resistività fra 2.4·10⁻³ e 1.8·10⁻² Ω cm.

---

Резюме Пзмеряя величины пропускания и отражения в области длин волн между λ=0.25 мкм и λ=3 мкм, исследуются оптические свойства проводящих прозрачных тонких пленок нелегированного SnO₂, приготовленных с помощью напыления. Из полученных оптических постоянных извлекаются значения прямой щели, порядка 4 эВ, и непрямой щели, порядка 3 эВ. Типичные пленки SnO₂ пропускают ∼85% видимого света, имеют сопротивлениеR _∂ (100÷800) Ω_∂ и удельные сопротивления в области (2.4·10⁻³÷1.8·10⁻²) Ом·см.

     

Fabrication of Cu2ZnSn(SxSe1−x)4 thin film solar cell by single step sulfo-selenization of stacked metallic precursors

We have synthesized an efficient Cu₂ZnSn(S_xSe_1−x)₄ (CZTSSe) absorbers by using single-step rapid thermal sulfo-selenization process of sputtered stack metallic precursor (Zn/Sn/Cu) films. The structural and morphological studies confirm that the suitability of the rapid thermal sulfo-selenization process for the synthesis of a CZTSSe absorber without any secondary phases with large grains. The annealing atmosphere with a mixed-chalcogen source enhances the grain growth of the CZTSSe absorber as compared with pure Cu₂ZnSnS₄ (CZTS) and Cu₂ZnSnSe₄ (CZTSe) absorbers. The CZTSSe thin film solar cell shows the best conversion efficiency of ∼7%.     

Influence of substrate activation process on structural and optical properties of ZnS thin films

ZnS thin films were deposited on glass substrates by a chemical bath deposition method using a substrate activation process in which aluminum ions become “contaminants” that act as a nucleation center for active components within the deposition solution. The structure and morphology results demonstrate that the films have a ZnS sphalerite crystal structure with a particle size less than 15 nm, and the films consist of small homogeneous grains. The effects of the substrate activation process on the band gap energies and donor-acceptor pair luminescence process were also investigated. A green emission centered at 502 nm was produced due to donor-acceptor transitions from the aluminum acceptor to the ionized and substitution aluminum centers (Al³⁺).     

Many-body Green's function theory for the magnetic reorientation of thin ferromagnetic films

The field-induced reorientation of the magnetization of ferromagnetic films is treated within the framework of many-body Green's function theory by considering all components of the magnetization. We present a new method for the calculation of expectation values in terms of the eigenvalues and eigenvectors of the equations of motion matrix for the set of Green's functions. This formulation allows a straightforward extension of the monolayer case to thin films with many layers and for arbitrary spin and moreover provides a practicable procedure for numerical computation. The model Hamiltonian includes a Heisenberg term, an external magnetic field, a second-order uniaxial single-ion anisotropy, and the magnetic dipole-dipole coupling. We utilize the Tyablikov (RPA) decoupling for the exchange interaction terms and the Anderson-Callen decoupling for the anisotropy terms. The dipole coupling is treated in the mean-field approximation, a procedure which we demonstrate to be a sufficiently good approximation for realistic coupling strengths. We apply the new method to monolayers with spin and to multilayer systems with S=1. We compare some of our results to those where mean-field theory (MFT) is applied to all interactions, pointing out some significant differences. Received 19 June 2000 and Received in final form 2 August 2000     

有机分子束外延技术与研究进展

本介绍了超高真空分子束外延生长有机薄膜的技术及基研究进展,讨论了外延材料的纯化过程和杂质对外延薄膜的影响;从理论和实验观点评论了薄膜的生长性质和膜的有序结构。超高真空有机分子束外延技术是一种多用途的高技术,可以生长有机、无机、有机／无机混和的薄膜结构。这种薄膜结构是示来光学和电子器件有希望应用的新一类工程材料。     

TiO_2薄膜的硼掺杂对TiO_2/p~+-Si异质结器件电致发光的增强

利用磁控溅射在重掺硼硅(p+-Si)衬底上分别沉积TiO2薄膜和掺硼的TiO2(Ti O2∶B)薄膜,并经过氧气氛下600℃热处理,由此形成相应的TiO2/p+-Si和TiO2∶B/p+-Si异质结。与Ti O2/p+-Si异质结器件相比,TiO2∶B/p+-Si异质结器件的电致发光有明显的增强。分析认为:TiO2∶B薄膜经过热处理后,B原子进入TiO2晶格的间隙位,引入了额外的氧空位,而氧空位是TiO2/p+-Si异质结器件电致发光的发光中心,所以上述由B掺杂引起的氧空位浓度的增加是TiO2∶B/p+-Si异质结器件电致发光增强的原因。     

Ni/SnO_2复合薄膜的制备与光电性能

采用旋涂法将溶胶-凝胶法制备的Ni/Sn O2凝胶在玻璃基底上镀膜,得到了Ni/Sn O2复合薄膜,探讨了镍掺杂量、煅烧温度对薄膜结构和形貌的影响。通过X射线衍射、红外光谱、扫描电子显微镜等测试手段对Ni/Sn O2复合膜的结构和形貌进行表征。结果显示,500℃下煅烧的薄膜样品的结晶度较高,粒径小,颗粒分布均匀。用紫外-可见分光光度计和四探针电阻仪对其进行光学、电学性能测试,结果显示:适量的Ni掺杂可以提高Sn O2薄膜在近紫外光区的吸收,Ni/Sn O2薄膜在近紫外光区的吸收随着Ni2+掺杂摩尔分数从5%增加到10%而逐渐减小。当Ni2+掺杂摩尔分数为6%时,Ni/Sn O2复合薄膜的导电性能最好。     

Theoretical stability,thin film synthesis and transport properties of the Mon +1GaCn MAX phase

The phase stability of Mo_{n +1}GaC_n has been investigated using ab‐initio calculations. The results indicate stability for the Mo₂GaC phase only, with a formation enthalpy of –0.4 meV per atom. Subsequent thin film synthesis of Mo₂GaC was performed through magnetron sputtering from elemental targets onto Al₂O₃ [0001], 6H‐SiC [0001] and MgO [111] substrates within the temperature range of 500 °C and 750 °C. High structural quality films were obtained for synthesis on MgO [111] substrates at 590 ºC. Evaluation of transport properties showed a superconducting behavior with a critical temperature of approximately 7 K, reducing upon the application of an external magnetic field. The results point towards the first superconducting MAX phase in thin film form. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Back contact–absorber interface modification by inserting carbon intermediate layer and conversion efficiency improvement in Cu2ZnSn(S,Se)4 solar cell

Carbon layers have been employed as intermediate layers between Mo back contact and Cu₂ZnSn(S_1–xSe_x)₄(CZTSSe) absorber film prepared by sol–gel and post‐selenization method. Carbon layers with appropriate thickness can significantly inhibit the formation of MoSe₂ and voids at bottom region of the absorber, and therefore reduce the series resistance remarkably. The conversion efficiency can be boosted by the introducing of the carbon layer from 6.20% to 7.24% by enhancement in short current density, fill factor and open voltage in comparison to the reference sample without carbon layer. However, excess thickness of carbon layer will worse device performance due to the deteriorated absorber crystallinity. In addition, the time‐resolved photoluminescence analysis shows that inserting the carbon layer with suitable thickness does not introduce recombination and lower minority lifetime. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Effect of 60Co γ-irradiation on structural and optical properties of thin films of Ga10Se80Hg10

Thin films of Ga₁₀Se₈₀Hg₁₀ have been deposited onto a chemically cleaned Al₂O₃ substrates by thermal evaporation technique under vacuum. The investigated thin films are irradiated by ⁶⁰Co γ-rays in the dose range of 50–150 kGy. X-ray diffraction patterns of the investigated thin films confirm the preferred crystallite growth occurs in the tetragonal phase structure. It also shows, the average crystallite size increases after γ-exposure, which indicates the crystallinity of the material increases after γ-irradiation. These results were further supported by surface morphological analysis carried out by scanning electron microscope and atomic force microscope which also shows the crystallinity of the material increases with increasing the γ-irradiation dose. The optical transmission spectra of the thin films at normal incidence were investigated in the spectral range from 190 to 1100 nm. Using the transmission spectra, the optical constants like refractive index (n) and extinction coefficient (k) were calculated based on Swanepoel’s method. The optical band gap (E_g) was also estimated using Tauc’s extrapolation procedure. The optical analysis shows: the value of optical band gap of investigated thin films decreases and the corresponding absorption coefficient increases continuously with increasing dose of γ-irradiation.