Stacked Elemental Layer Research Articles

Progress on Numerical Reactive Diffusion Modeling of CuInSe2 Phase Formation for Solar Cell Applications

Numerical modeling of chalcopyrite (CuInSe2) absorber layer formation by rapid thermal annealed stacked elemental layers provides a valuable tool to address the microscopic phase formation process, which significantly determines the absorber layer properties in solar cell applications. We present a one dimensional kinetic modeling tool describing the diffusive reaction kinetics for layers of partial miscible systems. The diffusion is described temperature dependent and by calculating the latent heat the results were compared with differential scanning calorimetry measurement curves. Applying the numerical simulation to elemental layers of Cu, In and Se, first binary compounds are observed. With the presented progress in the model the absorber can completely react to CuInSe2, after sufficient intermixing of the elements. The results show a good agreement with experimental data with regard to the temperature range of the reactions taking place.

Growth of polycrystalline indium aluminum nitride thin films on silicon (111) substrates

Polycrystalline indium aluminum nitride (In, Al) N films were synthesized on silicon substrates using a stacked elemental layers (SEL) technique. Indium nitride and aluminum layers were deposited on Si (111) substrates through RF magnetron sputtering of indium target in Ar–N2 at 100°C and aluminum target in Ar atmosphere at 300 °C respectively. The deposited layers were annealed at 100 °C, 200 °C and 400 °C for four hours in a three zone ceramic furnace under nitrogen environment. The samples were characterized using an X-ray Diffractometer (XRD), Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray Spectrometer (EDX) and Atomic Force Microscope (AFM). XRD results indicated the formation of InN, AlInN and AlN phases which exhibited variations in the width and intensities with increase of the annealing temperature. Williamson–Hall (W–H) analysis of the diffraction peaks was carried out to estimate the structural parameters such as crystallite size, lattice strain, deformation stress and strain energy density. The FESEM results showed an increase in the grain size whereas the EDX analysis indicated a decrease in the aluminum contents with increase of the annealing temperature. The AFM measurements revealed a decrease in the surface roughness by increasing the annealing temperature from 100–200°C, however, the roughness was found to increase at 400°C.

Synthesis, characterization, and electronic structure of few-layer MoSe2 granular films

Few-layer MoSe2 granular films were prepared using rapid thermal processing (RTP) of stacked elemental layers (SELs) deposited using electron beam evaporation in the sequence of Mo/Se/Mo. RTP was carried out at various temperatures ranging from 550 to 750 °C, and durations ranging from 90 to 150 s. Morphology and microstructure of granular thin films were characterized by atomic force microscopy and scanning electron microscopy. Compositional and electronic structure analysis of the films were done by X-ray photoelectron, photoluminescence and Raman spectroscopy. The results confirmed the formation of four-layer MoSe2 granular thin films at 750 °C for 90 s. Density functional theory calculations showed that the direct gap at K is near degenerate with the calculated indirect band gap in the 4L structure. In addition to RTP, Raman laser annealing (RLA) was performed on SELs with various laser powers. Raman spectroscopy results reveal the local formation of MoSe2 with increasing laser energy.

Synthesis of aluminium indium nitride (AlInN) thin films by stacked elemental layers method

AlInN thin films were synthesized on Si substrates by using stacked elemental layers (SEL) technique. Three stacking sequence Al/InN, Al/InN/Al/InN and Al/InN/Al/InN/Al/InN were prepared on Si (1 0 0) substrates by reactive RF sputtering of In target in Ar-N 2 and DC sputtering of Al target in Ar atmosphere at room temperature. Annealing of the deposited stacks was carried out at 400 °C for 6 h in a three zone tube furnace. Structural properties of the annealed films were investigated using X-ray diffraction (XRD) whereas the surface analysis of the films was carried out using field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). XRD results show the formation of wurtzite AlInN thin films which become more obvious with increasing the stacked layers. FESEM analysis reveals drops-like polycrystalline films structure with randomly oriented grains whereas the AFM results show a decrease in the surface roughness with increasing stacking sequence. The formation of more prominent AlInN films with increase of stacking layers is attributed to a uniform interaction among the top and bottom Al and InN multilayers as a result of the annealing.

Crystal growth of Cu(In,Ga)Se2 film by RTP annealing of the stacked elemental layers formed by E-beam evaporation

Cu(In,Ga)Se2 (CIGS) thin films were successfully prepared by the application of a rapid thermal process to the stacked elemental layers (SEL), which were deposited by electron-beam (E-beam) evaporation method in the sequence of Cu/In/Ga/…/Cu/In/Ga. For the crystal growth of the CIGS absorber layer, an Se layer was deposited on top of the SEL precursors, and RTP annealing was carried out by a 2-step process at 200°C for 5min and at 550°C for 3min. The stoichiometry of the CIGS film with Cu/(In+Ga) and Ga/(In+Ga) atomic ratios of 0.90 and 0.26, respectively, was obtained with the optimum thickness ratio of the Cu/In and Ga precursor layers. In grown CIGS film, the suppression of Se loss during the annealing is very important. A subsidiary quartz box was used for sustaining maintaining the Se vapors during the selenization process in order to prevent Se loss. The experimental results show that the method is effective for preventing Se loss without the use of toxic H2Se gas or any other Se sources. The obtained CIGS film was homogeneous, and the surface morphology was dense with quite a large grain size of about 2μm.

Optical Properties and Surface Morphology of Zinc Telluride Thin Films Prepared by Stacked Elemental Layer Method

ZnTe thin films were prepared by Stacking of elemental (Zn and Te) layers (SEL) followed by inert gas annealing. The optical parameters were calculated from the transmission spectra. The bandgap of the annealed samples was found between 1.95 eV and 2.06 eV. The change in film thickness after annealing was observed using cross sectional SEM image of the annealed samples. The surface morphology of the annealed Te/Zn stack was also analyzed and observed as very smooth, compact and dense surface. The prepared film was Zn rich evidenced by EDAX. The observed result encourages in pursuing the SEL method for the preparation of compound semiconductor from II-VI group materials. DOI: http://dx.doi.org/10.5755/j01.ms.18.2.1908

Properties of Ag layered in Te/Cd stack prepared by stacked elemental layer method

Ag layered Te/Cd stack thin films (<1 µm thick) were prepared by the Stacked Elemental Layer (SEL) method. The XRD results revealed that the synthesized films had a polycrystalline nature. The synthesized films were preferentially oriented with (111) directions with a cubic phase. Structural studies were evidenced the formation of Ag related alloys at high annealing temperatures as a result of thermal diffusion in elemental stack. Optical and photo-resistivity studies revealed the influence of Ag on the CdTe lattice at high annealing temperatures. Surface morphology and the influence of Ag atoms on surface roughness are also presented.

Properties of Ag Doped CdTe Thin Film Prepared by Stacked Elemental Layer (SEL) Method

Thin films of elements (Cd,Te,Ag) were layered as a stack (Te/Cd/Te/Ag/Cd) for doping process with different Ag and Cd thickness by SEL method. The XRD results were depicted the presence of Cubic phase CdTe with (111) orientation along with Ag2Te, CdAgTe, AgTe phases. The peaks related to Ag atom at higher concentration evinced the presence of non-reacted Ag atoms on the surface with higher Ag concentration. The observed results showed the growth of CdTe crystals in (111) orientation with high Ag concentration. The AFM results of the annealed stack were clearly indicated the influence of Ag concentration in grain growth as well as surface roughness. Photo-resistivity studies of the annealed stacks also revealed the effect of Ag concentration in reducing the resistance with difference light sources. The observed results suggested that the SEL method could be used for effective doping of transition metals to achieve desired properties.

Synthesis and Properties of Sb Layered Te/Cd Stack Prepared by Elemental Stack Method

Sb layered Te/Cd thin films have been prepared by using Stacked Elemental Layer (SEL) method. The presence of mixed phases (CdTe and Sb2Te3) in the films was confirmed by the x-ray diffraction technique. The calculated structural parameters demonstrated the feasibility of Sb doping via SEL method. The topographical and electrical studies of the synthesized thin films depicted the influence of Sb on both surface morphology and conductivity. The values of conductivity of the annealed films were in between 2 x 10-3 and 175 x 10-2 Scm-2. A desired chemical composition of films was confirmed from spectrum shape analysis using energy dispersive x-ray.

Optimization of Thickness and Number of Layers for CdTe Films Deposited by Stacked Elemental Layers Method and Annealed in Different Environments

Optimization of Thickness and Number of Layers for CdTe Films Deposited by Stacked Elemental Layers Method and Annealed in Different Environments

Structural and Optical Properties of Zn Doped CdTe Thin Films by Stacked Elemental Layer Method

25% Zinc doped Cadmium Telluride thin films were prepared using Stacked Elemental Layer method. The structural studies were conducted by the X-Ray technique and the results were compared with standard data which confirmed the presence of mixed phases (CdTe, ZnTe and CdZnTe) in the stack annealed at 425°C. Transmittance spectra depicted the effect of Zn on the optical properties of CdTe thin film. The calculated band gaps from the transmittance spectra were lie between 1.42 and 1.51eV. Scanning Electron Microscope images elucidated the influence of Zn on surface morphology and the grain growth for CdTe thin films.

Low cost CuInSe 2 thin films production by stacked elemental layers process for large area fabrication of solar cell application

Low cost deposition of large area CuInSe 2 (CIS) thin films have been grown on Mo-coated glass substrate by simple and economic stacked elemental layer deposition technique in vacuum. The grown parameters such as concentration of Cu, In and Se elements have been optimized to achieve uniform thin film in vacuum chamber. The as-grown Cu/In/Se stacked layers have been annealed at 200 °C and 350 °C for 1 h in air ambient. The as-grown and annealed films have been further subjected to characterization by X-ray diffraction (XRD), optical absorption, atomic force microscopy (AFM) and I– V measurement techniques. XRD patterns revealed that as-grown Cu/In/Se stacked layers represent amorphous nature while annealed CIS film reproduces nano-polycrystalline nature with chalcopyrite structure. The optical band gap of annealed films increases with respect to air annealing which confirms the reduction of crystallite size. Surface morphology of as-grown Cu/In/Se stacked layers and annealed CIS thin films have been confirmed by AFM images. The electrical measurements show enhancement of conductivity which is useful for solar cell application.

Formation of CuInSe2 absorber by rapid thermal processing of electron-beam evaporated stacked elemental layers

Copper indium diselenide (CuInSe2) film was formed using the rapid thermal process (RTP) of electron-beam (E-beam) evaporated Cu–In stacked elemental layers as an absorber layer for chalcopyrite solar cells. The E-beam evaporation method could accurately control the thickness of each elemental layer so that the chemical composition of Cu–In precursor could also be controlled by changing the thickness ratio of the Cu/In metal layer. The device-quality Cu-deficient CuInSe2 film was obtained when the thickness ratio of Cu/In was about 1/2.5. Otherwise, the RTP process time was also certified as one of the most important parameters of RTP when the temperature was over 550 °C. A single-phase CuInSe2 was successfully obtained after rapid thermal process under 580 °C for 3 min. Finally, the growth mechanism of CuInSe2 film during RTP process was also summarized.

Fabrication of Cu(In,Ga)Se2 Thin Film by Selenization of Stacked Elemental Layer with Solid Selenium

Cu(In,Ga)Se2 thin films were prepared using the classical two-step process approach. In the first step, the metallic precursors were deposited on the soda-lime glass substrates by electron-beam evaporation following the Cu/In/Ga... sequence. The selenization, called the second step, was produced in a rapid thermal processor. This process performed under nitrogen atmosphere of 200 Torr at 200°C for 5 minutes followed by 500°C for 3 minutes. The device quality of CIGS film, with the atomic ratios of Cu/(In+Ga) of 0.90 and Ga/(In+Ga) of 0.26, was obtained when the Cu/In/Ga metallic layer had thinness ratio of 900 Aå/600 Aå /200 Aå. The CIGS film with homogeneous and dense surface morphology with large grain size (~ 2 μm) was formed.

The influence of gallium on phase transitions during the crystallisation of thin film absorber materials Cu(In,Ga)(S,Se) 2 investigated by in-situ X-ray diffraction

Chalcopyrite based photovoltaic materials Cu(In xGa 1 − x )(S ySe 1 − y ) 2 (CIGSSe) are substituted in the cation and anion lattice to adopt the semiconductor bandgap to the terrestrial solar spectrum. In-situ X-ray diffraction (XRD) investigations on the crystallisation of thin film absorber materials Cu(In,Ga)(S,Se) 2 while annealing stacked elemental layers (SEL) show phase transitions proceeding during the chalcopyrite synthesis. Thin layers of metals with elemental ratio Cu:In:Ga = 3:2:1 are deposited onto Mo-coated polyimide foil by DC-magnetron sputtering. The metal precursor is covered with S and subsequently Se by thermal evaporation of the elements in chalcogen excess (S + Se) / (Cu + In + Ga) = 2.3. Investigated chalcogen ratios reach from pure Se to pure S. Crystalline phases formed during the annealing of SEL are qualitatively determined. The results are compared to conclusions drawn from previous experiments on Ga-free CuIn(S,Se) 2 absorbers. The presence of Ga and S influences significantly the time-scale and the temperatures of phase transitions, i.e. the sulfoselenisation of precursor phases Cu 16(In,Ga) 9 and Cu 9(Ga,In) 4 proceeds faster with increasing S and is shifted to higher temperatures as compared to Ga-free Cu 11In 9/Cu 16In 9.

Synthesis of Nano-Structured Sb&lt;SUB&gt;2&lt;/SUB&gt;Te&lt;SUB&gt;3&lt;/SUB&gt; Thin Films by Stacked Elemental Layer Method

Nanostructured Sb 2 Te 3 thin films were synthesized by stacking the elemental layer which is allowed to isochronal annealing at various temperatures in the presence of Ar atmosphere. X-ray Diffraction (XRD) results confirm the presence of dominated (015) and (107) oriented hexagonal phase at above 350 °C. The crystallite size of about 58 nm of the annealed film was calculated from the XRD spectra. The XRD result shows the growth of H (105) oriented Sb 2 Te 3 thin films at this temperature region. The transmission spectra indicate good optical behavior of the annealed stack. The observed bandgap was between 2 and 2.5 eV. The resistivity of the annealed stack reveals the semiconductor behavior and also low resistance. Field Emission Scanning Electron Microscope (FESEM) images show that the deposit was composed of nano pillar like structure with the size of about 70 nm and uniform film thickness. Atomic Force Microscope (AFM) images also depicted the presence of nano size particles in Sb 2 Te 3 thin film and uniform surface morphology with roughness of about 38 nm. The particle size of about 60 nm could also be observed from AFM analysis. From the observed results, it is suggested that the synthesis of nano structured Sb 2 Te 3 thin film could be produced by using the Stacked Elemental Layer (SEL) method.

Studies on morphological change and optical properties for various Zn concentrations in CdTe thin film prepared by stacked elemental layer method

Te/Cd/Zn stack was prepared using stacked elemental layer (SEL) method. XRD results showed the effect of Zn concentration on the growth of CdTe in their preferred orientations. Optical studies revealed a reduction in band gap from 1.35 to 1.42 eV as well as low transmittance for higher Zn concentration. Improved surface morphology was the evidence of effects of Zn concentration on micro structural damage and the grain growth. Significant change on particle size, grain size and porosity was attributed to the influence of Zn concentration presented in the stack. ImageJ software also used to identify the presence of nano size particles in the annealed stack. EDAX studies revealed the presence of desired compositions in the annealed stacks.

A 3.2% efficient Kesterite device from electrodeposited stacked elemental layers

An improved electrodeposition-annealing route for preparing films of the Kesterite Cu 2ZnSnS 4 (CZTS) for thin film solar cell absorber layers is demonstrated. The material is prepared by sequential electrodeposition of a metallic precursor stack in the order Cu/Sn/Cu/Zn and subsequent annealing of the stack in an atmosphere containing sulfur. The new precursor is demonstrably more uniform on both macro-and microscopic scales, and this translates to enhanced lateral uniformity of the photoresponse of the CZTS film. Photovoltaic devices were prepared from the films, with the best cell having an efficiency of 3.2%.

Synthesis and characterization of 10% Sb doped CdTe thin films by stacked elemental layer (SEL) method

Antimony doped CdTe thin films have been prepared by stacked elemental layer (SEL) method. The X-ray diffraction spectra have demonstrated that the structure of the annealed films are polycrystalline in nature and mixed CdTe and Sb 2Te 3 phases have been observed at high annealing temperature (500 °C). The increased texture coefficient has been observed for planes (311) and (220) rather than (111) plane of CdTe in annealed stack (Te/Cd/Sb). Transmission spectra have been recorded and the calculated band gap lies between 1.45 and 1.68 eV. A pronounced PL spectrum has been noticed at 532 nm and depicted the presence of nano size particles in annealed thin films.

Real-time Investigations on the Formation of CuIn(S,Se)2 while annealing precursors with varying sulfur content

AbstractCIS based chalcopyrite absorber materials are usually substituted in the cation and anion lattice to yield mixed pentanary crystals with the general composition Cu(In,Ga)(Se,S)2 to achieve an optimised adaptation of the semiconductor bandgap to the terrestrial solar spectrum. Real-time investigations during the annealing of stacked elemental layers (SEL) of sputtered metals Cu and In and evaporated chalcogens S and Se with varying ratios were performed by angle-dispersive time-resolved XRD (X-ray diffraction) measurements. After qualitative phase analysis the measured powder diagrams were quantitatively analysed by the Rietveld method, the phases formed determined and their reaction kinetics obtained. Ternary indium and copper sulfoselenides form by the sulfoselenisation of the intermetallic alloy yielding different educts for the chalcopyrite formation with varying sulfur content. For S/(S+Se) ≥ 0.5 the formation of the chalcopyrite CuIn(S,Se)2 is similar to the crystallisation path of CuInS2. With increasing amount of selenium (S/(S+Se) = 0.25) different ternary sulfoselenides contribute to the semiconductor formation. For small amounts of sulfur, i.e. S/(S+Se) ≤ 0.1, the chalcopyrite crystallisation proceeds comparable to the one observed for sulfur-free Cu-In-Se precursors. The formation of CuIn(S,Se)2 is accelerated and proceeds mainly after the peritectic decomposition of Cu(S,Se) to Cu2(S,Se). The sulfur content determines the crystallisation temperature of the semiconductor because Cu(S,Se) decomposes at higher temperatures with increasing sulfur. Upon heating S ↔ Se exchange reactions take place in the Cu-S-Se and Cu-In-S-Se system.