Applications of in-situ and ex-situ spectroscopic ellipsometry （SE） are presented for the development of parametric expressions that define the real and imaginary parts （ε1, ε2） of the complex dielectric functio...Applications of in-situ and ex-situ spectroscopic ellipsometry （SE） are presented for the development of parametric expressions that define the real and imaginary parts （ε1, ε2） of the complex dielectric function spectra of thin film solar cell components. These spectra can then be utilized to analyze the structure of complete thin film solar cells. Optical and structural/compositional models of complete solar cells developed through least squares regression analysis of the SE data acquired for the complete cells enable simulations of external quantum efficiency （EQE） without the need for variable parameters. Such simulations can be compared directly with EQE measurements. From these comparisons, it becomes possible to understand in detail the origins of optical and electronic gains and losses in thin film photovoltaics （PC） technologies and, as a result, the underlying performance limitations. In fact, optical losses that occur when above-bandgap photons are not absorbed in the active layers can be distinguished from electronic losses when electron-hole pairs generated in the active layers are not collected. This overall methodology has been applied to copper indium-gallium diselenide （Culn1-xGaxSe2; CIGS） solar cells, a key commercialized thin film PV technology. CIGS solar cells with both standard thickness （〉2 μm） and thin （〈1 μm） absorber layers are studied by applying SE to obtain inputs for EQE simulations and enabling comparisons of simulated and measured EQE spectra. SE data analysis is challenging for CIGS material components and solar cells because of the need to develop an appropriate （ε1, ε2） database for the CIGS alloys and to extract absorber layer Ga profiles for accurate structural/compositional models. For cells with standard thickness absorbers, excellent agreement is found between the simulated and measured EQE, the latter under the assumption of 100% collection from the active layers, which include the CIGS bulk and CIGS/CdS heterojunction interface layers. For cells with thin absorbers, however, an observed difference between the simulated and measured EQE can be attributed to losses via carrier recombination within a- 0.15 μm thickness of CIGS adjacent to the Mo back contact. By introducing a carrier collection probability profile into the simulation, much closer agreement is obtained between the simulated and measured EQE. In addition to the single spot capability demonstrated in this study, ex-situ SE can be applied as well to generate high resolution maps of thin film multilayer structure, component layer properties and their profiles, as well as short-circuit current density predictions. Such mapping is possible due to the high measurement speed of 〈1 s per （ , 4） spectra achievable by the multichannel ellipsometer.展开更多
Bulk materials were synthesized by the Bridgman technique using the elements Cu, In and Se. These samples were characterized by Energy Dispersive Spectrometry (EDS) to determine the elemental composition, as well as b...Bulk materials were synthesized by the Bridgman technique using the elements Cu, In and Se. These samples were characterized by Energy Dispersive Spectrometry (EDS) to determine the elemental composition, as well as by X-ray diffraction for structure, hot point probe method for type of conductivity, Optical response (Photoconductivity) and Photoluminescence (PL) to determine the band gap value and Spectroscopic Ellipsometry to find energy levels above the gap in the band scheme at room-temperature. They show a nearly perfect stoechiometry and present a p-type conductivity. CuIn3Se5 either has a Stannite structure, an Ordered Defect Chalcopyrite structure (ODC), or an Ordered Vacancy Chalcopyrite structure (OVC). The gap energy obtained for the different samples was 1.23 eV. Energy levels above the gap in the band scheme were determinate by measuring the dielectric function at room temperature for energies lying between 1.5 and 5.5 eV. Many transitions were observed above the gap for different samples. Spectroscopic Ellipsometry gave evidence for the interpretation of the choice of gap values which were compatible with that obtained from solar spectrum.展开更多
Using Spectroscopic Ellipsometry (SE), the optical properties of Cu(In1−xGax)3Se5 bulk compounds, grown by the Bridgman method, were analyzed by varying x composition (0 ≤ x ≤ 1). Energy levels above the g...Using Spectroscopic Ellipsometry (SE), the optical properties of Cu(In1−xGax)3Se5 bulk compounds, grown by the Bridgman method, were analyzed by varying x composition (0 ≤ x ≤ 1). Energy levels above the gap in the band scheme were determined by measuring the complex dielectric function ?at room-temperature for energies between 1.5 and 5.5 eV using a variable angle of incidence ellipsometer. The transitions values E1, E2 and E3 were observed above the gap for different samples of Cu(In1−xGax)3Se5 alloy. When a gallium atom replaces an indium atom, one assumes globally that the levels related to selenium and copper are unchanged. Conversely, the levels corresponding to the conduction band are shifted towards higher energies. Thus, the gap increases as the composition of gallium increases. Spectroscopic Ellipsometry (SE) gave evidence for the interpretation of the choice of gap values which were compatible with that obtained from solar spectrum. Several other characterization methods like Energy Dispersive Spectrometry (EDS), hot point probe method, X-ray diffraction, Photoluminescence (PL), Optical response (Photoconductivity) were presented in this paper. The Cu(In1−xGax)3Se5 have an Ordered Vacancy Chalcopyrite-type structure with lattice constants varying as a function of the x composition. The band gap energy of Cu(In1−xGax)3Se5 compounds is found to vary from 1.23 eV to 1.85 eV as a function of x.展开更多
The Ag2O film, as-dcposited by direct-current magnetron reactive sputtering at a substrate temperature of 150 ℃, clearly shows a preferential orientation （111）, and is capable of lowering the threshold value of the...The Ag2O film, as-dcposited by direct-current magnetron reactive sputtering at a substrate temperature of 150 ℃, clearly shows a preferential orientation （111）, and is capable of lowering the threshold value of the thermal decomposition temperature to about 200℃, which is helpful to its application in optical and magneto-optical storage. This paper fits its optical constants in terms of a general oscillator model by using measured ellipsometric parameters. The fitted oscillator energy 2.487 eV is close to the optical direct interband transition energy value of the Ag2O film determined by Tauc equation; whereas, the fitted oscillator energy 4.249 eV is far from the fitted plasma oscillator energy 4.756 eV by single-oscillator energy. The photoluminescence spectrum centred at about 2.31 eV indicates a direct-energy gap photoluminescence mechanism of the Ag2O film.展开更多
The effect of a spherical shape on the measurement result of spectroscopic ellipsometry （SE） is analyzed, and a method to eliminate this effect is proposed. Based on the simulation result of the SE measurement on a ...The effect of a spherical shape on the measurement result of spectroscopic ellipsometry （SE） is analyzed, and a method to eliminate this effect is proposed. Based on the simulation result of the SE measurement on a silicon sphere by ray tracking, we find that the sphere makes the parallel incident beam of the SE be divergent after reflection, and the measurement error of the SE caused by this phenomenon is explained by the mixed polarization theory. By settling an aperture in front of the detector of the SE, we can almost eliminate the error. For the silicon sphere with a diameter of 94 mm used in the Avogadro project, the thickness error of the oxide layer caused by the spherical shape can be reduced from 0.73 nm to 0.04 nm by using the proposed method. The principle of the method and the results of the experimental verification are presented.展开更多
Stoichiometric Ba（MnxTi（1-x）O3） （BMT） thin films with various values of x were deposited on Si（111） substrates by the sol-gel technique. The influence of Mn content on the optical properties was studied by spe...Stoichiometric Ba（MnxTi（1-x）O3） （BMT） thin films with various values of x were deposited on Si（111） substrates by the sol-gel technique. The influence of Mn content on the optical properties was studied by spectroscopic ellipsometry （SE） in the UV–Vis–NIR region. By fitting the measured ellipsometric parameter （Ψ and Δ） with a four-phase model （air/BMT＋voids/BMT/Si（111））, the key optical constants of the thin films have been obtained. It was found that the refractive index n and the extinction coefficient k increase with increasing Mn content due to the increase in the packing density. Furthermore, a strong dependence of the optical band gap Eg on Mn/Ti ratios in the deposited films was observed, and it was inferred that the energy level of conduction bands decreases with increasing Mn content.展开更多
A series of （103）-oriented aluminum-doped zinc oxide （AZO） films were deposited on glass substrates via direct- current pulse magnetron reactive sputtering at different O2-to-Ar gas flow ratios （GFRs）. The optic...A series of （103）-oriented aluminum-doped zinc oxide （AZO） films were deposited on glass substrates via direct- current pulse magnetron reactive sputtering at different O2-to-Ar gas flow ratios （GFRs）. The optical properties of the films were characterized using the fitted optical constants in the general oscillator model （which contains two Psemi-Tri oscillators） through the use of measured ellipsometric parameters. The refractive index dispersion data below the interband absorption edge were analyzed using a single-oscillator model. The fitted optical energy gap obtained using the single- oscillator model clearly shows a blue shift, followed by a red shift, as the GFR increases from 0.9/18 to 2.1/18. This shift can be attributed to the change in the free electron concentration of the film, which is closely related to the film stress. In addition, the fitted β value indicates that the AZO film falls under the ionic class. The pbotoluminescence spectrum indicates a photoluminescence mechanism of the direct and wide energy gap semiconductor.展开更多
With recently developed In N epitaxy via a controlling In bilayer, spectroscopic ellipsometry（SE） measurements had been carried out on the grown In N and the measured ellipsometric spectra were fitted with the Delta...With recently developed In N epitaxy via a controlling In bilayer, spectroscopic ellipsometry（SE） measurements had been carried out on the grown In N and the measured ellipsometric spectra were fitted with the Delta Psi2 software by using a suitable model and the dispersion rule. The thickness was measured by a scanning electron microscope（SEM）. Insight into the film quality of In N and the lattice constant were gained by X-ray diffraction（XRD）. By fitting the SE, the thickness of the In N film is consistent with that obtained by SEM cross-sectional thickness measurement. The optical bandgap of InN was put forward to be 1.05 e V, which conforms to the experimental results measured by the absorption spectrum and cathodoluminescence（CL）. The refractive index and the extinction coefficient of interest were represented for InN, which is useful to design optoelectronic devices.展开更多
We prepare Si x （ZrO 2 ） 100 x composite films using the co-sputtering method. The chemical structures of the films which are prepared under different conditions are analyzed with X-ray photoemission spectroscopy. T...We prepare Si x （ZrO 2 ） 100 x composite films using the co-sputtering method. The chemical structures of the films which are prepared under different conditions are analyzed with X-ray photoemission spectroscopy. Thermal treatment influences on optical property and resistance switching characteristics of these composite films are investigated by spectroscopic ellipsometry and semiconductor parameter ana- lyzer, respectively. With the proper Si-doped Si x （ZrO 2） 100 x interlayer, the Al/ Si x （ZrO 2 ） 100 x /Al device cell samples present very reliable and reproducible switching behaviors. It provides a feasible solution for easy multilevel storage and better fault tolerance in nonvolatile memory application.展开更多
基金supported by the Department of Energy and the National Science Foundation(NSF)under the F-PACE Program,Award Number DE-EE0005400supported by NSF Award EECS-1665172
文摘Applications of in-situ and ex-situ spectroscopic ellipsometry （SE） are presented for the development of parametric expressions that define the real and imaginary parts （ε1, ε2） of the complex dielectric function spectra of thin film solar cell components. These spectra can then be utilized to analyze the structure of complete thin film solar cells. Optical and structural/compositional models of complete solar cells developed through least squares regression analysis of the SE data acquired for the complete cells enable simulations of external quantum efficiency （EQE） without the need for variable parameters. Such simulations can be compared directly with EQE measurements. From these comparisons, it becomes possible to understand in detail the origins of optical and electronic gains and losses in thin film photovoltaics （PC） technologies and, as a result, the underlying performance limitations. In fact, optical losses that occur when above-bandgap photons are not absorbed in the active layers can be distinguished from electronic losses when electron-hole pairs generated in the active layers are not collected. This overall methodology has been applied to copper indium-gallium diselenide （Culn1-xGaxSe2; CIGS） solar cells, a key commercialized thin film PV technology. CIGS solar cells with both standard thickness （〉2 μm） and thin （〈1 μm） absorber layers are studied by applying SE to obtain inputs for EQE simulations and enabling comparisons of simulated and measured EQE spectra. SE data analysis is challenging for CIGS material components and solar cells because of the need to develop an appropriate （ε1, ε2） database for the CIGS alloys and to extract absorber layer Ga profiles for accurate structural/compositional models. For cells with standard thickness absorbers, excellent agreement is found between the simulated and measured EQE, the latter under the assumption of 100% collection from the active layers, which include the CIGS bulk and CIGS/CdS heterojunction interface layers. For cells with thin absorbers, however, an observed difference between the simulated and measured EQE can be attributed to losses via carrier recombination within a- 0.15 μm thickness of CIGS adjacent to the Mo back contact. By introducing a carrier collection probability profile into the simulation, much closer agreement is obtained between the simulated and measured EQE. In addition to the single spot capability demonstrated in this study, ex-situ SE can be applied as well to generate high resolution maps of thin film multilayer structure, component layer properties and their profiles, as well as short-circuit current density predictions. Such mapping is possible due to the high measurement speed of 〈1 s per （ , 4） spectra achievable by the multichannel ellipsometer.
文摘Bulk materials were synthesized by the Bridgman technique using the elements Cu, In and Se. These samples were characterized by Energy Dispersive Spectrometry (EDS) to determine the elemental composition, as well as by X-ray diffraction for structure, hot point probe method for type of conductivity, Optical response (Photoconductivity) and Photoluminescence (PL) to determine the band gap value and Spectroscopic Ellipsometry to find energy levels above the gap in the band scheme at room-temperature. They show a nearly perfect stoechiometry and present a p-type conductivity. CuIn3Se5 either has a Stannite structure, an Ordered Defect Chalcopyrite structure (ODC), or an Ordered Vacancy Chalcopyrite structure (OVC). The gap energy obtained for the different samples was 1.23 eV. Energy levels above the gap in the band scheme were determinate by measuring the dielectric function at room temperature for energies lying between 1.5 and 5.5 eV. Many transitions were observed above the gap for different samples. Spectroscopic Ellipsometry gave evidence for the interpretation of the choice of gap values which were compatible with that obtained from solar spectrum.
文摘Using Spectroscopic Ellipsometry (SE), the optical properties of Cu(In1−xGax)3Se5 bulk compounds, grown by the Bridgman method, were analyzed by varying x composition (0 ≤ x ≤ 1). Energy levels above the gap in the band scheme were determined by measuring the complex dielectric function ?at room-temperature for energies between 1.5 and 5.5 eV using a variable angle of incidence ellipsometer. The transitions values E1, E2 and E3 were observed above the gap for different samples of Cu(In1−xGax)3Se5 alloy. When a gallium atom replaces an indium atom, one assumes globally that the levels related to selenium and copper are unchanged. Conversely, the levels corresponding to the conduction band are shifted towards higher energies. Thus, the gap increases as the composition of gallium increases. Spectroscopic Ellipsometry (SE) gave evidence for the interpretation of the choice of gap values which were compatible with that obtained from solar spectrum. Several other characterization methods like Energy Dispersive Spectrometry (EDS), hot point probe method, X-ray diffraction, Photoluminescence (PL), Optical response (Photoconductivity) were presented in this paper. The Cu(In1−xGax)3Se5 have an Ordered Vacancy Chalcopyrite-type structure with lattice constants varying as a function of the x composition. The band gap energy of Cu(In1−xGax)3Se5 compounds is found to vary from 1.23 eV to 1.85 eV as a function of x.
基金supported by the National Natural Science Foundation of China (Grant No.60807001)Foundation of Henan Educational Committee (Grant No.2010A140017)
文摘The Ag2O film, as-dcposited by direct-current magnetron reactive sputtering at a substrate temperature of 150 ℃, clearly shows a preferential orientation （111）, and is capable of lowering the threshold value of the thermal decomposition temperature to about 200℃, which is helpful to its application in optical and magneto-optical storage. This paper fits its optical constants in terms of a general oscillator model by using measured ellipsometric parameters. The fitted oscillator energy 2.487 eV is close to the optical direct interband transition energy value of the Ag2O film determined by Tauc equation; whereas, the fitted oscillator energy 4.249 eV is far from the fitted plasma oscillator energy 4.756 eV by single-oscillator energy. The photoluminescence spectrum centred at about 2.31 eV indicates a direct-energy gap photoluminescence mechanism of the Ag2O film.
基金Project supported by the National Key Technology Research and Development Program of the Ministry of Science and Technology of China(Grant No.2006BAF06B06)the Tsinghua University Initiative Scientific Research Program,China(Grant No.2009THZ06057)
文摘The effect of a spherical shape on the measurement result of spectroscopic ellipsometry （SE） is analyzed, and a method to eliminate this effect is proposed. Based on the simulation result of the SE measurement on a silicon sphere by ray tracking, we find that the sphere makes the parallel incident beam of the SE be divergent after reflection, and the measurement error of the SE caused by this phenomenon is explained by the mixed polarization theory. By settling an aperture in front of the detector of the SE, we can almost eliminate the error. For the silicon sphere with a diameter of 94 mm used in the Avogadro project, the thickness error of the oxide layer caused by the spherical shape can be reduced from 0.73 nm to 0.04 nm by using the proposed method. The principle of the method and the results of the experimental verification are presented.
基金Project supported by the National Natural Science Foundation of China(Grant No.60976016)the Postdoctoral Science Foundation of China(Grant No.2012M511250)the Foundation Co-established by Henan Province and the Ministry of Henan University,China(Grant No.SBGJ090503)
文摘Stoichiometric Ba（MnxTi（1-x）O3） （BMT） thin films with various values of x were deposited on Si（111） substrates by the sol-gel technique. The influence of Mn content on the optical properties was studied by spectroscopic ellipsometry （SE） in the UV–Vis–NIR region. By fitting the measured ellipsometric parameter （Ψ and Δ） with a four-phase model （air/BMT＋voids/BMT/Si（111））, the key optical constants of the thin films have been obtained. It was found that the refractive index n and the extinction coefficient k increase with increasing Mn content due to the increase in the packing density. Furthermore, a strong dependence of the optical band gap Eg on Mn/Ti ratios in the deposited films was observed, and it was inferred that the energy level of conduction bands decreases with increasing Mn content.
基金Project supported by the National Natural Science Foundation of China(Grant No.60807001)the Foundation of Young Key Teachers from University of Henan Province,China(Grant No.2011GGJS-008)+1 种基金the Foundation of Graduate Education Support of Zhengzhou University,Chinathe Foundation of Graduate Innovation of Zhengzhou University,China(Grant No.12L00104)
文摘A series of （103）-oriented aluminum-doped zinc oxide （AZO） films were deposited on glass substrates via direct- current pulse magnetron reactive sputtering at different O2-to-Ar gas flow ratios （GFRs）. The optical properties of the films were characterized using the fitted optical constants in the general oscillator model （which contains two Psemi-Tri oscillators） through the use of measured ellipsometric parameters. The refractive index dispersion data below the interband absorption edge were analyzed using a single-oscillator model. The fitted optical energy gap obtained using the single- oscillator model clearly shows a blue shift, followed by a red shift, as the GFR increases from 0.9/18 to 2.1/18. This shift can be attributed to the change in the free electron concentration of the film, which is closely related to the film stress. In addition, the fitted β value indicates that the AZO film falls under the ionic class. The pbotoluminescence spectrum indicates a photoluminescence mechanism of the direct and wide energy gap semiconductor.
基金Project supported by the State Key Development Program for Basic Research of China (No. 2012CB619301)the National High Technology Research and Development Program of China (No. 2014AA032608)+1 种基金the National Natural Science Foundation of China (Nos. 11204254, 11404271)the Fundamental Research Funds for the Central Universities (Nos. 2012121014, 20720150027)
文摘With recently developed In N epitaxy via a controlling In bilayer, spectroscopic ellipsometry（SE） measurements had been carried out on the grown In N and the measured ellipsometric spectra were fitted with the Delta Psi2 software by using a suitable model and the dispersion rule. The thickness was measured by a scanning electron microscope（SEM）. Insight into the film quality of In N and the lattice constant were gained by X-ray diffraction（XRD）. By fitting the SE, the thickness of the In N film is consistent with that obtained by SEM cross-sectional thickness measurement. The optical bandgap of InN was put forward to be 1.05 e V, which conforms to the experimental results measured by the absorption spectrum and cathodoluminescence（CL）. The refractive index and the extinction coefficient of interest were represented for InN, which is useful to design optoelectronic devices.
基金supported by the National Nature Science Foundation of China (No. 60578047)the National "973" Program of China (Nos. 2009CB929201 and No.2010CB933703)
文摘We prepare Si x （ZrO 2 ） 100 x composite films using the co-sputtering method. The chemical structures of the films which are prepared under different conditions are analyzed with X-ray photoemission spectroscopy. Thermal treatment influences on optical property and resistance switching characteristics of these composite films are investigated by spectroscopic ellipsometry and semiconductor parameter ana- lyzer, respectively. With the proper Si-doped Si x （ZrO 2） 100 x interlayer, the Al/ Si x （ZrO 2 ） 100 x /Al device cell samples present very reliable and reproducible switching behaviors. It provides a feasible solution for easy multilevel storage and better fault tolerance in nonvolatile memory application.
