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Dependence of optical properties of thermal evaporated lead telluride films upon substrate temperature
Abstracts
parameter nonlinear curve fit method was used to determine the refractive index, absorption coefficient, and thickness of these films. The experimental result indicates the partially oxidized materials inside the films which reduce the transmittance of the films could be oxygen backfilled into a deposition chamber during the evaporation process to produce optical yttria thin films with a low absorption coefficient.
Determination of optical parameters of thin films from ellipsometric and photometric measurements A V Tikhonravov and M K Trubetskov, Moscow University,
Moscow 119899, USSR To determine optical parameters of thin films we use a conception of the solution of this problem as an inverse mathematical one. It means as follows. Let us choose some model. Within this model a thin film is described by the vector of optical parameters X. When solving the direct problem, with each vector of X-parameters we can determine both ellipsometric angles and reflectance and transmittance as functions of the incident light wavelength or of the angle of incidence. To solve the inverse problem of determination of thin film parameters using the experimental data some merit function is introduced. It compares the nearness of the measured and calculated data. The merit function depends on the vector of X-parameters. The concrete structure of this function is determined by the choice of the model of the thin film under investigation. The search of the optical parameters of the thin film is realized by minimization of the merit function F(X). Let us distinguish the main features of our approach to the determination of the thin film parameters. (1) The software worked out allows us to use different experimental data. The data obtained by several photometric and ellipsometric measurements can be used simultaneously. Depending on experimental data being at the disposal of a researcher the corresponding merit function is formed. To solve the inverse problem a hierarchy of thin film models containing that from the simplest homogeneous ones to the different models of inhomogeneous thin films is used. The intermediate position is occupied by models dealing with the system of several homogeneous thin films. The software worked out allows a model to be changed easily while solving the problem, the structure of the merit function and the algorithm of its calculation being changed automatically. The necessity of the use of different thin film models is caused by the conception of the choice of the model, being in accordance with the accuracy of the experimental data. (2) To solve the inverse problem based on inhomogeneous thin film models specific mathematical methods are used. They are based on several ideas of the optimal control theory such as Hamiltonian function and conjugated equations. The algorithms we used to solve the inverse problem allow us to take into account the available a priori information about the thin film under investigation. On the basis of the a priori information the choice of the proper model from the hierarchy as well as the setting of various limitations to the thin film parameters is possible. In the process of numerical determination of the thin film parameters we also use a conception of the regularization, an inverse problem formulated by A N Tikhonov. (3) The designed software makes it possible to carry out vari-
ous model investigations on the inverse problem solution. The aim of such investigations is to find out if it is possible to determine various thin film parameters on the basis of different experimental data with the given accuracy. For this purpose different thin film models can be used, for example, thin films with small absorption and thin films with different types of inhomogeneous optical parameters distribution. For the given model the experimental data typical for any possible ellipsometric or photometric measurements can be calculated, then the errors of any desired level can be introduced into it. Experimental data obtained in such a way allow the process of the inverse problem solution on any model from hierarchy to be simulated. Numerical experiments of such a kind supply a researcher with a lot of information on the possibility of determination of various physical parameters of a thin film, and allows him to choose the most productive experiment. (4) The software worked out has a developed system of multi level menu and database, it is supplied with comments written in English. It can be used on IBM-PC compatible computers.
Determination of optical constants of thin film in soft X-ray region Guo Yonghong and Fan Zengxiu, Shanghai Institute of Optics and Fine Mechanics, Academia Sinica, PO Box 800-211, Shanghai 201800, China The optical constants--the real and imaginary parts of the complex index of refraction--have been determined from the reflectance vs angle of incidence. A reflectometer was constituted. Using it, we measured the reflectance of thin film vs angle in several wavelengths: CuKa, TiKa, TiLa, SiKa, AIKa, MgKa, CKa. The nonlinear least-squares curve technique was used to determine the optical constants of the film from the measured data. The measured reflectance R is compared with the calculated reflectance, Ref, for all incidence angles and S is calculated :
S = Ei[wi(ln R i - l n Refi)2]. The reflectance is calculated from a film-on-substrate model, using the Fresnel reflection and transmission coefficients (modified to include the effects of surface roughness) ;
R e f = R e f (no, ko, n 1, kl, ao, a 1, d). The optical constants (n, k), the rms roughness (a), the film thickness (d)--the subscripts refer to film (1), substrate (0)--are varied so as to minimize S; the best-fit values of n, k, d, a, are those which correspond to the minimum of S. Results for C, W films are given in this work. The optical constants, the film thickness, and the rms toughness of film are determined.
Dependence of optical properties of thermal evaporated lead telluride films upon substrate temperature Feng Weiting, Shanghai Institute of Mechanical Engineering,
Department of Instrumentation, 516 Jun Gong Road, Shanghai 200093, China ; and Yen Yihsun, Shanghai Institute of Technical Physics, 420 Zhong Shan Bei Yi Road, Shanghai 200083, China New results on the optical properties of lead teiluride films are 1045
Abstracts
reported. Semitransmitting PbTe films were prepared by thermal evaporation. It is demonstrated in detail that the substrate temperature during deposition significantly influences the optical properties of PbTe films. The results indicate that PbTe films have the minimum absorption and maximum index of refraction when deposited at the substrate temperatures of 170 and 230°C, from a wavelength of 4-15 pm.
Invited paper Interface stress at thin film semiconductor heterostructures Taneo Nishino, Department of Electrical Engineering, Kobe Uni-
versity, Rikkoudai, Nada-ku, Kobe 65, Japan It is known that the interface properties at semiconductor heterostructures strongly affect the performance of optoelectronic devices constructed by semiconductor heterojunctions. Therefore it is very important to characterize these interface properties at semiconductor heterostructures. In this work the interface properties are discussed, particularly the interface stress at semiconductor heterostructures and report a new characterization method of such interface stress with the use of the luminescence due to deep-level impurities, particularly 3d transition-metal impurities involved in the materials. Here the results obtained with three technologically important semiconductor heterostructures are presented ; InGaPAs/GaAs, AIGaAs/GaAs and ZnSSe/GaAs grown on GaAs, using the Cr related luminescence at 0.839 eV in the GaAs substrate. It is known that the 3d transition-metal luminescence lines are very sharp compared with usual near-edge luminescence lines due to localization of d electrons, and very sensitive to perturbation such as strain field. We have applied these characteristics of transition-metal luminescence lines to probe the interface stress at semiconductor heterostructures. Three technologically important semiconductor heterostructures, InGaPAs/GaAs, A1GaAs/GaAs and ZnSSe/GaAs, have been investigated by this method, which were prepared by epitaxial growth on GaAs substrate doped with Cr impurities. The Cr-related luminescence spectra have been observed by exciting the GaAs substrate through the thin epitaxial layers with the 514.5 nm line of an Ar ion laser. The shift and splitting of the 0.839 eV Cr luminescence line have been measured and analyzed, which are caused by the existence of the interface stress due to lattice mismatching or differences in thermal expansion coefficients at the heterostructures. The biaxial interface stress acting on the GaAs substrate can be decomposed into both hydrostatic pressure and uniaxial stress components, and has been compared with the theoretical calculations of the latticemismatch and thermal stresses. As a result, the interface stress at InGaPAs/GaAs and A1GaAs/GaAs has been well explained by lattice-mismatch stress and the interface stress at ZnSSe/GaAs by thermal stress.
Interface structure of silicon and diamond film Ding Zhengming, Zhuang Zhicheng and Zhang Weidong, Shang-
hai Jiao Tong University, Shanghai 200030, China Diamond films produced by the CVD method have recently 1046
attracted great interest in the field of new material studies. In this paper, the interface structure between a single crystalline Si substrate and a diamond film which was deposited by EACVD on a pretreated Si wafer is studied by the method of XPS surface analysis and Laser Raman spectroscopy. In order to expose the interface, the diamond film can be gradually etched away by Ar ions. Based on the feature that different scattering angles of photoelectrons correspond to different detecting depths, the spectra with different scattering angles of 75, 45, 30° are acquired. In the 75 ° spectrum, the Si-2p peaks of SiO2 and Si appear at 103.4 and 99.4 eV, respectively. In the 45 ° spectrum, we found the Si-2p peak of Si decreasing, but an apparent rise appeared in 103-100 eV. This indicates a new structure has been generated. In the 30 ° spectrum, because the detecting depth comes to surface, the Si-2p peak of Si disappears, but a new peak at about 101.2 eV is found obviously. This indicates that the mixed structure of SiOx and SiCx (x < 2) is generated. The Si wafers on which no diamond film deposited are also analysed, only the Si-2p peak of SiO2 and Si can be found in the spectra. The Laser Raman spectra with different film thickness (d < 1/am, 1/am < d < 10 #m, d > 10 pm) are still analysed. For the thick films, the diamond structure peak at 1333 cm- 1is obviously large, but the peak of diamond-like, etc. at about 1550 c m - i is fairly weak. For the thin films, the diamond peak is quite weak, but the peak in the vicinity of 1550 cm 1 becomes wider and larger. This indicates the nondiamond carbon structure appearing. Therefore, we can reach a conclusion that a transition layer between the Si and film is generated in the growth process of diamond film. The first is a SiO2 layer produced on the pretreated Si substrate. The second is diamond-like and noncrystalline carbon structure layer. And the third is a diamond structure layer. Between SiO2 and C, there is a process of O-Si unsaturated bonds and gradually forming C-Si bonds. This transition layer is very important for diamond film deposition.
Study on interdiffusion of Fe-Ti compositionally modulated films by in situ X-ray diffraction Bai Haiyang, Chen Hong and Zhang Yun, Institute of Physics,
Academia Sinica, Beijing 100080, China; and Wang Wenkui, Institute of Physics, Academia Sinica, Beijing 100080, and International Centre for Materials, Academia Sinica, Shenyang 110015, China Interdiffusion of Fe-Ti compositionally modulated films in a solid state reaction has been investigated by the dynamic in situ X-ray diffraction technique. Decay of the X-ray modulation peak was measured at temperatures from 150 to 325°C and the peak's shift in its position was observed. The interdiffusion coefficients of Fe-Ti modulated films at different temperatures were calculated. Plots of the interdiffusion coefficient D vs the time t at different temperatures were obtained. According to the variation rate of D vs t, the activation energy Q relating to viscosity relaxation was calculated to be 8.3+0.2 kcal mole- i.
parameter nonlinear curve fit method was used to determine the refractive index, absorption coefficient, and thickness of these films. The experimental result indicates the partially oxidized materials inside the films which reduce the transmittance of the films could be oxygen backfilled into a deposition chamber during the evaporation process to produce optical yttria thin films with a low absorption coefficient.
Determination of optical parameters of thin films from ellipsometric and photometric measurements A V Tikhonravov and M K Trubetskov, Moscow University,
Moscow 119899, USSR To determine optical parameters of thin films we use a conception of the solution of this problem as an inverse mathematical one. It means as follows. Let us choose some model. Within this model a thin film is described by the vector of optical parameters X. When solving the direct problem, with each vector of X-parameters we can determine both ellipsometric angles and reflectance and transmittance as functions of the incident light wavelength or of the angle of incidence. To solve the inverse problem of determination of thin film parameters using the experimental data some merit function is introduced. It compares the nearness of the measured and calculated data. The merit function depends on the vector of X-parameters. The concrete structure of this function is determined by the choice of the model of the thin film under investigation. The search of the optical parameters of the thin film is realized by minimization of the merit function F(X). Let us distinguish the main features of our approach to the determination of the thin film parameters. (1) The software worked out allows us to use different experimental data. The data obtained by several photometric and ellipsometric measurements can be used simultaneously. Depending on experimental data being at the disposal of a researcher the corresponding merit function is formed. To solve the inverse problem a hierarchy of thin film models containing that from the simplest homogeneous ones to the different models of inhomogeneous thin films is used. The intermediate position is occupied by models dealing with the system of several homogeneous thin films. The software worked out allows a model to be changed easily while solving the problem, the structure of the merit function and the algorithm of its calculation being changed automatically. The necessity of the use of different thin film models is caused by the conception of the choice of the model, being in accordance with the accuracy of the experimental data. (2) To solve the inverse problem based on inhomogeneous thin film models specific mathematical methods are used. They are based on several ideas of the optimal control theory such as Hamiltonian function and conjugated equations. The algorithms we used to solve the inverse problem allow us to take into account the available a priori information about the thin film under investigation. On the basis of the a priori information the choice of the proper model from the hierarchy as well as the setting of various limitations to the thin film parameters is possible. In the process of numerical determination of the thin film parameters we also use a conception of the regularization, an inverse problem formulated by A N Tikhonov. (3) The designed software makes it possible to carry out vari-
ous model investigations on the inverse problem solution. The aim of such investigations is to find out if it is possible to determine various thin film parameters on the basis of different experimental data with the given accuracy. For this purpose different thin film models can be used, for example, thin films with small absorption and thin films with different types of inhomogeneous optical parameters distribution. For the given model the experimental data typical for any possible ellipsometric or photometric measurements can be calculated, then the errors of any desired level can be introduced into it. Experimental data obtained in such a way allow the process of the inverse problem solution on any model from hierarchy to be simulated. Numerical experiments of such a kind supply a researcher with a lot of information on the possibility of determination of various physical parameters of a thin film, and allows him to choose the most productive experiment. (4) The software worked out has a developed system of multi level menu and database, it is supplied with comments written in English. It can be used on IBM-PC compatible computers.
Determination of optical constants of thin film in soft X-ray region Guo Yonghong and Fan Zengxiu, Shanghai Institute of Optics and Fine Mechanics, Academia Sinica, PO Box 800-211, Shanghai 201800, China The optical constants--the real and imaginary parts of the complex index of refraction--have been determined from the reflectance vs angle of incidence. A reflectometer was constituted. Using it, we measured the reflectance of thin film vs angle in several wavelengths: CuKa, TiKa, TiLa, SiKa, AIKa, MgKa, CKa. The nonlinear least-squares curve technique was used to determine the optical constants of the film from the measured data. The measured reflectance R is compared with the calculated reflectance, Ref, for all incidence angles and S is calculated :
S = Ei[wi(ln R i - l n Refi)2]. The reflectance is calculated from a film-on-substrate model, using the Fresnel reflection and transmission coefficients (modified to include the effects of surface roughness) ;
R e f = R e f (no, ko, n 1, kl, ao, a 1, d). The optical constants (n, k), the rms roughness (a), the film thickness (d)--the subscripts refer to film (1), substrate (0)--are varied so as to minimize S; the best-fit values of n, k, d, a, are those which correspond to the minimum of S. Results for C, W films are given in this work. The optical constants, the film thickness, and the rms toughness of film are determined.
Dependence of optical properties of thermal evaporated lead telluride films upon substrate temperature Feng Weiting, Shanghai Institute of Mechanical Engineering,
Department of Instrumentation, 516 Jun Gong Road, Shanghai 200093, China ; and Yen Yihsun, Shanghai Institute of Technical Physics, 420 Zhong Shan Bei Yi Road, Shanghai 200083, China New results on the optical properties of lead teiluride films are 1045
Abstracts
reported. Semitransmitting PbTe films were prepared by thermal evaporation. It is demonstrated in detail that the substrate temperature during deposition significantly influences the optical properties of PbTe films. The results indicate that PbTe films have the minimum absorption and maximum index of refraction when deposited at the substrate temperatures of 170 and 230°C, from a wavelength of 4-15 pm.
Invited paper Interface stress at thin film semiconductor heterostructures Taneo Nishino, Department of Electrical Engineering, Kobe Uni-
versity, Rikkoudai, Nada-ku, Kobe 65, Japan It is known that the interface properties at semiconductor heterostructures strongly affect the performance of optoelectronic devices constructed by semiconductor heterojunctions. Therefore it is very important to characterize these interface properties at semiconductor heterostructures. In this work the interface properties are discussed, particularly the interface stress at semiconductor heterostructures and report a new characterization method of such interface stress with the use of the luminescence due to deep-level impurities, particularly 3d transition-metal impurities involved in the materials. Here the results obtained with three technologically important semiconductor heterostructures are presented ; InGaPAs/GaAs, AIGaAs/GaAs and ZnSSe/GaAs grown on GaAs, using the Cr related luminescence at 0.839 eV in the GaAs substrate. It is known that the 3d transition-metal luminescence lines are very sharp compared with usual near-edge luminescence lines due to localization of d electrons, and very sensitive to perturbation such as strain field. We have applied these characteristics of transition-metal luminescence lines to probe the interface stress at semiconductor heterostructures. Three technologically important semiconductor heterostructures, InGaPAs/GaAs, A1GaAs/GaAs and ZnSSe/GaAs, have been investigated by this method, which were prepared by epitaxial growth on GaAs substrate doped with Cr impurities. The Cr-related luminescence spectra have been observed by exciting the GaAs substrate through the thin epitaxial layers with the 514.5 nm line of an Ar ion laser. The shift and splitting of the 0.839 eV Cr luminescence line have been measured and analyzed, which are caused by the existence of the interface stress due to lattice mismatching or differences in thermal expansion coefficients at the heterostructures. The biaxial interface stress acting on the GaAs substrate can be decomposed into both hydrostatic pressure and uniaxial stress components, and has been compared with the theoretical calculations of the latticemismatch and thermal stresses. As a result, the interface stress at InGaPAs/GaAs and A1GaAs/GaAs has been well explained by lattice-mismatch stress and the interface stress at ZnSSe/GaAs by thermal stress.
Interface structure of silicon and diamond film Ding Zhengming, Zhuang Zhicheng and Zhang Weidong, Shang-
hai Jiao Tong University, Shanghai 200030, China Diamond films produced by the CVD method have recently 1046
attracted great interest in the field of new material studies. In this paper, the interface structure between a single crystalline Si substrate and a diamond film which was deposited by EACVD on a pretreated Si wafer is studied by the method of XPS surface analysis and Laser Raman spectroscopy. In order to expose the interface, the diamond film can be gradually etched away by Ar ions. Based on the feature that different scattering angles of photoelectrons correspond to different detecting depths, the spectra with different scattering angles of 75, 45, 30° are acquired. In the 75 ° spectrum, the Si-2p peaks of SiO2 and Si appear at 103.4 and 99.4 eV, respectively. In the 45 ° spectrum, we found the Si-2p peak of Si decreasing, but an apparent rise appeared in 103-100 eV. This indicates a new structure has been generated. In the 30 ° spectrum, because the detecting depth comes to surface, the Si-2p peak of Si disappears, but a new peak at about 101.2 eV is found obviously. This indicates that the mixed structure of SiOx and SiCx (x < 2) is generated. The Si wafers on which no diamond film deposited are also analysed, only the Si-2p peak of SiO2 and Si can be found in the spectra. The Laser Raman spectra with different film thickness (d < 1/am, 1/am < d < 10 #m, d > 10 pm) are still analysed. For the thick films, the diamond structure peak at 1333 cm- 1is obviously large, but the peak of diamond-like, etc. at about 1550 c m - i is fairly weak. For the thin films, the diamond peak is quite weak, but the peak in the vicinity of 1550 cm 1 becomes wider and larger. This indicates the nondiamond carbon structure appearing. Therefore, we can reach a conclusion that a transition layer between the Si and film is generated in the growth process of diamond film. The first is a SiO2 layer produced on the pretreated Si substrate. The second is diamond-like and noncrystalline carbon structure layer. And the third is a diamond structure layer. Between SiO2 and C, there is a process of O-Si unsaturated bonds and gradually forming C-Si bonds. This transition layer is very important for diamond film deposition.
Study on interdiffusion of Fe-Ti compositionally modulated films by in situ X-ray diffraction Bai Haiyang, Chen Hong and Zhang Yun, Institute of Physics,
Academia Sinica, Beijing 100080, China; and Wang Wenkui, Institute of Physics, Academia Sinica, Beijing 100080, and International Centre for Materials, Academia Sinica, Shenyang 110015, China Interdiffusion of Fe-Ti compositionally modulated films in a solid state reaction has been investigated by the dynamic in situ X-ray diffraction technique. Decay of the X-ray modulation peak was measured at temperatures from 150 to 325°C and the peak's shift in its position was observed. The interdiffusion coefficients of Fe-Ti modulated films at different temperatures were calculated. Plots of the interdiffusion coefficient D vs the time t at different temperatures were obtained. According to the variation rate of D vs t, the activation energy Q relating to viscosity relaxation was calculated to be 8.3+0.2 kcal mole- i.