Optical constants of DC sputtering derived ITO, TiO2 and TiO2:Nb thin films characterized by spectrophotometry and spectroscopic ellipsometry for

📝 Abstract

Thin films of inorganic materials as Tin-doped indium oxide, titanium oxide, Niobium doped titanium oxide, were deposited for comparison on glass and Polyethylene terephthalate (PET) substrates with a DC sputtering method. These thin films have been characterized by different techniques: Dektak Surface Profilometer, X-ray diffraction (XRD), SEM, (UV/Vis/NIR) spectrophotometer and spectroscopic ellipsometry (SE). The optical parameters of these films such as transmittance, reflectance, refractive index, extinction coefficient, energy gap obtained with different electronic transitions, real and imaginary ({\epsilon}_r,{\epsilon}_i) dielectric constants, were determined in the wavelengths range of (200 - 2200) nm. The results were compared with SE measurements in the ranges of (0.56- 6.19) eV by a new amorphous model with steps of 1 nm. SE measurements of optical constant have been examined and confirm the accuracy of the (UV/Vis/NIR) results. The optical properties indicate an excellent transmittance in the visible range of (400 - 800) nm. The average transmittance of films on glass is about (86%, 91%, 85%) for (ITO, TiO2, TiO2:Nb (NTO)) respectively and decreases to about (85%, 81%, 82%) for PET substrates. For all these materials the optical band gap for direct transition was (3.53, 3.3, 3.6) eV on glass substrates and on PET substrates using two methods (UV and SE). A comparison between optical constants and thickness of these ultrathin films observed gives an excellent agreement with the UV results. The deposited films were also analyzed by XRD and showed an amorphous structure. The structural morphology of these thin films has been investigated and compared.

💡 Analysis

Thin films of inorganic materials as Tin-doped indium oxide, titanium oxide, Niobium doped titanium oxide, were deposited for comparison on glass and Polyethylene terephthalate (PET) substrates with a DC sputtering method. These thin films have been characterized by different techniques: Dektak Surface Profilometer, X-ray diffraction (XRD), SEM, (UV/Vis/NIR) spectrophotometer and spectroscopic ellipsometry (SE). The optical parameters of these films such as transmittance, reflectance, refractive index, extinction coefficient, energy gap obtained with different electronic transitions, real and imaginary ({\epsilon}_r,{\epsilon}_i) dielectric constants, were determined in the wavelengths range of (200 - 2200) nm. The results were compared with SE measurements in the ranges of (0.56- 6.19) eV by a new amorphous model with steps of 1 nm. SE measurements of optical constant have been examined and confirm the accuracy of the (UV/Vis/NIR) results. The optical properties indicate an excellent transmittance in the visible range of (400 - 800) nm. The average transmittance of films on glass is about (86%, 91%, 85%) for (ITO, TiO2, TiO2:Nb (NTO)) respectively and decreases to about (85%, 81%, 82%) for PET substrates. For all these materials the optical band gap for direct transition was (3.53, 3.3, 3.6) eV on glass substrates and on PET substrates using two methods (UV and SE). A comparison between optical constants and thickness of these ultrathin films observed gives an excellent agreement with the UV results. The deposited films were also analyzed by XRD and showed an amorphous structure. The structural morphology of these thin films has been investigated and compared.

📄 Content

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Optical constants of DC sputtering derived ITO, TiO2 and TiO2:Nb thin films characterized by spectrophotometry and spectroscopic ellipsometry for optoelectronic devices aMohammed RASHEED, bRÉGIS BARILLÉ a,bMOLTECH-Anjou, Universitéd’Angers/UMR CNRS 6200, 2 Bd Lavoisier, 49045
Angers, France corresponding email: rasheed.mohammed40@yahoo.com

Abstract Thin films of inorganic materials as Tin-doped indium oxide, titanium oxide, Niobium doped titanium oxide, were deposited for comparison on glass and Polyethylene terephthalate (PET) substrates with a DC sputtering method. These thin films have been characterized by different techniques: Dektak Surface Profilometer, X-ray diffraction (XRD), SEM, (UV/Vis/NIR) spectrophotometer and spectroscopic ellipsometry (SE).
The optical parameters of these films such as transmittance, reflectance, refractive index, extinction coefficient, energy gap obtained with different electronic transitions, real and imaginary (
,
) dielectric constants, were determined in the wavelengths range of (200 - 2200) nm. The results were compared with SE measurements in the ranges of (0.56- 6.19) eV by a new amorphous model with steps of 1 nm. SE measurements of optical constant have been examined and confirm the accuracy of the (UV/Vis/NIR) results. The optical properties indicate an excellent transmittance in the visible range of (400 - 800) nm. The average transmittance of films on glass is about (86%, 91%, 85%) for (ITO, TiO2, TiO2:Nb (NTO)) respectively and decreases to about (85%, 81%, 82%) for PET substrates. For all these materials the optical band gap for direct transition was (3.53, 3.3, 3.6) eV on glass substrates and on PET substrates using two methods (UV and SE). A comparison between optical constants and thickness of these ultrathin films observed gives an excellent agreement with the UV results. The deposited films were also analyzed by XRD and showed an amorphous structure. The structural morphology of these thin films has been investigated and compared. Keywords nanostructure, DC sputtering deposition, Transparent conductive oxides (TCOs), SEM, spectrophotometry, spectroscopic ellipsometry.

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Introduction ITO, TiO2 and TiO2:Nb (NTO) have been used as transparent electrodes in many optoelectronic devices such as: Dye synthesized solar cells (DSSC) [1, 2, 3], organic emitting diode and devices (OLEDs) [4, 5, 6], liquid crystal display (LCDs) [7, 8]. In addition, these films have wide range of well perspective applications using flexible substrates such as: optoelectronic devices [9, 10], flat panel displays [11, 12, 13], photovoltaic devices; DSSC [14, 15, 16, 17, 18, 19], organic solar cells [20, 21, 22], organic light emitting diode [23, 24, 25], gas sensors [26, 27], light emitting transistor [28], photocatalytic [29, 30], electrochromic [31, 32], perovskite solar cells [33, 34], microelectronic devices [35], and thin film transistor [36, 37]. Transparent thin films are usually fabricated by using different techniques, such as: sol-gel (spin coating) [38, 39], spray pyrolysis [40, 41, 42], reactive magnetron sputtering [43, 44, 45], chemical vapor deposition (LPCVD) [46, 47, 48], pulse laser deposition (PLD) [4, 49, 50], and RF magnetron sputtering [51, 52] etc. Researchers have an increasing interest in using DC sputtering technique to prepare transparent thin films with lower sputter voltage and obtain thin film at room temperature, in this way there is no increasing of substrate temperature. Flexible organic Polyethylene terephthalate (PET) has been chosen in this study as substrate because it has many advantages such as low cost, temperature stability, chemical and moisture resistance and durability. PET has a lowest price compare with other flexible plastic substrates as polyimide and glass. It matches deposition conditions for thin films solar cells (temperature, degassing, etc.) and the melting temperature degree of PET of about 250 – 260 ºC. Nevertheless, most of the thin films deposited on plastic substrate (PET) at room temperature deposition such as dc sputtering technique to prevent the PET substrates from damage due to the poor thermal ability of plastic substrates. PET is unsupported and a semi-crystalline thermo-plastic polyester derived from polyethylene terephthalate. Its excellent wear resistance, low coefficient of friction, high flexural modulus, and superior dimensional stability make it a versatile material for designing mechanical and electro- mechanical parts. The deposition conditions such as sputter power and pressure played an important role in film properties. The high quality of films on PET substrates gives the possibility as alternative substrates to replace the standard glasses. The electrical and optical properties of target-substrate are strongly depended on the deposition condition rate.
However, a very accurate control o

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