Open Access
Add to BibSonomyAbstract
In this study, we investigated whether the optical and electrical properties of indium tin oxide (ITO) films are degraded under laser irradiation below their laser ablation threshold. While performing multi-pulse laser damage experiments on a single ITO film (4.7 ns, 1064 nm, 10 Hz), we examined the optical and electrical properties in situ. A decrease in reflectance was observed prior to laser damage initiation. However, under sub-damage threshold irradiation, conductivity and reflectance of the film were maintained without measurable degradation. This indicates that ITO films in optoelectronic devices may be operated below their lifetime laser damage threshold without noticeable performance degradation.
© 2017 Optical Society of America
1. Introduction
Transparent conducting films (TCFs) have been used extensively in the optoelectronic industry [1, 2]. Their development to date has mostly focused on the optimization of light transmission and electrical conductivity [3]. Recently, however, a need has emerged to increase the optical damage performance of transparent conducting films to support more powerful optoelectronic applications such as high repetition rate, high power lasers [4] and optically addressable light valves [5]. In these applications, an optoelectronic crystal is sandwiched by a pair of TCFs such as indium tin oxide (ITO); the films operate as electrodes to apply electric field to the crystal while remaining transparent to the incident laser beam. Thin optical films have lower damage thresholds than bulk optical components and often limit the operational power of these laser systems [6, 7]. Furthermore, ITO films are damaged upon laser irradiation at lower fluences compared to dielectric coatings due to free carrier absorption [8, 9]. Therefore, the survivability of ITO films is of great importance in achieving reliable and efficient operation of high-power optoelectronic systems.
In order to achieve optically robust TCFs that can withstand high incident laser powers, fluences can be reduced by increasing the total irradiated area (the beam can be spread over large area films) [10, 11], or the properties of films such as free carrier concentration and thickness can be optimized to decrease light absorption while maintaining low sheet resistances [9]. ITO is a promising material in these regards because it is easily deposited over large area substrates [3, 12] and its properties can be controlled by varying temperature, pressure, and gas composition during deposition [13–18] or through post-deposition annealing [19–22]. This tunability, however, also suggests that film properties such as electrical conductivity, optical absorption, or overall transparency may change during the operation of ITO-based devices due to laser-induced thermo-mechanical [9] or thermo-chemical [23] modifications. Such modifications may degrade device performance and lead to catastrophic failure.
A study of the lifetime degradation and damage behavior of ITO films under high-fluence laser irradiation is therefore very important. Some studies have investigated the physical characteristics of ITO films under ultra violet (UV) laser irradiation [23, 24]. The excimer lasers used in these studies (photon energy > 4.0 eV) are intrinsically opaque to ITO (bandgap: ~4 eV), resulting in a degradation of the films via inter-band absorption. However, in order to utilize ITO films as TCFs for high laser intensity applications, the transparent wavelength range of ITO films should be used. Some studies investigated damage induced by 1064 nm laser exposures, for which the photon energy is less than the bandgap of the film material. In these, laser damage was produced via free carrier absorption [9, 25]. In general, however, laser damage studies on ITO films have focused on high fluence regimes relevant to ablation processes during single-pulse irradiation. In this study, we focused on the lifetime degradation/damage behavior of the films upon multi-pulse irradiation below the lifetime laser damage threshold, which is more relevant to device operation. To this end, we performed multi-pulse laser damage experiments on a single ITO film using a nanosecond (ns), 1064 nm laser (1.16 eV) and examined the optical and electrical properties of the film under multi-pulse irradiation below its laser ablation threshold.
2. Experimental methods
2.1 ITO film samples
The ITO film was deposited using an LGA Thin Films RF sputtering system in an argon (Ar) atmosphere with a 10% ITO target. Two inch round fused silica substrates were cleaned by a sputter etch process that was performed for 2 minutes at 10 mTorr in Ar before the deposition. The chamber pressure was maintained at 15 mTorr with a power of 0.9 kW during the deposition of the roughly 200 nm thick film. The total deposition time was 29 minutes, corresponding to a deposition rate of ~1 Ȧ/s. No additional heating was carried out during or after the deposition. The carrier concentration (Ne), electron mobility, and sheet resistance of the film were measured as 2.0 × 1020 cm−3, 18.8 cm2/Vs, and 82 Ω/sq, respectively, using an Ecopia Hall effect system operated at room temperature.
2.2 Laser damage experiments
The ns laser system shown in Fig. 1(a) was used for all laser damage experiments. The FWHM pulse duration was 4.7 ns and the wavelength was 1064 nm. The laser pulse energy was controlled using a thin film polarizer and a half-wave plate. A single 200 nm thick ITO film, deposited on a 500 μm thick fused silica substrate, was examined during irradiation. Laser pulses were delivered to the film surface at a 0° angle of incidence through a single lens (focal length: 150 mm) under ambient conditions. The 1/e2 diameter of the Gaussian beam profile was measured as 165 μm using a beam profiler (Spiricon, SP620). For the single pulse laser damage experiments, a single laser pulse was applied at a pristine location on the film. For multiple pulse laser damage experiments, multiple pulses were applied at a single location with a repetition rate of 10 Hz. The power stability of the laser was measured to be ± 5% over extended use.
Fig. 1 (a) Schematics of nanosecond (ns) laser damage system integrated with in situ reflectance monitoring using co-incident beams with a pulsed 1064 nm pump laser (4.7 ns pulse width) and a 532 nm (green, continuous wave) probe laser. The electrical and optical properties of the ITO film were monitored while the film was exposed to ns laser irradiation. (b) Schematics of ITO channel structure for electric property measurements. (c) Microscope image from in situ camera. The green probe laser beam is displayed over a damage site produced by the ns laser pulse.
2.3 Damage characterizations
Optical micrographs and surface profiles were obtained using a 3D Laser Scanning Confocal Microscope (Keyence, VK-X100). In order to determine the electrical response of the film upon laser irradiation, we fabricated a 200 µm wide ITO channel structure from the ITO film, as shown in Fig. 1(b). The channel was fabricated by direct laser patterning at a repetition rate of 10 Hz, under a fluence of 2.0 J/cm2 (above the ablation threshold of the film), and using a programmable sample stage translation speed of 0.02 mm/s. The channel width was slightly larger than the beam diameter to avoid any significant interaction of the beam with the ablated edge of the film. The electrical current through the ITO channel was acquired using a source meter unit (Keithley, SMU2400) with a bias voltage of 0.05 V, at which resistive heating was negligible. The irradiation time was controlled by a mechanical shutter.
To investigate the optical response of the film during sub-damage threshold irradiation, a 532 nm continuous wave (CW) laser was built into the system. This laser was focused to a small probe size with a 1/e2 beam diameter of 6.0 μm, as shown in Fig. 1(c), using a Mitutoyo (NA: 0.42) objective lens. This beam width is very small compared to the size of the near infrared (NIR) pump beam (1/e2 beam diameter of 150 µm) which had a peak 1% fluence region of roughly 10 µm in diameter. The green probe beam was made co-incident with the NIR beam at a 45-degree incidence angle, as shown in Fig. 1(a). It was reflected from the film surface during irradiation and the reflected light was collected by a second, identical objective lens and delivered to a large area (⌀: 8 mm) photodetector with a 532 nm laser line filter to remove light scattered from the NIR pump laser. A lock-in-amplifier (Stanford Research, SR830), along with a 2 kHz chopper to modulate the incident probe laser, was used to detect subtle changes in the film’s optical properties. Images of the film were simultaneously captured in situ using a CCD camera (Thorlabs, DCU224C). The film in the images captured with the CCD is inclined with respect to the surface normal due to the 45° viewing angle of the camera.
3. Results and discussion
3.1 Multi-pulse laser damage with incubation effect
In order to determine an appropriate range of laser fluences for the investigation of the film’s sub-damage threshold electrical and optical properties, we performed multi-pulse laser damage tests over a range of fluences (F = 1 – 20 J/cm2) and pulse numbers (N = 1 – 3125). Figure 2 shows typical optical micrographs of the damage sites produced above the ablation thresholds for N = 1, 5, 25, and 3125. In this study, we defined damage as a modification to the film, which occurred via material removal, or ablation, and was apparently detectable using light microscopy. Upon single pulse irradiation at 7.7 J/cm2, the film was ablated at the center of the damage site as shown in Fig. 2(a). Ablative debris such as molten ejecta was observed near the edge of the ablated region as shown in the inset in Fig. 2(a). At a fluence of 5.6 J/cm2, laser ablation was not observed upon single pulse irradiation (data not shown). However, when the film was exposed to five pulses at the same fluence, the film was ablated at the center of the damage site in Fig. 2(b). This suggests that an incubation process occurs which increases light absorption within the irradiated area [18]. Based on the surface profile in Fig. 2(e) labeled by N = 5, corresponding to the dashed line in Fig. 2(b), the pink region near the edge of the damage site in Fig. 2(b) was thinner than the pristine region. The thinner film may be attributed to partial evaporation of the film surface upon laser irradiation. This would suggest that the peak temperature of the film near the edge of the damage site was close to the evaporation temperature, well above the melting temperature (> 2000 K). At this temperature, significant thermo-chemical [23] and/or thermo-mechanical [9] modifications of the film are expected. When the film was subjected to additional pulses, the region around the periphery of the damage site was further ablated. This is evident from the expansion of the damage sites with increasing number of pulse exposures shown in Fig. 2(b-d). It therefore appears as if the region around the periphery of the damage site becomes more absorptive after successive 1064 nm irradiation. Therefore, successive sub-threshold exposures effectively lower the damage threshold of the film below that of pristine ITO.
Fig. 2 (a-d) Optical micrographs of laser-induced damage sites for a range of laser fluences (F) and pulse numbers of exposure (N). All images have the same scale bar of 20 μm. (a) The region in the dashed box is shown at higher magnification in the inset. The scale bar in the inset is 5 μm. (e) The damage depth profiles along the dashed lines in (a-d) are shown in green, red, blue, and black, respectively.
The damage morphology shown in Fig. 2 was studied more systematically by measuring the size of the laser damage after the film was irradiated with a prescribed number of pulses at a given fluence. The square of the damage site diameters (D2) is plotted as a function of laser fluence on a semi-log scale in Fig. 3(a) for various numbers of pulses. The observed linear relationship is due to the Gaussian profile of the beam. For a Gaussian spatial beam profile with a 1/e2 laser beam radius of wo, the radial distribution of the laser fluence can be written as
where r represents the distance from the center of the beam and Fpeak is the peak laser fluence at r = 0. Substituting the beam diameter (D = 2r) and recognizing that F(r) is equal to the ablation threshold fluence, Fth, when D = 0 (for a given peak fluence, Fpeak), the following expression is found [26–28]:Following this derivation, we expect the square of the diameter (D2) to vary linearly with the log of the ratio between the peak applied fluence and the damage threshold fluence based on the beam profile. This relationship is clear in Fig. 3(a), emphasized by the solid arrow adjacent to the single pulse (N = 1) data. The damage growth behavior can also be visualized by plotting the damage area as a function of the number of pulses on a semi-log scale, as shown in Fig. 3(b). At fluences of 7, 9, 12, and 15 J/cm2, where the film was ablated after single pulse irradiation, the damage expanded continuously up to ~100 pulses. The size of the damage sites saturated above ~500 pulses. This is due to the finite size of the Gaussian beam profile (wo = 82.5 µm); the local laser fluence near the damage front substantially decreases as the damage expands [26]. At lower fluences (< 7 J/cm2), the film was ablated after multi-pulse irradiation. These damage sites expanded with increasing number of pulses, similar to the high fluence case, until saturating at a peak size for a large number of pulses. This can be inferred from the overlapping data sets of N = 625 and 3125 in Fig. 3(a). Figure 3(c) shows laser ablation thresholds over various number of pulses estimated by the zero area extrapolation method [28]. The dashed line was obtained using an empirical model,where Fth(X) is the ablation threshold upon N number of pulses, k is an incubation factor (an indication of how fast the material degrades or accumulates optically active defects), and N is the number of pulses [29]. The incubation factor (k) and the ablation threshold from an infinite number of pulse exposures (Fth(∞)) were obtained from a least-squares fitting and had values of 0.08 and 0.41 J/cm2, respectively. The fluence threshold ratio Fth(1000)/Fth(1) was calculated to be roughly 0.06, which is significantly lower than ratios (> 0.2) observed in previous multi-pulse ablation studies [26, 29, 30]. This low threshold ratio may be caused by enhanced degradation of the film due to the presence of optically active extrinsic defects, intrinsic point defects such as oxygen vacancies, or extended defects which could arise during laser-induced thermal cycling. However, we note that no damage was observed up to ~1.6 J/cm2 after 3125 pulses as presented with the red dot in Fig. 3(a) but damage was observed at ~1.8 J/cm2. Therefore, we used fluences in the range of ~1.0 J/cm2 to ~1.8 J/cm2 to examine the electrical and optical properties of the film under sub-damage threshold irradiation, as indicated by the red dashed line in Fig. 3(c).Fig. 3 The square of the damage site diameters is plotted as a function of (a) the laser fluence and (b) the number of pulses (N) on a semi-log scale for N = 1, 5, 25, 125, 625, and 3125. (c) Estimated laser ablation threshold as a function of the number of pulses on a semi-log scale.
3.2 Electrical resistance of ITO film under multi-pulse laser exposures
In order to monitor the electrical response of the ITO film below the damage threshold, the NIR beam was positioned in the middle of the laser-etched conductive ITO channel as indicated by the arrow in Fig. 4(a). Its position remained fixed throughout the measurements. The laser fluence was increased from 0.8 to 1.8 J/cm2 and the resistance of the ITO channel was recorded for 500 s for each fluence setting. During the measurement, the film was exposed to the beam for the time interval between 100 to 400 s (for a total of 3000 pulses at 10 Hz), as outlined in the dashed box in Fig. 4(a, b). In Fig. 4(a), no noticeable change in film resistance was detected upon the laser irradiation at fluences from 0.8 to 1.6 J/cm2, however the electrical resistance drastically increased after irradiation at a fluence of 1.8 J/cm2. The drastic resistance increase is attributed to the channel width reduction that was caused by the initiation of laser damage and the growth of the damage site into the channel as shown in the left inset of Fig. 4(a). In order to capture small changes in resistance for the 0.8 – 1.6 J/cm2 measurements, the R(t) values in Fig. 4(a) were converted to resistance change values using ∆R(t)/Ro × 100 (%), where Ro = R(t = 0) and ∆R(t) = R(t) – Ro. Note, 0.02% offsets were applied to each plot to avoid overlapping data. Using this representation, the five irradiation cycles at fluences up to 1.6 J/cm2 again show no significant resistance change, as shown in Fig. 4(b). Thus, the electrical resistance of the ITO film appears to have been maintained up to the lifetime damage threshold (~1.6 J/cm2). In order to improve the signal to noise ratio, the same approach was applied to narrower channel structures. However, when the channel width (e.g. 50 μm) was narrower than the beam size (~150 μm), damage propagated from the channel edge at fluences lower than 1.6 J/cm2 due to increased absorption in the ablated ITO film edges.
Fig. 4 Electrical resistance of ITO film under ns laser irradiation at fluences of 0.8, 1.0, 1.2, 1.4, 1.6, and 1.8 J/cm2. The dashed box indicates the time frame of laser irradiation. (a) Transient response of electrical resistance (R) from ITO channel structure. The left inset shows the 200 µm ITO channel structure that was damaged during the measurement at 1.8 J/cm2. The right inset shows a magnified graph before the resistance increase at 1.8 J/cm2 due to the damage. (b) Transient response of electrical resistance change (∆R/Ro) under laser irradiation at 0.8 – 1.6 J/cm2. Note, 0.02% offsets were applied to each plot to avoid overlapping graphs.
3.3 Optical reflectance of ITO film under multi-pulse laser exposures
In order to determine whether sub-threshold exposures could affect the optical properties of the transparent conductive ITO film, we examined the surface morphology of the film under multi-pulse exposures at fluences of 0.5, 1.0, 1.5, and 2.0 J/cm2 using an in situ camera. At fluences of 0.5, 1.0, and 1.5 J/cm2, no noticeable change was detected (data not shown). Figure 5(a) shows snapshots of the measurement at a fluence of 2.0 J/cm2 and the elapsed time of each snapshot is presented in the top left corner of the image. During the measurement, the film was exposed to the NIR beam between 100 and 400 s (for a total of 3000 pulses at 10 Hz), identical to the conditions used for the resistance measurements. As shown in Fig. 5(a), damage was detected at 104 s (or after exposure to 40 pulses) at the location on the film indicated by the white arrow. The damage then expanded upon subsequent irradiation. The damage growth terminated after approximately 150 s (after exposure to 500 pulses), analogous to the behavior shown in Fig. 3(b). In addition, based on multiple tests at 2.0 J/cm2 (data not shown), final damage morphologies were almost identical, suggesting that the damage growth for a given ITO film is deterministic for a given fluence, spatial beam profile, and total number of pulses. However, we also found that the damage initiation time and location were not exactly reproducible. Figure 5(b) shows the reflected signal of the co-incident probe beam measured simultaneously with the snapshots. The black line corresponds to the measurement in Fig. 5(a) and the blue line corresponds to a separate measurement under the same exposure conditions. The damage initiation and growth were observed as a fluctuation of the reflected intensity as indicated with asterisk symbols. Damage initiated at approximately 104 s during the measurement shown in black, and at approximately 208 s during the measurement shown blue. As the damage grew, the substrate became exposed by ablation of the film, which resulted in a decrease in the reflected signal.
Fig. 5 Optical reflectance of ITO film under ns laser irradiation. (a) In situ camera snapshots of ITO film surface upon multi-pulse exposures at a laser fluence of 2.0 J/cm2. The elapsed time of each snapshot is presented in the left top corner. All images have the same scale, where the scale bars are 50 μm. The inset in the 104 s image shows first observable damage with 3 × magnification. (b) Reflected intensity at 532 nm of two separate runs at 2.0 J/cm2. The black dots in the snapshots in (a) indicate the probe beam location for the reflection intensity measurement. (c) Magnified reflection intensity change at fluences of 0.5, 1.0, 1.5, and 2.0 J/cm2. The irradiation time was from 100 to 400 s. Note, 0.75% offsets were applied to each plot to avoid overlapping graphs.
Although there were no noticeable changes in the film prior to damage initiation based on the snapshots in Fig. 5(a), we did capture subtle changes in the reflected probe signal when using a lock-in-amplifier to increase the measurement sensitivity. Figure 5(c) shows magnified reflectance changes of the film during the 2.0 J/cm2 irradiation measurement (blue). Exposures at 0.5, 1.0, and 1.5 J/cm2 were also performed in the same location prior to the 2.0 J/cm2 measurement. The reflectance of the film immediately decreased after 2.0 J/cm2 irradiation as shown in Fig. 5(c), indicating a modification of the film above the lifetime damage threshold (~1.6 J/cm2), as expected. At lower fluences (0.5, 1.0, and 1.5 J/cm2), damage was not observed upon exposure to 3000 pulses and no changes in reflectance were apparent. Consequently, when the fluence is higher than the lifetime laser damage threshold, the ITO film is modified and the modifications accumulate during subsequent pulses, eventually leading to damage. The modifications were evident from reductions in reflected green light, or “darkening”, and may be attributed to thermomechanical stress induced cracks [9] or thermochemical modification [23], e.g. oxygen vacancy formation or tin oxide reduction due to fast heating/cooling. Prior work has shown that the “darkening” of ITO films at 532 nm can be caused by scattering by cracks or a plasma frequency blue shift via the thermochemical modification [9, 23, 31]. Both can also result in increased light absorption at 1064 nm and thereby induce a positive feedback mechanism in which more light is absorbed as more damage is produced and more damage is produced as more light is absorbed. In contrast, when the fluence is lower than the lifetime laser damage threshold, properties such as resistance and reflectivity are maintained upon multi-pulse irradiation, which ensures reliable and efficient operation.
In addition, we did not observe laser-induced periodic surface structures (LIPSS), which are typically formed in ITO films after femtosecond laser irradiation [32–34]. This suggests that the film (thickness: 200 nm, sheet resistance: 82 Ω/sq, substrate: fused silica) used in this study is not optimal to produce LIPSS upon irradiation of ns laser pulses (1064 nm, 4.7 ns, 10 Hz). The film was continuously damaged or ablated above the damage threshold and no apparent LIPSS structures were visible below the damage threshold.
4. Conclusions
Multi-pulse damage tests were performed on a single ITO film using a 1064 nm near-infrared laser with 4.7 ns pulse durations. Upon multi-pulse exposure, damage was initiated at fluences above the film’s lifetime damage threshold, which was roughly 30% of the single-pulse laser ablation threshold. Laser-induced film modification was observed during in situ reflectance measurements with a 532 nm source prior to damage initiation. This modification was amplified with subsequent pulses, resulting in damage formation and expansion. When the fluence was lower than the lifetime laser damage threshold, no film modification was detected and the electrical and optical properties were maintained. Therefore, it is concluded that ITO films may be operated within optoelectronic devices below their lifetime thresholds without noticeable performance degradation.
Funding
U.S. Department of Energy (DOE) (DE-AC52-07NA27344); Lawrence Livermore National Laboratory (LLNL); Laboratory Directed Research and Development grant (15-ERD-057)
Acknowledgments
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344 within the LDRD program.
References and links
1. C. G. Granqvist and A. Hultaker, “Transparent and conducting ITO films: new developments and applications,” Thin Solid Films 411(1), 1–5 (2002). [CrossRef]
2. M. J. Alam and D. C. Cameron, “Optical and electrical properties of transparent conductive ITO thin films deposited by sol-gel process,” Thin Solid Films 377-378, 455–459 (2000). [CrossRef]
3. K. Ellmer, “Past achievements and future challenges in the development of optically transparent electrodes,” Nat. Photonics 6(12), 809–816 (2012). [CrossRef]
4. J. Wallace, “Four 800 kW laser-diode arrays to pump high-pulse-rate HAPLS petawatt laser,” Laser Focus World 51, 15–16 (2015).
5. J. Heebner, M. Borden, P. Miller, C. Stolz, T. Suratwala, P. Wegner, M. Hermann, M. Henesian, C. Haynam, S. Hunter, K. Christensen, N. Wong, L. Seppala, G. Brunton, E. Tse, A. Awwal, M. Franks, E. Marley, K. Williams, M. Scanlan, T. Budge, M. Monticelli, D. Walmer, S. Dixit, C. Widmayer, J. Wolfe, J. Bude, K. McCarty, and J. M. DiNicola, “A programmable beam shaping system for tailoring the profile of high fluence laser beams,” Proc. SPIE 7842, 78421C (2010). [CrossRef]
6. P. Radhakrishnan, K. Sathianandan, and N. Subhash, “Laser-Induced Damage to Spray Pyrolysis Deposited Transparent Conducting Films,” J. Appl. Phys. 59(3), 902–904 (1986). [CrossRef]
7. C. Wolfe, M. Kozlowski, J. Campbell, M. Staggs, and F. Rainer, “Permanent laser conditioning of thin film optical materials,” US Patent, 5472748 A (1995).
8. S. Elhadj, J. H. Yoo, R. A. Negres, M. G. Menor, J. J. Adams, N. Shen, D. A. Cross, I. L. Bass, and J. Bude, “Optical damage performance of conductive widegap semiconductors: spatial, temporal, and lifetime modeling,” Opt. Mater. Express 7(1), 202–212 (2017). [CrossRef]
9. J. H. Yoo, M. G. Menor, J. J. Adams, R. N. Raman, J. R. Lee, T. Y. Olson, N. Shen, J. Suh, S. G. Demos, J. Bude, and S. Elhadj, “Laser damage mechanisms in conductive widegap semiconductor films,” Opt. Express 24(16), 17616–17634 (2016). [CrossRef] [PubMed]
10. N. Subhash and K. Sathianandan, “Laser-Induced Damage to Transparent Conducting SnO2 Films at 1062 nm,” J. Appl. Phys. 54(1), 423–424 (1983). [CrossRef]
11. W. T. Pawlewicz, I. B. Mann, W. H. Lowdermilk, and D. Milam, “Laser-Damage-Resistant Transparent Conductive Indium Tin Oxide Coatings,” Appl. Phys. Lett. 34(3), 196–198 (1979). [CrossRef]
12. T. Minami, “Transparent conducting oxide semiconductors for transparent electrodes,” Semicond. Sci. Technol. 20(4), S35–S44 (2005). [CrossRef]
13. S. Naseem and T. J. Coutts, “The Influence of Deposition Parameters on the Optical and Electrical-Properties of Rf-Sputter-Deposited Indium Tin Oxide-Films,” Thin Solid Films 138(1), 65–70 (1986). [CrossRef]
14. P. C. Karulkar and M. E. Mccoy, “Dc Magnetron Sputter Deposition of Indium Tin Oxide-Films,” Thin Solid Films 83(2), 259–260 (1981). [CrossRef]
15. G. S. Belo, B. J. P. da Silva, E. A. de Vasconcelos, W. M. de Azevedo, and E. F. da Silva Jr., “A simplified reactive thermal evaporation method for indium tin oxide electrodes,” Appl. Surf. Sci. 255(3), 755–757 (2008). [CrossRef]
16. M. Yamaguchi, A. Ide-Ektessabi, H. Nomura, and N. Yasui, “Characteristics of indium tin oxide thin films prepared using electron beam evaporation,” Thin Solid Films 447-448, 115–118 (2004). [CrossRef]
17. F. O. Adurodija, R. Bruning, I. O. Asia, H. Izumi, T. Ishihara, and H. Yoshioka, “Effects of laser irradiation energy density on the properties of pulsed laser deposited ITO thin films,” Appl. Phys. Adv. Mater. 81, 953–957 (2005).
18. J. H. Kim, K. A. Jeon, G. H. Kim, and S. Y. Lee, “Electrical, structural, and optical properties of ITO thin films prepared at room temperature by pulsed laser deposition,” Appl. Surf. Sci. 252(13), 4834–4837 (2006). [CrossRef]
19. S. Y. Park, K. H. Ji, H. Y. Jung, J. I. Kim, R. Choi, K. S. Son, M. K. Ryu, S. Lee, and J. K. Jeong, “Improvement in the device performance of tin-doped indium oxide transistor by oxygen high pressure annealing at 150 degrees C,” Appl. Phys. Lett. 100(16), 162108 (2012). [CrossRef]
20. A. Rogozin, N. Shevchenko, M. Vinnichenko, F. Prokert, V. Cantelli, A. Kolitsch, and W. Moller, “Real-time evolution of the indium tin oxide film properties and structure during annealing in vacuum,” Appl. Phys. Lett. 85(2), 212–214 (2004). [CrossRef]
21. W. Chung, M. O. Thompson, P. Wickboldt, D. Toet, and P. G. Carey, “Room temperature indium tin oxide by XeCl excimer laser annealing for flexible display,” Thin Solid Films 460(1-2), 291–294 (2004). [CrossRef]
22. H. Han, J. W. Mayer, and T. L. Alford, “Band gap shift in the indium-tin-oxide films on polyethylene napthalate after thermal annealing in air,” J. Appl. Phys. 100(8), 083715 (2006). [CrossRef]
23. T. Szorenyi, L. D. Laude, I. Bertoti, Z. Kantor, and Z. Geretovszky, “Excimer-Laser Processing of Indium-Tin-Oxide Films - an Optical Investigation,” J. Appl. Phys. 78(10), 6211–6219 (1995). [CrossRef]
24. K. Shinoda, T. Nakajima, and T. Tsuchiya, “In situ monitoring of excimer laser annealing of tin-doped indium oxide films for the development of a low-temperature fabrication process,” Appl. Surf. Sci. 292, 1052–1058 (2014). [CrossRef]
25. H. F. Wang, Z. M. Huang, D. Y. Zhang, F. Luo, L. X. Huang, Y. L. Li, Y. Q. Luo, W. P. Wang, and X. J. Zhao, “Thickness effect on laser-induced-damage threshold of indium-tin oxide films at 1064 nm,” J. Appl. Phys. 110(11), 113111 (2011). [CrossRef]
26. J. Bonse, J. M. Wrobel, J. Kruger, and W. Kautek, “Ultrashort-pulse laser ablation of indium phosphide in air,” Appl. Phys. Adv. Mater. 72, 89–94 (2001).
27. J. M. Liu, “Simple Technique for Measurements of Pulsed Gaussian-Beam Spot Sizes,” Opt. Lett. 7(5), 196–198 (1982). [CrossRef] [PubMed]
28. A. Ben-Yakar and R. L. Byer, “Femtosecond laser ablation properties of borosilicate glass,” J. Appl. Phys. 96(9), 5316–5323 (2004). [CrossRef]
29. A. Rosenfeld, M. Lorenz, R. Stoian, and D. Ashkenasi, “Ultrashort-laser-pulse damage threshold of transparent materials and the role of incubation,” Appl. Phys. Adv. Mater. 69, S373–S376 (1999).
30. S. Z. Xiao, E. L. Gurevich, and A. Ostendorf, “Incubation effect and its influence on laser patterning of ITO thin film,” Appl. Phys. Adv. Mater. 107, 333–338 (2012).
31. W. G. Spitzer and H. Y. Fan, “Determination of Optical Constants and Carrier Effective Mass of Semiconductors,” Phys. Rev. 106(5), 882–890 (1957). [CrossRef]
32. C. Wang, H. I. Wang, C. W. Luo, and J. Leu, “Anisotropic optical transmission of femtosecond laser induced periodic surface nanostructures on indium-tin-oxide films,” Appl. Phys. Lett. 101(10), 101911 (2012). [CrossRef] [PubMed]
33. M. Klotzer, M. Afshar, D. Feili, H. Seidel, K. Konig, and M. Straub, “Generation of laser-induced periodic surface structures in indium-tin-oxide thin films and two-photon lithography of ma-N photoresist by sub-15 femtosecond laser microscopy for liquid crystal cell application,” Proc. SPIE 9351, 935110 (2015).
34. C. Wang, H. I. Wang, W. T. Tang, C. W. Luo, T. Kobayashi, and J. Leu, “Superior local conductivity in self-organized nanodots on indium-tin-oxide films induced by femtosecond laser pulses,” Opt. Express 19(24), 24286–24297 (2011). [CrossRef] [PubMed]
