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Indium tin oxide (ITO) has become a very useful plasmonic and nonlinear optical material because of its highly tunable electrical and optical properties and strong optical nonlinearity. In this work, the authors conducted detailed fabrication process studies by using high-temperature reactive sputtering to finely tune the optical properties of ITO thin films, particularly the epsilon-near-zero (ENZ) wavelength in the near and mid-IR spectrum. Sputtered ITO thin films are characterized by using spectroscopic ellipsometry, surface profilometry, Hall measurements, and 4-point probe testing. Additionally, the effect of post-deposition annealing of ITO films is also investigated.
Addition of wavelength selective absorbers on microbolometers tends to increase their thermal mass and slow their infrared response times. Making the bolometric material an integral part of the absorber and minimizing layer thicknesses is one possible way to maintain high detector speeds. Here, we study experimentally the effect on permittivity of adding a layer of semiconducting VOx between two layers of SiO2. Additionally, we investigate theoretically the effect on resonance wavelength of thinning the metal in metal-insulator-metal plasmonic resonant absorbers.
The illumination instabilities of nanocrystalline ZnO thin-film transistors (TFT) with HfO2 gate dielectrics are reported via zero gate bias multiwave length illumination stress method. TFT ID–VG curves exhibit a negative threshold voltage shift together with an increase in ID off current and increase in subthreshold slope with increasing photon energy and illumination time. Analysis of transistor characteristics indicates that one component governing negative threshold voltage shifts is a decrease in grain boundary-trapped charge areal density due to illumination. This relationship can be explained by conduction based on thermionic emission over potential barriers formed at the ZnO crystallite boundaries. ID off-state current trends with photon energy in a manner consistent with exponentially decreasing absorption below the conduction band edge.
Nanocrystalline ZnO thin films grown by the pulsed laser deposition technique were used to fabricate high performance thin film transistors suitable for RF applications. It was shown that drain current on/off ratios of higher than 1×1012, sub-threshold voltage swing values lower than 100 mV/decade and hysteresis-free operation could be maintained with films grown across a wide temperature range (25°C to 400°C). Films grown at 200°C have the lowest surface roughness and result in devices with the highest current density operation. Devices with 1.2 μm gate lengths and Au-based gate metals had record current gain and power gain cut off frequencies of fT = 2.9 GHz and fmax = 10 GHz, respectively.
Temperature-dependent Hall-effect measurements have been performed on three Ga-doped ZnO thin films of various thicknesses (65, 177, and 283 nm), grown by pulsed laser deposition at 400 °C and annealed at 400 °C for 10 min in Ar, N2, or forming-gas (5% H2 in Ar). The donor ND and acceptor NAconcentrations as a function of sample thickness and annealing conditions are determined by a new formalism that involves only ionized-impurity and boundary scattering. Before annealing, the samples are highly compensated, with ND = (2.8 ± 0.3) × 1020 cm-3 and NA = (2.6 ± 0.2) × 1020 cm-3. After annealing in Ar the samples are less compensated, with ND = (3.7 ± 0.1) × 1020 cm-3 and NA = (2.0 ± 0.1) × 1020 cm-3; furthermore, these quantities are nearly independent of thickness. However, after annealing in N2 and forming-gas, ND and NA are thickness dependent, partly due to depth-dependent diffusion of N2 and H, respectively.
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