Comparative Study of Second-Harmonic Generation from Epsilon-Near-Zero Indium Tin Oxide and Titanium Nitride Nanolayers Excited in the Near-Infrared Spectral Range

Abstract

We perform a comparative study of second-harmonic generation (SHG) from indium tin oxide (ITO) and from titanium nitride (TiN) nanolayers excited in the near-infrared spectrum. Both materials are compatible with Si technology and are candidate platforms for integrated nonlinear optics. In this work, we fabricate ITO samples with an ε-near-zero (ENZ) condition, which can be continuously tailored in the 1150−1670 nm spectral range, and TiN samples with a metallic behavior in the same spectral range. For the ITO nanolayers, we observe tunability and enhancement of the SHG intensity when the samples are excited at their respective ENZ condition, in agreement with the electromagnetic modeling and analogous to its third-harmonic generation studied earlier. On the other hand, we show that the SHG efficiency of TiN nanolayers is lower by a factor of 50. We determine experimentally that the dominant component of the second-order susceptibility for our best ITO nanolayer is χ zzz (2ω) = 0.18 pm V −1 , and we theoretically predict that the SHG process is enhanced up to 4 orders of magnitude when resonantly pumping the nanolayer at the ENZ wavelength with respect to a wavelength at 2000 nm. Remarkably, the resulting SHG efficiency is comparable with a crystalline quartz plate with thickness 0.5 mm used as a reference in our experiments in reflection configuration. Our study clearly indicates that ITO nanolayers with engineered ENZ conditions are a promising material platform for surface nonlinearities, with possible applications to nonlinear metasurfaces, Si-based flat optics, and sensing.

Self-interaction of ultrashort pulses in an epsilon-near-zero nonlinear material at the telecom wavelength

“…It is also worthy to mention that the second-and third-order nonlinear susceptibilities of ITO near the ENZ point make it possible to implement SHG and THG effects in this material [21,22]. In this connection, the present results suggest that the energy of longer-wavelength incident light can be stored and accumulated in the sample by means of the energy-localization mechanism demonstrated here.…”

Study of second and third harmonic generation from an indium tin oxide nanolayer: Influence of nonlocal effects and hot electrons

“…times larger compared to that of crystalline bulk silicon. In reference [12], a comparative study of ITO and TiN nanolayers showed an enhancement of SHG from ITO at the ENZ wavelength.…”

“…The resistivity of ITO is attributed to oxygen vacancy and film crystallinity. Therefore the deposition conditions as well as post-annealing process allow one to tune the ENZ wavelength[11,12].Our 20-nm thick sample was annealed at 600ºC and displays an ENZ condition near 1260nm. It has been shown that the electro-optical properties of ITO can be thicknessdependent even under the same deposition conditions, and thus may exhibit a different ENZ condition.…”

Second Harmonic Generation from Phononic Epsilon-Near-Zero Berreman Modes in Ultrathin Polar Crystal Films

“…38,39 However, these previous studies mostly focused on the linear optical response, whereas only few reports of the nonlinear conversion efficiency of ultrathin films exist. This efficiency has been proposed to be strongly enhanced at ENZ frequencies, 40 but experimental verification is limited to a few studies of indium tin oxide (ITO) thin layers [41][42][43] excited at frequencies in the near infrared spectral range. The nonlinear optical response of thin films of other materials with phonon resonances in the midto far-IR, in particular III-V or III-nitride polar semiconductor compounds, however, has to the best of our knowledge not yet been studied.…”