We show that despite of low loss, silver and gold are not suitable for a variety of nanoplasmonic applications in the infrared range, which require compact modes in single-interface plasmonic waveguides. At the same time, degenerate wide-band-gap semiconductors can serve as high-quality plasmonic materials at telecom wavelengths, combining fairly high compactness and relatively low loss. Their plasmonic properties in the near-infrared can be compared to those of gold in the visible range. The same materials can be used in a variety of non-plasmonic metamaterials applications, including transformation optics and invisibility cloaking.

This letter reports on the metal-like conductivity down to 125K in highly crystalline transparent (⩾85% in the visible region) Al:ZnO films grown on sapphire and glass substrates by pulsed-laser deposition technique. Significantly different surface morphologies were found on both types of films. Temperature dependent resistivity measurements of the films grown at 450°C on sapphire and glass show metal-like conductivity with electrical resistivity, ∼1.77×10−4 and ∼3.92×10−4Ωcm, respectively, at room temperature followed by either a residual conductivity or a metal-semiconductor transition at low temperature due to the localization effect caused by the defects.

Plasmonic materials (PMs), featuring large static or dynamic tunability, have significant impact on the optical properties due to their potential for applications in transformation optics, telecommunications, energy, and biomedical areas. Among PMs, the carrier concentration and mobility are two tunable parameters, which control the plasma frequency of a metal. Here, we report on large static and dynamic tunability in wavelengths up to 640 nm in Al-doped ZnO based transparent conducting degenerate semiconductors by controlling both thickness and applied voltages. This extreme tunability is ascribed to an increase in carrier concentration with increasing thickness as well as voltage-induced thermal effects that eventually diminish the carrier concentration and mobility due to complex chemical transformations in the multilayer growth process. These observations could pave the way for optical manipulation of this class of materials for potential transformative applications.

We report on the significant enhancement of photocurrent in pn heterojunction diode, consisting of n-CdSe∕p-Si substrates, in situ deposited with Au nanoparticles on the surface by the pulsed-laser deposition technique. This is attributed due to the large enhancement in electromagnetic field that occurs in the vicinity of the metal surface, causing surface plasmons. The large enhancement in Raman and photoluminescence intensity was observed due to surface plasmon resonance. Our results suggest that the photodetectors, optoelectronic, such as high-performance thin-film solar cells, optical communication, and sensing devices, including bio- and molecular sensors, can be fabricated with improved functionality.

Al-doped ZnO films were grown on glass substrates by the pulsed-laser deposition technique with varying substrate temperatures. The optical band gap decreases from 3.64 to 3.46 eV as the substrate temperature increases from 350 to 450 • C, illustrating the increase in Al content in the context of a degenerate semiconductor, and can be explained in the framework of the Burstein-Moss effect. All films show optical transparency greater than 85%. Al:ZnO films show a metal-semiconductor transition to metal-like behavior as the substrate temperature increases from 350 to 450 • C. The observed metal-like and metal-semiconductor transitions are explained by taking into account the Mott phase transition and localization effects due to defects. The resistivity decreases from 896 to 470 µ cm as the substrate temperature increases from 350 to 450 • C. In addition, the competition between the thermally activated carriers and scattering effects of free carriers in a degenerate semiconductor can also explain the metal-semiconductor transition.