Photogating interfacial effects in carbon nanotube-based transistors on a Si/SiO2 substrate toward highly sensitive photodetection.

Single-walled carbon nanotubes (SWCNTs) are considered to be promising material platforms for various photodetectors (including phototransistors) due to their unique optoelectrical properties (e.g., high mobility and a wide variety of bandgap values). Herein, we present highly sensitive phototransistors which utilised sparse networks of SWCNTs on a silicon/silica substrate and operated by means of the photogating effect. The response of SWCNTs to photo-induced electrostatic charges (photogating effect) was highly dependent on the conductivity type of the channel, which was "metallic" or "semiconducting", depending on the SWCNT density. We determined the performance of these transistors depending on the characteristics of the substrate and conductivity type of the SWCNT channel. The optimized configuration of phototransistors with a channel comprising a sparse network of SWCNTs permitted improvement in the specific detectivity and relative response compared with previously reported photodetectors based on graphene and carbon nanotubes. We demonstrated an absolute responsivity of ∼60 A W-1 at an incident light power of ∼2 nW, specific detectivity of 7.8 × 1011 cm·Hz1/2 W-1, and response time of 300 µs. These data revealed the high potential of photogating-based SWCNTs detectors for extremely weak signals with a high signal-to-noise ratio.

Dumbbell-Shaped Ho-Doped Fiber Laser Mode-Locked by Polymer-Free Single-Walled Carbon Nanotubes Saturable Absorber.

We propose a simple dumbbell-shaped scheme of a Holmium-doped fiber laser incorporating a minimum number of optical elements. Mode-locking regimes were realized with the help of polymer-free single-walled carbon nanotubes (SWCNTs) synthesized using an aerosol (floating catalyst) CVD method. We show that such a laser scheme is structurally simple and more efficient than a conventional one using a ring cavity and a similar set of optical elements. In addition, we investigated the effect of SWCNT film transmittance, defined by the number of 40 nm SWCNT layers on the laser's performance: operating regimes, stability, and self-starting. We found that three SWCNT layers with an initial transmittance of about 40% allow stable self-starting soliton mode-locking at a wavelength of 2076 nm with a single pulse energy of 0.6 nJ and a signal-to-noise ratio of more than 60 dB to be achieved.

Ionic Liquid Gated Carbon Nanotube Saturable Absorber for Switchable Pulse Generation.

Materials with electrically tunable optical properties offer a wide range of opportunities for photonic applications. The optical properties of the single-walled carbon nanotubes (SWCNTs) can be significantly altered in the near-infrared region by means of electrochemical doping. The states' filling, which is responsible for the optical absorption suppression under doping, also alters the nonlinear optical response of the material. Here, for the first time we report that the electrochemical doping can tailor the nonlinear optical absorption of SWCNT films and demonstrate its application to control pulsed fiber laser generation. With a pump-probe technique, we show that under an applied voltage below 2 V the photobleaching of the material can be gradually reduced and even turned to photoinduced absorption. Furthermore, we integrated a carbon nanotube electrochemical cell on a side-polished fiber to tune the absorption saturation and implemented it into the fully polarization-maintaining fiber laser. We show that the pulse generation regime can be reversibly switched between femtosecond mode-locking and microsecond Q-switching using different gate voltages. This approach paves the road toward carbon nanotube optical devices with tunable nonlinearity.

Holey single-walled carbon nanotubes for ultra-fast broadband bolometers.

Although carbon nanotubes have already been demonstrated to be a promising material for bolometric photodetectors, enhancing sensitivity while maintaining the speed of operation remains a great challenge. Here, we present a holey carbon nanotube network, designed to improve the temperature coefficient of resistance for highly sensitive ultra-fast broadband bolometers. Treatment of carbon nanotube films with low-frequency oxygen plasma allows fine tuning of the electronic properties of the material. The temperature coefficient of resistance of our films is much greater than the reported values for pristine carbon nanotubes, up to -2.8% K-1 at liquid nitrogen temperature. The bolometer prototypes made from the treated films demonstrate high sensitivity over a wide IR range, a short response time, smooth spectral characteristics and a low noise level.