The electrical instability behaviors of a positive-gate-bias-stressed amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistor (TFT) are studied under monochromatic light illumination. It is found that as the wavelength of incident light reduces from 750 nm to 450 nm, the threshold voltage of the illuminated TFT shows a continuous negative shift, which is caused by photo-excitation of trapped electrons at the channel/dielectric interface. Meanwhile, an increase of the sub-threshold swing (SS) is observed when the illumination wavelength is below 625 nm ($2.0 eV). The SS degradation is accompanied by a simultaneous increase of the field effect mobility (l FE) of the TFT, which then decreases at even shorter wavelength beyond 540 nm ($2.3 eV). The variation of SS and l FE is explained by a physical model based on generation of singly ionized oxygen vacancies (V o þ) and double ionized oxygen vacancies (V o 2þ) within the a-IGZO active layer by high energy photons, which would form trap states near the mid-gap and the conduction band edge, respectively.
Engineering metamaterials with tunable resonances are of great importance for improving the functionality and flexibility of terahertz (THz) systems. An ongoing challenge in THz science and technology is to create large-area active metamaterials as building blocks to enable efficient and precise control of THz signals. Here, an active metamaterial device based on enhancement-mode transparent amorphous oxide thin-film transistor arrays for THz modulation is demonstrated. Analytical modelling based on full-wave techniques and multipole theory exhibits excellent consistent with the experimental observations and reveals that the intrinsic resonance mode at 0.75 THz is dominated by an electric response. The resonant behavior can be effectively tuned by controlling the channel conductivity through an external bias. Such metal/oxide thin-film transistor based controllable metamaterials are energy saving, low cost, large area and ready for mass-production, which are expected to be widely used in future THz imaging, sensing, communications and other applications.
We demonstrate optoelectronic devices implemented on suspended p-n junction InGaN/GaN multiple quantum wells (MQWs) for the further monolithic integration of an optical source, a waveguide, and a photodetector on the same GaN-on-silicon wafer. The fabricated suspended membrane device exhibits selectable functionalities either for efficient light-emitting diodes (LEDs) or sensitive photodetectors. Typical current-voltage (I-V) characteristics are obtained for the device operated under the LED mode, and the emitted light intensity is effectively modulated by the applied voltage. Lateral in-plane propagation of emitted light in a suspended membrane is experimentally presented. The simulation results show that the thickness-dependent optical performance can be tuned by back wafer thinning for epitaxial films. The device operated under the photodetector mode exhibits a static photocurrent on-off ratio s of 2:25 Â 10 5 at a 1-V bias voltage with the illumination power of 690 W and the wavelength of 450 nm. The photocurrent also shows a rectangular pulse response of the same duration as a 1-s rectangular illumination pulse at a 0-V bias voltage with the illumination power of 1 mW. The temporal photocurrent on-off ratio t is around 1:01 Â 10 5 . This paper opens a promising way to realize the monolithic integration of a LED, a waveguide, and a photodetector on a GaN-on-silicon platform.
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