Levent E. Aygun

Plasmonically enhanced hot electron based photovoltaic device

Hot electron photovoltaics is emerging as a candidate for low cost and ultra thin solar cells. Plasmonic means can be utilized to significantly boost device efficiency. We separately form the tunneling metal-insulator-metal (MIM) junction for electron collection and the plasmon exciting MIM structure on top of each other, which provides high flexibility in plasmonic design and tunneling MIM design separately. We demonstrate close to one order of magnitude enhancement in the short circuit current at the resonance wavelengths.

Thin film MoS 2 nanocrystal based ultraviolet photodetector

We report on the development of UV range photodetector based on molybdenum disulfide nanocrystals (MoS₂-NCs). The inorganic MoS₂-NCs are produced by pulsed laser ablation technique in deionized water and the colloidal MoS₂-NCs are characterized by transmission electron microscopy, Raman spectroscopy, X-ray diffraction and UV/VIS absorption measurements. The photoresponse studies indicate that the fabricated MoS₂-NCs photodetector (MoS₂-NCs PD) operates well within 300-400 nm UV range, with diminishing response at visible wavelengths, due to the MoS₂-NCs absorption characteristics. The structural and the optical properties of laser generated MoS₂-NCs suggest promising applications in the field of photonics and optoelectronics.

Dynamic Control of Photoresponse in ZnO-Based Thin-Film Transistors in the Visible Spectrum

We present ZnO-channel thin-film transistors with actively tunable photocurrent in the visible spectrum, although ZnO band edge is in the ultraviolet. ZnO channel is deposited by atomic layer deposition technique at a low temperature (80 °C), which is known to introduce deep level traps within the forbidden band of ZnO. The gate bias dynamically modifies the occupancy probability of these trap states by controlling the depletion region in the ZnO channel. Unoccupied trap states enable the absorption of the photons with lower energies than the bandgap of ZnO. Photoresponse to visible light is controlled by the applied voltage bias at the gate terminal.

Amyloid-like peptide nanofiber templated titania nanostructures as dye sensitized solar cell anodic materials

One-dimensional titania nanostructures can serve as a support for light absorbing molecules and result in an improvement in the short circuit current (Jsc) and open circuit voltage (Voc) as a nanostructured and high-surface-area material in dye-sensitized solar cells. Here, self-assembled amyloid-like peptide nanofibers were exploited as an organic template for the growth of one-dimensional titania nanostructures. Nanostructured titania layers were utilized as anodic materials in dye sensitized solar cells (DSSCs). The photovoltaic performance of the DSSC devices was assessed and an enhancement in the overall cell performance compared to unstructured titania was observed.

Low temperature atomic layer deposited ZnO photo thin film transistors

ZnO thin film transistors (TFTs) are fabricated on Si substrates using atomic layer deposition technique. The growth temperature of ZnO channel layers are selected as 80, 100, 120, 130, and 250 °C. Material characteristics of ZnO films are examined using x-ray photoelectron spectroscopy and x-ray diffraction methods. Stoichiometry analyses showed that the amount of both oxygen vacancies and interstitial zinc decrease with decreasing growth temperature. Electrical characteristics improve with decreasing growth temperature. Best results are obtained with ZnO channels deposited at 80 °C; Ion/Ioff ratio is extracted as 7.8 × 109 and subthreshold slope is extracted as 0.116 V/dec. Flexible ZnO TFT devices are also fabricated using films grown at 80 °C. ID–VGS characterization results showed that devices fabricated on different substrates (Si and polyethylene terephthalate) show similar electrical characteristics. Sub-bandgap photo sensing properties of ZnO based TFTs are investigated; it is shown that visible light absorption of ZnO based TFTs can be actively controlled by external gate bias.

TiO2 thin film transistor by atomic layer deposition

In this study, TiO2 films were deposited using thermal Atomic Layer Deposition (ALD) system. It is observed that asdeposited ALD TiO2 films are amorphous and not suitable as TFT channel material. In order to use the film as channel material, a post-annealing process is needed. Annealed films transform into a polycrystalline form containing mixed anatase and rutile phases. For this purpose, devices are annealed at 475°C and observed that their threshold voltage value is 6.5V, subthreshold slope is 0.35 V/dec, Ion/Ioff ratios 2.5×106 and mobility value is 0.672 cm2/V.s. Optical response measurements showed that devices exhibits decent performance at ultraviolet region where TiO2 has band to band absorption mechanism.

ZnO based optical modulator in the visible wavelengths

In order to demonstrate tunable absorption characteristics of ZnO, photodetection properties of ZnO based thin-film transistors are investigated. By controlling the occupancy of the trap states, the optical absorption coefficient of ZnO in the visible light spectrum is actively tuned with gate bias. An order of magnitude change of absorption coefficient is achieved. An optical modulator is proposed exploiting such tunable absorption mechanism.

Plasmonically enhanced hot electron based photovoltaic device: erratum

This erratum amends the missing acknowledgment section in our manuscript. ©2013 Optical Society of America OCIS codes: (040.5350) Photovoltaic; (240.6680) Surface plasmons. References and links 1. F. B. Atar, E. Battal, L. E. Aygun, B. Daglar, M. Bayindir, and A. K. Okyay, “Plasmonically enhanced hot electron based photovoltaic device,” Opt. Express 21(6), 7196–7201 (2013). The acknowledgment text was missing in our published paper [1]. This work was supported in part by European Union Framework Program 7 Marie Curie IRG under Grant 239444, COST NanoTP, The Scientific and Technological Research Council of Turkey-TUBITAK under Grants 109E044, 112M004, and 112E052. #197771

Plasmonic gratings for enhanced near infrared sensitivity of Silicon based Schottky photodetectors

15.00 USD Received 20 Sep 2013; published 24 Sep 2013 (C) 2013 OSA 7 October 2013 | Vol. 21, No. 20 | DOI:10.1364/OE.21.023324 | OPTICS EXPRESS 23324

Triangular metallic gratings for high efficiency thin film solar cells

Schottky photodetectors have been intensively investigated due to their high speeds, low device capacitances, and sensitivity in telecommunication standard bands, in the 0.8μm to 1.5μm wavelength range. Due to extreme cost advantage of Silicon over compound semiconductors, and seamless integration with VLSI circuits, metal-Silicon Schottky photodetectors are attractive low cost alternatives to InGaAs technology1. However, efficiencies of Schottky type photodetectors are limited due to thin absorption region. Previous efforts such as resonant cavities increase the sensitivity using optical techniques, however their integration with VLSI circuits is difficult. Therefore, there is a need for increasing Schottky detector sensitivity, in a VLSI compatible fashion. To address this problem, we design plasmonic grating structures to increase light absorption at the metal-Silicon Schottky interface. There are earlier reports of plasmonic structures to increase Schottky photodetector sensitivity2,, with a renowned interest in the utilization of plasmonic effects to improve the absorption characteristics of metal-semiconductor interfaces3. In this work, we report the design, fabrication and characterization of Gold-Silicon Schottky photodetectors with enhanced absorption in the near infrared region.