Browsing by Subject "Hole mobility"

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    Effect of chalcogens on electronic and photophysical properties of vinylene-based diketopyrrolopyrrole copolymers
    (American Chemical Society, 2015) Dhar, J.; Mukhopadhay, T.; Yaacobi-Gross, N.; Anthopoulos, T. D.; Salzner, U.; Swaraj, S.; Patil, S.
    Three vinylene linked diketopyrrolopyrrole based donor−acceptor (D−A) copolymers have been synthesized with phenyl, thienyl, and selenyl units as donors. Optical and electronic properties were investigated with UV−vis absorption spectroscopy, cyclic voltammetry, near edge X-ray absorption spectroscopy, organic field effect transistor (OFET) measurements, and density functional theory (DFT) calculations. Optical and electrochemical band gaps decrease in the order phenyl, thienyl, and selenyl. Only phenyl-based polymers are nonplanar, but the main contributor to the larger band gap is electronic, not structural effects. Thienyl and selenyl polymers exhibit ambipolar charge transport but with higher hole than electron mobility. Experimental and theoretical results predict the selenyl system to have the best transport properties, but OFET measurements prove the thienyl system to be superior with p-channel mobility as high as 0.1 cm2 V−1 s −1.
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    ItemOpen Access
    Enhanced hole transport in InGaN/GaN multiple quantum well light-emitting diodes with a p-type doped quantum barrier
    (Optical Society of America, 2013) Ji Y.; Zhang, Z. -H.; Tan S.T.; Ju, Z. G.; Kyaw, Z.; Hasanov N.; Liu W.; Sun X. W.; Demir, Hilmi Volkan
    We study hole transport behavior of InGaN/GaN light-emitting diodes with the dual wavelength emission method. It is found that at low injection levels, light emission is mainly from quantum wells near p-GaN, indicating that hole transport depth is limited in the active region. Emission from deeper wells only occurs under high current injection. However, with Mg-doped quantum barriers, holes penetrate deeper within the active region even under low injection, increasing the radiative recombination. Moreover, the improved hole transport leads to reduced forward voltage and enhanced light generation. This is also verified by numerical analysis of hole distribution and energy band structure. © 2013 Optical Society of America.
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    Improving hole injection efficiency by manipulating the hole transport mechanism through p-type electron blocking layer engineering
    (Optical Society of America, 2014) Zhang, Zi-Hui; Ju, Z.; Liu W.; Tan S.T.; Ji Y.; Kyaw, Z.; Zhang X.; Hasanov N.; Sun, X. W.; Demir, Hilmi Volkan
    The p-type AlGaN electron blocking layer (EBL) is widely used in InGaN/GaN light-emitting diodes (LEDs) for electron overflow suppression. However, a typical EBL also reduces the hole injection efficiency, because holes have to climb over the energy barrier generated at the p-AlGaN/p-GaN interface before entering the quantum wells. In this work, to address this problem, we report the enhancement of hole injection efficiency by manipulating the hole transport mechanism through insertion of a thin GaN layer of 1 nm into the p-AlGaN EBL and propose an AlGaN/GaN/AlGaN-type EBL outperforming conventional AlGaN EBLs. Here, the position of the inserted thin GaN layer relative to the p-GaN region is found to be the key to enhancing the hole injection efficiency. InGaN/ GaN LEDs with the proposed p-type AlGaN/GaN/AlGaN EBL have demonstrated substantially higher optical output power and external quantum efficiency.