Browsing by Subject "Electric Fields"

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    Comparative study of field-dependent carrier dynamics and emission kinetics of InGaN/GaN light-emitting diodes grown on (11 2-2) semipolar versus (0001) polar planes
    (AIP Publishing, 2014) Ji Y.; Liu W.; Erdem, T.; Chen R.; Tan S.T.; Zhang Z.-H.; Ju, Z.; Zhang X.; Sun, H.; Sun, X. W.; Zhao Y.; DenBaars, S. P.; Nakamura, S.; Demir, Hilmi Volkan
    The characteristics of electroluminescence (EL) and photoluminescence (PL) emission from GaN light-emitting diodes (LEDs) grown on (11 (2) over bar2) semipolar plane and (0001) polar plane have been comparatively investigated. Through different bias-dependent shifting trends observed from the PL and time-resolved PL spectra (TRPL) for the two types of LEDs, the carrier dynamics within the multiple quantum wells (MQWs) region is systematically analyzed and the distinct field-dependent emission kinetics are revealed. Moreover, the polarization induced internal electric field has been deduced for each of the LEDs. The relatively stable emission behavior observed in the semipolar LED is attributed to the smaller polarization induced internal electric field. The study provides meaningful insight for the design of quantum well (QW) structures with high radiative recombination rates.
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    Enhanced memory effect with embedded graphene nanoplatelets in ZnO charge trapping layer
    (AIP Publishing, 2014) El Atab, B.; Cimen, F.; Alkis, S.; Okyay, Ali Kemal; Nayfeh, A.
    A charge trapping memory with graphene nanoplatelets embedded in atomic layer deposited ZnO (GNIZ) is demonstrated. The memory shows a large threshold voltage Vt shift (4 V) at low operating voltage (6/-6 V), good retention (>10 yr), and good endurance characteristic (>104 cycles). This memory performance is compared to control devices with graphene nanoplatelets (or ZnO) and a thicker tunnel oxide. These structures showed a reduced Vt shift and retention characteristic. The GNIZ structure allows for scaling down the tunnel oxide thickness along with improving the memory window and retention of data. The larger Vt shift indicates that the ZnO adds available trap states and enhances the emission and retention of charges. The charge emission mechanism in the memory structures with graphene nanoplatelets at an electric field E ¥ 5.57 MV/cm is found to be based on Fowler-Nordheim tunneling. The fabrication of this memory device is compatible with current semiconductor processing, therefore, has great potential in low-cost nano-memory applications. © 2014 AIP Publishing LLC.
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    Nanoplasmonic surfaces enabling strong surface-normal electric field enhancement
    (Optical Society of America, 2013) Gungor, K.; Unal, E.; Demir, Hilmi Volkan
    Conventional two-dimensional (2D) plasmonic arrays provide electric field intensity enhancement in the plane, typically with a surface coverage around 50% in the plan-view. Here, we show nanoplasmonic three-dimensional (3D) surfaces with 100% surface coverage enabling strong surface-normal field enhancement. Experimental measurements are found to agree well with the full electromagnetic solution. Along with the surface-normal localization when using the plasmonic 3D-surface, observed maximum field enhancement is 7.2-fold stronger in the 3D-surface than that of the 2D counterpart structure. 3D-plasmonic nonplanar surfaces provide the ability to generate volumetric field enhancement, possibly useful for enhanced plasmonic coupling and interactions. © 2013 Optical Society of America.
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    On the origin of the electron blocking effect by an n-type AlGaN electron blocking layer
    (AIP Publishing, 2014) Zhang Z.-H.; Ji Y.; Liu W.; Tan S.T.; Kyaw, Z.; Ju, Z.; Zhang X.; Hasanov N.; Lu S.; Zhang, Y.; Zhu B.; Sun, X. W.; Demir, Hilmi Volkan
    In this work, the origin of electron blocking effect of n-type Al 0.25Ga0.75N electron blocking layer (EBL) for c+ InGaN/GaN light-emitting diodes has been investigated through dual-wavelength emission method. It is found that the strong polarization induced electric field within the n-EBL reduces the thermal velocity and correspondingly the mean free path of the hot electrons. As a result, the electron capture efficiency of the multiple quantum wells is enhanced, which significantly reduces the electron overflow from the active region and increases the radiative recombination rate with holes. © 2014 AIP Publishing LLC.
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    Simultaneous phase matching of optical parametric oscillation and second harmonic generation in a periodically-poled lithium niobate
    (OSA Publishing, 2003-02) Kartaloglu, T.; Figen, Z. G.; Aytur, O.
    We report a simple ad hoc method for designing an aperiodic grating structure to quasi-phase match two arbitrary second-order nonlinear processes simultaneously within the same electric-field-poled crystal. This method also allows the relative strength of the two processes to be adjusted freely, thereby enabling maximization of the overall conversion efficiency. We also report an experiment that is based on an aperiodically poled lithium niobate crystal that was designed by use of our method. In this crystal, parametric oscillation and second-harmonic generation are simultaneously phase matched for upconversion of a femtosecond Ti:sapphire laser to 570 nm. This self-doubling optical parametric oscillator provides an experimental verification of our design method. © 2003 Optical Society of America