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    Capacitance analyses of hydrogenated nanocrystalline silicon based thin film transistor
    (Elsevier Science Sa, 2011) Anutgan, Tamila (Aliyeva); Anutgan, Mustafa; Atilgan, Ismail; Katircioglu, Bayram
    The capacitance-voltage (C-V) measurements within 10(6)-10(-2) Hz frequency range were performed on the hydrogenated nanocrystalline silicon (nc-Si:H) bottom-gate thin film transistor (TFT) and metal-insulator-amorphous silicon (MIAS) structure, mechanically isolated from the same TFT. It was found that the conducting thin layer in nc-Si:H film expands the effective capacitor area beyond the electrode in the TFT structure, which complicates its C-V curves. Considering the TFT capacitance-frequency (C-F) curves, the equivalent circuit of the TFT structure was proposed and mechanism for this area expansion was discussed. On the other hand, the MIAS C-F curves were fitted by the equivalent circuit models to deduce its electrical properties. nc-Si:H neutral bulk effect was revealed by the dependence of the MIAS capacitance on frequency within 10(6)-10(3) Hz at both accumulation and depletion regimes. The inversion in MIAS was detected at 10(2)-10(-2) Hz for relatively low negative gate bias without any external activation source. The presence of the ac hopping conductivity in the nc-Si:H film was inferred from the fitting. In addition, the density of the interface traps and its energy distribution were determined. (C) 2011 Elsevier B.V. All rights reserved.
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    Electroformed silicon nitride based light emitting memory device
    (Amer Inst Physics, 2017) Anutgan, Tamila; Anutgan, Mustafa; Atilgan, Ismail; Katircioglu, Bayram
    The resistive memory switching effect of an electroformed nanocrystal silicon nitride thin film light emitting diode (LED) is demonstrated. For this purpose, current-voltage (I-V) characteristics of the diode were systematically scanned, paying particular attention to the sequence of the measurements. It was found that when the voltage polarity was changed from reverse to forward, the previously measured reverse I-V behavior was remembered until some critical forward bias voltage. Beyond this critical voltage, the I-V curve returns to its original state instantaneously, and light emission switches from the OFF state to the ON state. The kinetics of this switching mechanism was studied for different forward bias stresses by measuring the corresponding time at which the switching occurs. Finally, the switching of resistance and light emission states was discussed via energy band structure of the electroformed LED. Published by AIP Publishing.
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    Electroforming of Amorphous Silicon Nitride Heterojunction pin Visible Light Emitter
    (Ieee-Inst Electrical Electronics Engineers Inc, 2011) Anutgan, Mustafa; Anutgan, Tamila; Atilgan, Ismail; Katircioglu, Bayram
    The deposition parameters of doped hydrogenated nanocrystalline silicon grown by plasma-enhanced chemical vapor deposition were scanned to obtain highly conductive films. The optimized p(+) and n(+) nc-Si: H films were used as injecting layers in the fabrication of Si-rich hydrogenated amorphous silicon nitride (a-SiN(x) : H)-based heterojunction p(+) in(+) diode. The as-grown diode was subjected to a Joule-heating-assisted forming process (FP) via the application of a high electric field. The modifications in the luminescent, electrical, and structural properties of the diode subsequent to the FP were investigated. Although the energy distribution of electroluminescence remains almost the same when compared with that of the fresh diode, its intensity is enhanced by at least 30 times with an orange-red emission easily perceived by the naked eye. Parallelly, the low field-current density drastically increases, presumably due to the Si-nanocrystallite formation within the a-SiN(x) : H layer. This formation, triggered by the neighboring nanocrystalline-doped layers, was confirmed by the X-ray diffraction measurements indicating the rise in the local temperature during FP.
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    Optimization of n+ nc-Si:H and a-SiNx:H layers for their application in nc-Si:H TFT
    (Pergamon-Elsevier Science Ltd, 2011) Anutgan, Tamila (Aliyeva); Anutgan, Mustafa; Atilgan, Ismail; Katircioglu, Bayram
    The n-type doped silicon thin films were deposited by plasma enhanced chemical vapor deposition (PECVD) technique at high and low H-2 dilutions. High H-2 dilution resulted in n(+) nanocrystalline silicon films (n(+) nc-Si:H) with the lower resistivity (rho similar to 0.7 Omega cm) compared to that of doped amorphous silicon films (similar to 900 0 cm) grown at low H-2 dilution. The change of the lateral rho of n(+) nc-Si:H films was measured by reducing the film thickness via gradual reactive ion etching. The rho values rise below a critical film thickness, indicating the presence of the disordered and less conductive incubation layer. The 45 nm thick n(+) nc-Si:H films were deposited in the nc-Si:H thin film transistor (TFT) at different RF powers, and the optimum RF power for the lowest resistivity (similar to 92 Omega cm) and incubation layer was determined. On the other hand, several deposition parameters of PECVD grown amorphous silicon nitride (a-SiNx:H) thin films were changed to optimize low leakage current through the TFT gate dielectric. Increase in NH3/SiH4 gas flow ratio was found to improve the insulating property and to change the optical/structural characteristics of a-SiNx:H film. Having lowest leakage currents, two a-SiNx:H films with NH3/SiH4 ratios of similar to 19 and similar to 28 were used as a gate dielectric in nc-Si:H TFTs. The TFT deposited with the NH3/SiH4 similar to 19 ratio showed higher device performance than the TFT containing a-SiNx:H with the NH3/SiH4 28 ratio. This was correlated with the N-H/Si-H bond concentration ratio optimized for the TFT application. (C) 2011 Elsevier Ltd. All rights reserved.
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    Photoluminescence analyses of hydrogenated amorphous silicon nitride thin films
    (Elsevier, 2011) Anutgan, Mustafa; Anutgan, Tamila (Aliyeva); Atilgan, Ismail; Katircioglu, Bayram
    Silicon-rich hydrogenated amorphous silicon nitride (a-SiNx:H) films were grown by plasma enhanced chemical vapor deposition (PECVD) with different r=NH3/SiH4 gas flow ratios. The optical absorption characteristics were analyzed by Fourier transform infrared (FTIR) and UV-visible transmittance spectroscopies. The recombination properties were investigated via photoluminescence (PL) measurements. As r was increased from 2 to 9, the PL emission color could be adjusted from red to blue with the emission intensity high enough to be perceived by naked eye at room temperature. The behaviors of the PL peak energy and the PL band broadness with respect to the optical constants were discussed in the frame of electron-phonon coupling and band tail recombination models. A semiquantitative analysis supported the band tail recombination model, where the recombination was found to be favored when the carriers thermalize to an energy level at which the band tail density of states (DOS) reduces to some fraction of the relevant band edge DOS. For the PL efficiency comparison of the samples with different nitrogen contents, the PL intensity was corrected for the absorbed intensity fraction of the incident PL excitation source. The resulted correlation between the PL efficiency and the subgap absorption tail width further supported the band tail recombination model. (C) 2011 Elsevier B.V. All rights reserved.