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- Asghar, A. M., et al.
(författare)
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A multiwideband planar monopole antenna for 4G devices
- 2013
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Ingår i: Microwave and Optical Technology Letters. - : Wiley. - 1098-2760 .- 0895-2477. ; 55:3, s. 589-593
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Tidskriftsartikel (refereegranskat)abstract
- This article presents a compact multiband planar antenna designed for mobile phone applications.The antenna performance is achieved by designing a planar monopole antenna into distributed radiating elements. The proposed antenna is comprised of a chopped circular radiator appended with a meander line and an L-strip coupled element, which is an extension of the ground plane. The combination of a chopped circular patch and L-shaped coupling strip residing on the top side generates lower band while upper band resonances are attained separately by chopped circular resonator and meander line elements. The antenna shows a planar structure which occupies an area of 56 x 17.6 mm and can be directly printed onto a circuit board at low cost making it especially suitable for mobile phone applications. The manufactured antenna is experimentally verified and covers several wireless communication bands, such as LTE 750, GSM 850, GSM 900, DCS, UMTS-2110, Bluetooth, WLAN, WiMAX, and UWB. The high frequency structure simulation is used to design and analyze the antenna performance, and a practical structure was fabricated and tested. The measured and simulated return loss show good agreement.
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- Asghar, M., et al.
(författare)
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Characterization of deep acceptor level in as-grown ZnO thin film by molecular beam epitaxy
- 2014
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Ingår i: Chinese Physics B. - : IOP Publishing. - 1674-1056. ; 23:9, s. 097101-
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Tidskriftsartikel (refereegranskat)abstract
- We report deep level transient spectroscopy results from ZnO layers grown on silicon by molecular beam epitaxy (MBE). The hot probe measurements reveal mixed conductivity in the as-grown ZnO layers, and the current-voltage (I-V) measurements demonstrate a good quality p-type Schottky device. A new deep acceptor level is observed in the ZnO layer having activation energy of 0.49 +/- 0.03 eV and capture cross-section of 8.57 +/- 10(-18) cm(2). Based on the results from Raman spectroscopy, photoluminescence, and secondary ion mass spectroscopy (SIMS) of the ZnO layer, the observed acceptor trap level is tentatively attributed to a nitrogen-zinc vacancy complex in ZnO.
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- Ashraf, H., et al.
(författare)
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Study of electric field enhanced emission rates of an electron trap in n-type GaN grown by hydride vapor phase epitaxy
- 2010
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Ingår i: Journal of Applied Physics. - : American Institute of Physics. - 0021-8979 .- 1089-7550. ; 108:10
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Tidskriftsartikel (refereegranskat)abstract
- Electric field-enhanced emission of electrons from a deep level defect in GaN grown by hydride vapor phase epitaxy has been studied. Using the field dependent mode of conventional deep level transient spectroscopy (DLTS), several frequency scans were performed keeping applied electric field (12.8-31.4 MV/m) and sample temperature (300-360 K) constant. Arrhenius plots of the resultant data yielded an activation energy of the electron trap E ranging from E-c -0.48 +/- 0.02 eV to E-c-0.35 +/- 0.02 eV, respectively. The extrapolation of the as-measured field dependent data (activation energy) revealed the zero-field emission energy (pure thermal activation energy) of the trap to be 0.55 +/- 0.02 eV. Various theoretical models were applied to justify the field-enhanced emission of the carriers from the trap. Eventually it was found that the Poole-Frenkel model associated with a square well potential of radius r=4.8 nm was consistent with the experimental data, and, as a result, the trap is attributed to a charged impurity. Earlier, qualitative measurements like current-voltage (I-V) and capacitance-voltage (C-V) measurements were performed, and screening parameters of the device were extracted to ascertain the reliability of DLTS data.
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- Muniza Faraz, Sadia, et al.
(författare)
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Interface state density of free-standing GaN Schottky diodes
- 2010
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Ingår i: Semiconductor Science and Technology. - : Iop Publishing Ltd. - 0268-1242 .- 1361-6641. ; 25:9, s. 095008-
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Tidskriftsartikel (refereegranskat)abstract
- Schottky diodes were fabricated on the HVPE-grown, free-standing gallium nitride (GaN) layers of n- and p-types. Both contacts (ohmic and Schottky) were deposited on the top surface using Al/Ti and Pd/Ti/Au, respectively. The Schottky diode fabricated on n-GaN exhibited double barriers with values of 0.9 and 0.6 eV and better performance in the rectification factor together with reverse and forward currents with an ideality factor of 1.8. The barrier height for the p-GaN Schottky diode is 0.6 eV with an ideality factor of 4.16. From the capacitance-voltage (C-V) measurement, the net doping concentration of n-GaN is 4 x 10(17) cm(-3), resulting in a lower reverse breakdown of around -12 V. The interface state density (N-SS) as a function of E-C-E-SS is found to be in the range 4.23 x 10(12)-3.87 x 10(11) eV(-1) cm(-2) (below the conduction band) from Ec-0.90 to E-C-0.99. Possible reasons responsible for the low barrier height and high ideality factor have been addressed.
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- Asghar, M., et al.
(författare)
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Characterization of deep level defects in sublimation grown p-type 6H-SiC epilayers by deep level transient spectroscopy
- 2012
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Ingår i: Physica B: Condensed Matter. - : Elsevier. - 0921-4526.
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Konferensbidrag (refereegranskat)abstract
- In this study deep level transient spectroscopy has been performed on boron-nitrogen co-doped 6H-SiC epilayers exhibiting p-type conductivity with free carrier concentration (N-A-N-D)similar to 3 x 10(17) cm(-3). We observed a hole H-1 majority carrier and an electron E-1 minority carrier traps in the device having activation energies E-nu + 0.24 eV, E-c -0.41 eV, respectively. The capture cross-section and trap concentration of H-1 and E-1 levels were found to be (5 x 10(-19) cm(2), 2 x 10(15) cm(-3)) and (1.6 x 10(-16) cm(2), 3 x 10(15) cm(-3)), respectively. Owing to the background involvement of aluminum in growth reactor and comparison of the obtained data with the literature, the H-1 defect was identified as aluminum acceptor. A reasonable justification has been given to correlate the E-1 defect to a nitrogen donor.
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- Asghar, M., et al.
(författare)
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Study of deep level defects in doped and semi-insulating n-6H-SiC epilayers grown by sublimation method
- 2012
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Ingår i: Physica B: Condensed Matter. - : Elsevier. - 0921-4526.
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Konferensbidrag (refereegranskat)abstract
- Deep level transient spectroscopy (DLTS) is employed to study deep level defects in n-6H-SiC (silicon carbide) epilayers grown by the sublimation method. To study the deep level defects in n-6H-SiC, we used as-grown, nitrogen doped and nitrogen-boron co-doped samples represented as ELS-1, ELS-11 and ELS-131 having net (N-D-N-A) similar to 2.0 x 10(12) cm(-3), 2 x 10(16) cm(-3) and 9 x 10(15) cm(3), respectively. The DLTS measurements performed on ELS-1 and ELS-11 samples revealed three electron trap defects (A, B and C) having activation energies E-c - 0.39 eV, E-c - 0.67 eV and E-c - 0.91 eV, respectively. While DLTS spectra due to sample ELS-131 displayed only A level. This observation indicates that levels B and C in ELS-131 are compensated by boron and/or nitrogen-boron complex. A comparison with the published data revealed A, B and C to be E-1/E-2, Z(1)/Z(2) and R levels, respectively.
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| 10. |
- Buonomo, Antonio, et al.
(författare)
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A CMOS Injection-Locked Frequency Divider Optimized for Divide-by-Two and Divide-by-Three Operation
- 2013
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Ingår i: IEEE Transactions on Circuits and Systems Part 1. - : Institute of Electrical and Electronics Engineers (IEEE). - 1549-8328 .- 1558-0806. ; 60:12, s. 3126-3135
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Tidskriftsartikel (refereegranskat)abstract
- This paper proposes a simple and effective modification of the conventional divide-by-two injection locked frequency divider (ILFD) with direct-injection aimed at allowing both the divide-by-two and the divide-by-three modes of operation. The proposed circuit does not employ additional inductors as usual in divide-by-three ILFDs, but exploits the combined effect of two independent injection techniques. The resulting locking range for the divide-by-three mode is comparable in size to that for the divide-by-two. Thus, the proposed circuit can be an optimum alternative to existing dividers, due to the flexibility of two division ratios and due to the absence of additional inductors. An intuitive explanation of the locking mechanism underlying this ILFD and a quantitative analysis are provided, allowing one to predict the amplitude and phase of oscillation in the locked mode, as well as the locking range, with approximate closed-form expressions. Measurements on a circuit prototype and results from SPICE simulations demonstrate the effectiveness of the circuit and validate the theoretical model and the resulting formulas.
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