| 1. |
- 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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| 2. |
- Faraz, Sadia Muniza, et al.
(författare)
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Annealing Effects on Electrical and Optical Properties of N-ZnO/P-Si Heterojunction Diodes
- 2011
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Ingår i: <em>Advanced Materials Research Vol. 324 (2011) pp 233-236</em>. - : Trans Tech Publications Inc.. ; , s. 233-236
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Konferensbidrag (refereegranskat)abstract
- The effects of post fabrication annealing on the electrical characteristics of n-ZnO/p-Si heterostructure are studied. The nanorods of ZnO are grown by aqueous chemical growth (ACG) technique on p-Si substrate and ohmic contacts of Al/Pt and Al are made on ZnO and Si. The devices are annealed at 400 and 600 oC in air, oxygen and nitrogen ambient. The characteristics are studied by photoluminescence (PL), current–voltage (I-V) and capacitance - voltage (C-V) measurements. PL spectra indicated higher ultraviolet (UV) to visible emission ratio with a strong peak of near band edge emission (NBE) centered from 375-380 nm and very weak broad deep-level emissions (DLE) centered from 510-580 nm. All diodes show typical non linear rectifying behavior as characterized by I-V measurements. The results indicated that annealing in air and oxygen resulted in better electrical characteristics with a decrease in the reverse current.
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| 3. |
- Faraz, Sadia Muniza, et al.
(författare)
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Electrical Characterization of Si/ZnO Nanorod PN Heterojunction Diode
- 2020
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Ingår i: Advances in Condensed Matter Physics. - : HINDAWI LTD. - 1687-8108 .- 1687-8124. ; 2020
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Tidskriftsartikel (refereegranskat)abstract
- The electrical characterization of p-Silicon (Si) and n-Zinc oxide (ZnO) nanorod heterojunction diode has been performed. ZnO nanorods were grown on p-Silicon substrate by the aqueous chemical growth (ACG) method. The SEM image revealed high density, vertically aligned hexagonal ZnO nanorods with an average height of about 1.2 mu m. Electrical characterization of n-ZnO nanorods/p-Si heterojunction diode was done by current-voltage (I-V), capacitance-voltage (C-V), and conductance-voltage (G-V) measurements at room temperature. The heterojunction exhibited good electrical characteristics with diode-like rectifying behaviour with an ideality factor of 2.7, rectification factor of 52, and barrier height of 0.7 V. Energy band (EB) structure has been studied to investigate the factors responsible for small rectification factor. In order to investigate nonidealities, series resistance and distribution of interface state density (N-SS) below the conduction band (CB) were extracted with the help of I-V and C-V and G-V measurements. The series resistances were found to be 0.70, 0.73, and 0.75 K omega, and density distribution interface states from 8.38 x 10(12) to 5.83 x 10(11) eV(-1) cm(-2) were obtained from 0.01 eV to 0.55 eV below the conduction band.
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| 4. |
- 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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| 5. |
- Muniza Faraz, Sadia, et al.
(författare)
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Modeling and simulations of Pd/n-ZnO Schottky diode and its comparison with measurements
- 2009
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Ingår i: Advanced Materials Research. - 1662-8985. ; 79-82, s. 1317-1320
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Tidskriftsartikel (refereegranskat)abstract
- Modeling of Pd/ZnO Schottky diode has been performed together with a set of simulations to investigate its behavior in current-voltage characteristics. The diode was first fabricated and then the simulations were performed to match the IV curves to investigate the possible defects and their states in the bandgap. The doping concentration measured by capacitancevoltage is 3.4 x 1017 cm-3. The Schottky diode is simulated at room temperature and the effective barrier height is determined from current voltage characteristics both by measurements and simulations and it was found to be 0.68eV. The ideality factor obtained from simulated results is 1.06-2.04 which indicates that the transport mechanism is thermionic. It was found that the recombination current in the depletion region is responsible for deviation of experimental values from the ideal thermionic model deployed by the simulator.
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| 6. |
- Muniza Faraz, Sadia
(författare)
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Physical simulation, fabrication and characterization of Wide bandgap semiconductor devices
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wide band gap semiconductors, Zinc Oxide (ZnO), Gallium Nitride (GaN) and Silicon Carbide (SiC) have been emerged to be the most promising semiconductors for future applications in electronic, optoelectronic and power devices. They offer incredible advantages in terms of their optical properties, DC and microwave frequencies power handling capability, piezoelectric properties in building electromechanical coupled sensors and transducers, biosensors and bright light emission. For producing high quality devices, thermal treatment always plays an important role in improving material structural quality which results in improved electrical and optical properties. Similarly good quality of metal–semiconductor interface, sensitive to the semiconductor surface, is always required.In this thesis we report the study of the interface states density for Pd/Ti/Au Schottky contacts on the free-standing GaN and post fabrication annealing effects on the electrical and optical properties of ZnO/Si hetero-junction diodes. The determination of interface states density (NSS) distribution within the band gap would help in understanding the processes dominating the electrical behavior of the metal–semiconductor contacts. The study of annealing effects on photoluminescence, rectification and ideality factor of ZnO/Si hetero-junction diodes are helpful for optimization and realization to build up the confidence to commercialize devices for lightening. A comparison of device performance between the physical simulations and measured device characteristics has also been carried out for pd/ZnO Schottky diode to understand the behavior of the devices.This research work not only teaches the effective way of device fabrication, but also obtains some beneficial results in aspects of their optical and electrical properties, which builds theoretical and experimental foundation for much better and broader applications of wide band gap semiconductor devices.
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| 7. |
- Muniza Faraz, Sadia, et al.
(författare)
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Post fabrication annealing effects on electrical and optical characteristics of n-ZnO nanorods/p-Si heterojunction diodes
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Annealing effects on optical and electrical properties of n-ZnO/p-Si heterojunction diodes are studied. ZnO nanorods are grown on p-Si substrate by aquous chemical growth technique. As grown samples were annealed at 400 and 600 oC in air, oxygen and nitrogen ambient. Structural, optical and electrical characteristics are studied by Scanning Electron Microscopy (SEM), Photoluminescence (PL), Current–Voltage (I-V) and Capacitance-Voltage (CV) measurements. Well aligned hexagonal–shaped vertical nanorods are revealed in SEM. PL spectra indicated higher ultraviolet to visible emission ratio with a strong peak ofnear band edge emission (NBE) and weak broad deep-level emissions (DLE). For device fabrication Al/Pt non-alloyed ohmic contacts have been evaporated. I-V characteristics indicate that annealing in air and oxygen resulted in better rectifying behavior as well as decrease in reverse leakage current. An improvement in PL intensity has been shown by the samples annealed at 400 oC.
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| 8. |
- Noor, Hadia, et al.
(författare)
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Influence of background concentration induced field on the emission rate signatures of an electron trap in zinc oxide Schottky devices
- 2010
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Ingår i: JOURNAL OF APPLIED PHYSICS. - : American Institute of Physics. - 0021-8979 .- 1089-7550. ; 107:10
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Tidskriftsartikel (refereegranskat)abstract
- Various well-known research groups have reported points defects in bulk zinc oxide (ZnO) [ND (intrinsic): 1014–1017cm−3] naming oxygen vacancy, zinc interstitial, and/or zinc antisite having activation energy in the range of 0.32–0.22 eV below conduction band. The attribution is probably based on activation energy of the level which seems not to be plausible in accordance with Vincent et al., [J. Appl. Phys. 50, 5484 (1979)] who suggested that it was necessary to become vigilant before interpreting the data attained for a carrier trap using capacitance transient measurement of diodes having ND greater than 1015cm−3. Accordingly the influence of background free-carrier concentration, ND induced field on the emission rate signatures of an electron point defect in ZnO Schottky devices has been investigated by means of deep level transient spectroscopy. A number of theoretical models were tried to correlate with the experimental data to ascertain the mechanism. Consequently Poole–Frenkel model based on Coulomb potential was found consistent. Based on these investigations the electron trap was attributed to Zn-related charged impurity. Qualitative measurements like current-voltage and capacitance-voltage measurements were also performed to support the results.
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