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Physical simulation, fabrication and characterization of Wide bandgap semiconductor devices
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2011. , 28 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1492
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-68076Local ID: LIU-TEK-LIC-2011: 31ISBN: 978-91-7393-148-9OAI: oai:DiVA.org:liu-68076DiVA: diva2:416048
Supervisors
Available from: 2011-05-10 Created: 2011-05-10 Last updated: 2011-05-10Bibliographically approved
List of papers
1. Interface state density of free-standing GaN Schottky diodes
Open this publication in new window or tab >>Interface state density of free-standing GaN Schottky diodes
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2010 (English)In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 25, no 9, 095008- p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Iop Publishing Ltd, 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-59253 (URN)10.1088/0268-1242/25/9/095008 (DOI)000281221200009 ()
Available from: 2010-09-10 Created: 2010-09-10 Last updated: 2011-05-10Bibliographically approved
2. Post fabrication annealing effects on electrical and optical characteristics of n-ZnO nanorods/p-Si heterojunction diodes
Open this publication in new window or tab >>Post fabrication annealing effects on electrical and optical characteristics of n-ZnO nanorods/p-Si heterojunction diodes
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

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.

Keyword
heterojunction diodes, ZnO on Si, electrical properties, ZnO nanorods
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-68074 (URN)
Available from: 2011-05-10 Created: 2011-05-10 Last updated: 2014-10-08Bibliographically approved
3. Modeling and simulations of Pd/n-ZnO Schottky diode and its comparison with measurements
Open this publication in new window or tab >>Modeling and simulations of Pd/n-ZnO Schottky diode and its comparison with measurements
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2009 (English)In: Advanced Materials Research, ISSN 1662-8985, Vol. 79-82, 1317-1320 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
ZnO, Schottky contact, Barrier height
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-68075 (URN)10.4028/www.scientific.net/AMR.79-82.1317 (DOI)
Available from: 2011-05-10 Created: 2011-05-10 Last updated: 2014-01-15Bibliographically approved

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