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Electrical characterisation of gamma and UV irradiated epitaxial 1.2 kV 4H-SiC PiN diodes
KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
KTH, Superseded Departments, Physics.
2004 (English)In: SILICON CARBIDE AND RELATED MATERIALS 2003, PTS 1 AND 2, 2004, Vol. 457-460, 1487-1490 p.Conference paper, Published paper (Refereed)
Abstract [en]

Epitaxial 4H-SiC 1.2 kV PiN diodes have been evaluated using IN measurement techniques after exposure to 1, 2, 3.8 and 10 Mrad irradiation from the Co-60 gamma source. After accumulated gamma dose of 10 Mrad the diodes were exposed to UV irradiation. The forward and reverse diode characteristics were measured successively in the temperature range from RT to 350 degrees C. The leakage current increases with gamma irradiation dose up to about 4 Mrads by a factor of 20 compared to the pre-irradiation values. After an accumulated dose of 10 Mrads the leakage current decreases by about one order of magnitude but is still about 2-3 times larger than before irradiation. The decrease in reverse current is accompanied by the appearance of the high noise. The apparent thermal activation energies increase with the gamma irradiation dose and show a relatively large spread in values especially at lower temperatures (150 degrees C to 250 degrees C).

The UV irradiation has a positive effect on the IN characteristics. The reverse current is lowered by one order of magnitude compared to the pre-irradiation level. The large noise in the leakage current is absent after UV exposure. The low energy level of 0.2 eV appears clearly in the temperature range between 150 degrees C and 250 degrees C after the UV irradiation. The thermal activation energy of 0.91 eV has been determined for the deep energy level in the temperature range from 250 degrees C to 350 degrees C. The values of the thermal activation energies are very consistent between diodes and show less spread as a function of the applied voltage. The Poole-Frenkel dependence with local field enhancement can be fitted to the 0.91 eV level.

Place, publisher, year, edition, pages
2004. Vol. 457-460, 1487-1490 p.
Series
MATERIALS SCIENCE FORUM, ISSN 0255-5476
Keyword [en]
4H-SiC, Gamma irradiation, UV irradiation, thermal activation energy, PiN diodes
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-6596DOI: 10.4028/www.scientific.net/MSF.457-460.1487ISI: 000222802200354Scopus ID: 2-s2.0-8744310135OAI: oai:DiVA.org:kth-6596DiVA: diva2:11349
Conference
10th International Conferece on Silicon Carbide and Related Materials 2003 (ICSCRM 2003) Lyon, FRANCE, OCT 05-10, 2003
Note

QC 20100928

Available from: 2006-12-12 Created: 2006-12-12 Last updated: 2015-06-17Bibliographically approved
In thesis
1. Characterization of dielectric layers for passivation of 4H-SiC devices
Open this publication in new window or tab >>Characterization of dielectric layers for passivation of 4H-SiC devices
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Silicon carbide rectifiers and MESFET switches are commercially available since 2001 and 2005 respectively. Moreover, three inch SiC wafers can be purchased nowadays without critical defects for the device performance, four inch wafers are available and the next step of technology is set to be the six inch substrate wafers. Despite this tremendous development in SiC technology the reliability issues, like bipolar device degradation, passivation, or low MOSFET channel mobility still remain to be solved.

This thesis focuses on SiC surface passivation and junction termination, a topic which is very important for the utilisation of the full potential of this semiconductor. Five dielectrics with high dielectric constants, Al2O3, AlN, AlON, HfO2 and TiO2 have been investigated. The layers were deposited directly on SiC, or on the thermally oxidized SiC surfaces with several different techniques. The structural and electrical properties of the dielectrics were measured and the best insulating layers were then deposited on fully processed and well characterised 1.2 kV 4H SiC PiN diodes. For the best Al2O3 layers, the leakage current was reduced to half its value and the breakdown voltage was extended by 0.7 kV, reaching 1.6 kV, compared to non passivated devices. Furthermore, AlON deposited on 4H SiC at room temperature provided interface quality comparable to that obtained with the thermally grown SiO2/SiC system.

As important as the proper choice of dielectric material is a proper surface preparation prior to deposition of the insulator. In the thesis two surface treatments were tested, a standard HF termination used in silicon technology and an exposure to UV light from a mercury or deuterium lamp. The second technique is highly interesting since a substantial improvement was observed when UV light was used prior to the dielectric deposition. Moreover, UV light stabilized the surface and reduced the leakage current by a factor of 100 for SiC devices after 10 Mrad γ ray exposition. The experiments show also that the measured leakage currents of the order of pA are dominated by surface leakage.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. xi, 64 p.
Series
Trita-ICT/MAP, 2006:02
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-4229 (URN)978-91-7178-532-9 (ISBN)
Public defence
2006-12-15, Aula N2, KTH-Electrum 3, Isafordsg. 28, Kista, 10:15
Opponent
Supervisors
Note
QC 20100928Available from: 2006-12-12 Created: 2006-12-12 Last updated: 2010-09-28Bibliographically approved
2. Termination and passivation of Silicon Carbide Devices.
Open this publication in new window or tab >>Termination and passivation of Silicon Carbide Devices.
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Silicon carbide rectifiers are commercially available since 2001, and MESFET switches are expected to enter the market within a year. Moreover, three inch SiC wafers can be purchased nowadays without critical defects for the device performance and four inch substrate wafers are announced for the year 2005. Despite this tremendous development in SiC technology, the reliability issues like device degradation or high channel mobility still remain to be solved.

This thesis focuses on SiC surface passivation and termination, a topic which is very important for the utilisation of the full potential of this semiconductor. Three dielectrics with high dielectric constants, Al2O3, AlN and TiO2, were deposited on SiC with different techniques. The structural and electrical properties of the dielectrics were measured and the best insulating layers were then deposited on fully processed and well characterised 1.2 kV 4H SiC PiN diodes. For the best Al2O3 layers, the leakage current was reduced to half its value and the breakdown voltage was extended by 0.5 kV, reaching 1.6 kV, compared to non passivated devices.

As important as the proper choice of dielectric material is a proper surface preparation prior to deposition of the insulator. In the thesis two surface treatments were tested, a standard HF termination used in silicon technology and an exposure to UV light from a mercury lamp. The second technique is highly interesting since a substantial improvement was observed when UV light was used prior to the dielectric deposition. Moreover, UV light stabilized the surface and reduced the leakage current by a factor of 100 for SiC devices after 10 Mrad γ ray exposition. The experiments indicate also that the measured leakage currents of the order of pA are dominated by surface leakage.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. vii, 55 p.
Series
Trita-FTE, ISSN 0284-0545 ; 2005:3
Keyword
Silicon Carbide, SiC, passivation, dielectric materials
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-439 (URN)
Presentation
2005-09-30, C1, KTH-Electrum, Isafjordsgatan 22, Kista, 10:15
Opponent
Supervisors
Note
QC 20110114Available from: 2005-09-29 Created: 2005-09-29 Last updated: 2011-01-14Bibliographically approved

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