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Dynamic avalanche in Si and 4H-SiC power diodes
KTH, Superseded Departments, Electronics.
1999 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Semiconductor power modules for the control of high currentsand high voltages have important applications in motor drives,traction and power transmission. Dynamic avalanche is of atechnological interest since it may limit the safe operatingarea for bipolar switching devices and for power diodes, whichare important integral parts of a power module. Dynamicavalanche is caused by a current-controlled space charge, whichmay enhance the electric field to the critical field strengthat voltages below the static breakdown voltage. Measurementsand simulations of reverse recovery at high power densitieswere performed for Si and 4H-SiC p+nn+power diodes to investigate the failure limitcaused by dynamic avalanche. A special optical measurementtechnique was used to eliminate influence of the junction edgeand thereby probe the bulk diode area.

It was found experimentally that it is possible for Si powerdiodes to sustain dynamic avalanche at very high powerdensities (>1MW/cm2) during reverse recovery. It is proposed thatthese diodes eventually fail as a result of impact ionizationat the diode nn+junction, which according to device simulations,results in current filamentation and an excessive localizedheating. No temperature dependence was found for the failurelimit and similar results were obtained for diodes with andwithout carrier lifetime control. The high failure limitmeasured with the optical technique correlates with a very gooddynamic ruggedness in conventional electrical reverse recoverymeasurements. Device simulations indicate that a deep n+profile may improve the diode failure limit.

A low failure limit close to the onset of dynamic avalanchewas found for another Si power diode, which had a structuredp-zone with a lowly doped p profile extending to the metalcontact in a fraction of the active area. A suggested failurecause for this diode is punch-through of a high electric fieldthrough the p region to the metal contact, an effect which maybe enhanced by an inhomogeneous current resulting from dynamicavalanche.

Some of the investigated 4H-SiC p+nn+diodes showed no dynamic reduction of thebreakdown voltage in reverse recovery measurements. The highpredicted onset level of dynamic avalanche for 4H-SiC couldhowever not be reached, since breakdown at the junction edgelimited the static breakdown voltage to between 800 and 1200 V.A similarly processed test diode showed a clear avalanche inthe bulk during reverse recovery at 300 V, even though thediodes could block more than 2 kV in static measurements. Basedon device simulation, it is proposed that this largediscrepancy between static and dynamic breakdown voltage iscaused by temporary trapping of holes in deep donor levelswhich enhance the space charge and thus the peak electricfield. Deep hole traps were found in the vicinity of the pnjunction by DLTS measurements.

Keywords:dynamic avalanche, power diode, failure limit,dynamic ruggedness, avalanche injection, silicon, siliconcarbide, impact ionization

Place, publisher, year, edition, pages
Stockholm: KTH , 1999. , 74 p.
Series
Trita-EKT, ISSN 1650-8599 ; 9903
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-2815ISBN: 99-2969374-2 OAI: oai:DiVA.org:kth-2815DiVA: diva2:8537
Public defence
1999-06-04, 00:00 (English)
Note
QC 20100527Available from: 2000-01-01 Created: 2000-01-01 Last updated: 2010-05-27Bibliographically approved
List of papers
1. Avalanche injection in high voltage Si PiN diodes
Open this publication in new window or tab >>Avalanche injection in high voltage Si PiN diodes
1997 (English)In: Physica scripta. T, ISSN 0281-1847, Vol. T69, 134-137 p.Article in journal (Refereed) Published
Abstract [en]

An experimental technique using optical excitation by a YAG laser pulse for studying avalanche injection in power devices is demonstrated This technique enables the creation of high uniform excess carrier concentrations in an optically defined device volume, involving very little heating. A method for determining the onset of avalanche multiplication, by studying the time integral of the reverse recovery current, is proposed. A PiN diode is observed to turn off from avalanching at a dissipated power density of more than 200 kW/cm(2).

Keyword
THYRISTORS, DEVICES
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-13085 (URN)A1997WL40600024 ()
Note
QC 20100527Available from: 2010-05-27 Created: 2010-05-27 Last updated: 2017-12-12Bibliographically approved
2. Avalanche Injection in High Voltage Si P-i-N Diodes Measurements and Device Simulations
Open this publication in new window or tab >>Avalanche Injection in High Voltage Si P-i-N Diodes Measurements and Device Simulations
1997 (English)In: ISPSD '97: Proceedings of the International Symposium on Power Semiconductor Devices and ICs, 1997, 125- p.Conference paper, Published paper (Other academic)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-13086 (URN)0-7803-3994-0 (ISBN)0-7803-3993-2 (ISBN)0-7803-3995-9 (ISBN)
Conference
[9th] International Symposium on Power Semiconductor Devices and ICs, Weimar, Germany, May 26-29, 1997
Note
QC 20100527 Available from: 2010-05-27 Created: 2010-05-27 Last updated: 2010-05-27Bibliographically approved
3. Reverse Recovery and Avalance Injection in High Voltage SiC PIN Diodes
Open this publication in new window or tab >>Reverse Recovery and Avalance Injection in High Voltage SiC PIN Diodes
1998 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 264-268, 1041- p.Article in journal (Other academic) Published
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-13087 (URN)
Note
QC 20100527Available from: 2010-05-27 Created: 2010-05-27 Last updated: 2017-12-12Bibliographically approved
4. Dynamic avalanche in 3.3-kV Si power diodes
Open this publication in new window or tab >>Dynamic avalanche in 3.3-kV Si power diodes
Show others...
1999 (English)In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 46, no 4, 781-786 p.Article in journal (Refereed) Published
Abstract [en]

Measurements of the safe reverse recovery limit were performed for 3.3-kV Si power diodes using a novel optical experimental technique. In this experiment, influence of the junction termination is effectively eliminated by optical generation of a laterally-localized carrier plasma. The turn-off failures observed in measurements at two temperatures showed no temperature dependence and could not be reproduced in ordinary one-dimensional (1-D) or two-dimensional (2-D) device simulations. To simulate the stability of the current density toward current filamentation, two 1-D diodes with an area ratio 1:19 and a 10% difference in initial carrier plasma level, were simulated in parallel. This resulted in a strongly inhomogeneous current distribution, and a rapid reverse voltage fall resembling the measured turn-off failures. Inhomogeneous current distribution in these simulations appears as the current decay ceases due to impact ionization, in qualitative agreement with a current instability condition proposed by Wachutka [1].

Keyword
dynamic avalanche, impact ionization, power diode, reverse recovery, SOA, turn-off failure
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-13088 (URN)10.1109/16.753714 (DOI)000079394700024 ()
Note
QC 20100527Available from: 2010-05-27 Created: 2010-05-27 Last updated: 2017-12-12Bibliographically approved
5. Stable dynamic avalanche in Si power diodes
Open this publication in new window or tab >>Stable dynamic avalanche in Si power diodes
1999 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 74, no 21, 3170-3172 p.Article in journal (Refereed) Published
Abstract [en]

A stable dynamic avalanche at a maximum power density of about 2.4 MW/cm(2) was measured in small areas of 3.3 kV Si power diodes, using an optical measurement technique, and very good dynamic ruggedness was verified in a conventional turn-off measurement. Device simulations of a diode with a shallow n(+) emitter indicate that impact ionization at the nn(+) junction can result in negative differential resistance (NDR) and current filamentation, whereas a deep n(+) emitter in the experimentally studied diode suppresses NDR. It is, therefore, proposed that the deep n(+) emitter is important for the stable dynamic avalanche.

Keyword
TRANSISTORS
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-13089 (URN)10.1063/1.124097 (DOI)000080467500031 ()
Note
QC 20100527Available from: 2010-05-27 Created: 2010-05-27 Last updated: 2017-12-12Bibliographically approved
6. Dynamic avalanche in Si power diodes and impact ionization at the nn(+) junction
Open this publication in new window or tab >>Dynamic avalanche in Si power diodes and impact ionization at the nn(+) junction
2000 (English)In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 44, no 3, 477-485 p.Article in journal (Refereed) Published
Abstract [en]

The reverse recovery failure limit was measured with an optical technique for power diodes which sustain high levels of dynamic avalanche. Measurements and simulations indicate that these diodes withstand dynamic avalanche at the pn-junction and eventually fail as a result of a strongly inhomogeneous current distribution caused by the onset of impact ionisation at the diode nn(+) junction - a mechanism similar to the reverse bias second breakdown of bipolar transistors.

Keyword
TURN-OFF, TRANSISTORS, THYRISTORS, INJECTION
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-13090 (URN)10.1016/S0038-1101(99)00261-0 (DOI)000085469300012 ()
Note
QC 20100527Available from: 2010-05-27 Created: 2010-05-27 Last updated: 2017-12-12Bibliographically approved
7. Dynamic avalanche and trapped charge in 4H-SiC diodes
Open this publication in new window or tab >>Dynamic avalanche and trapped charge in 4H-SiC diodes
Show others...
2000 (English)In: SILICON CARBIDE AND RELATED MATERIALS: 1999 PTS, 1 & 2 / [ed] Carter CH; Devaty RP; Rohrer GS, 2000, Vol. 338-3, 1327-1330 p.Chapter in book (Other academic)
Abstract [en]

A dynamically reduced breakdown voltage from more than 2 kV under static conditions to 300 V during reverse recovery was measured for 4H-SiC p(+)nn(+) diodes. Device simulation indicates that deep hole-trapping donors in the n-base, close the pn junction, could explain the dynamically reduced breakdown voltage. Hole traps situated 0.66 eV above the valence band were found in the diode n-base by DLTS measurements.

Series
MATERIALS SCIENCE FORUM, ISSN 0255-5476 ; 338-3
Keyword
carrier traps, dynamic avalanche, impact ionization, reverse recovery, DEEP, CENTERS, DEVICES
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-13091 (URN)000165996700323 ()
Note
QC 20100527Available from: 2010-05-27 Created: 2010-05-27 Last updated: 2010-05-27Bibliographically approved

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