Kirk Effect - Page 1
Forum section: electronics / projects

author: tree
author_rank: Regular Contributor
timestamp: March 03, 2014, 06:13:23 am
content: Hello folks,I'm trying to understand the Kirk Effect in BJTs. I have read some articles published in IEEE and in my semiconductor device physics textbooks, but they don't offer a good qualitative analysis. The difficulty I'm having is trying to understand how the base widens as a result of high current.So far, I have understood it as far as follows. We'll assume NPN transistors. The base-collector depletion region mostly exists in the collector because of its light doping. When a current is flowing (minority charge carriers, electrons, diffusing from base to collector) there is a constant current density in the depletion region due to velocity limitations. When the current increases, so does the current density in the depletion region and when this current density approaches the doping density of the collector, the depletion region ceases to exist in the collector. I believe that it ceases to exist when the current density approaches the doping density because the ionized donors and the electrons cancel out. Am I correct?A depletion region requires ionized donors and acceptors. Due to the high current density, the ionized donors cease to exist, but what happens to the ionized acceptors which are on the base side of the depletion region?How does the base widen?Thanks for helping me out.

author: tree
author_rank: Regular Contributor
timestamp: March 03, 2014, 02:52:28 pm
content: Quote from: mojo-chan on March 03, 2014, 11:36:17 amWhen you google it, one result links to something about Start Trek.

author: mngiggle
author_rank: Contributor
timestamp: March 03, 2014, 03:53:04 pm
content: I'm not familiar at all with the effect, but one of my textbooks has a bit about it ("The science and engineering of microelectronic fabrication," Stephen A Campbell). To quote: "This effect [base push out or Kirk effect] arises when the density of the minority carriers injected into the base collector depletion region becomes comparable to the doping level in the collector." As to how the base widens, what it says is that the additional carriers compensate for ions in the depletion region, reducing the electric field. When the field approaches zero, the base "begins to encroach in to the metallurgical collector..." So it sounds like you're thinking correctly about it, but it doesn't really give a bunch more info into the mechanism of the base widening.It refers to Kirk's paper, "A theory of Transistor Cutoff Frequency Falloff at Large Current Densities," IRE Trans. Electron Dev., EDL-9:164 (1962).

author: tree
author_rank: Regular Contributor
timestamp: March 03, 2014, 03:59:08 pm
content: I read that paper. My textbook also has a reference. I found another textbook which has a pretty good explanation.It's calledSemiconductor Device Physics and Designby Mishra

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: March 03, 2014, 06:00:27 pm
content: Quote from: tree on March 03, 2014, 02:52:28 pmThis is the *real* Kirk Effect....But in all seriousness, I'm in the middle of reading this online book of Zeghbroeck's. I'll chime back in when I hit that section.

author: calexanian
author_rank: Super Contributor
timestamp: March 04, 2014, 03:24:27 am
content: There are only a few papers brought up in a Google search repeated over and over. Many more results come up for green Orion Slave Girl though....

author: Rory
author_rank: Frequent Contributor
timestamp: March 04, 2014, 04:00:17 am
content: I'm really surprised no-one has mentioned the Spock effect, having to do with FET pinch-off voltages for high currents in Warp fields.

author: vk6zgo
author_rank: Super Contributor
timestamp: March 04, 2014, 09:36:22 am
content: It's Semiconductor theory,Jim,but not as we know it!

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: March 05, 2014, 07:26:49 am
content: tree,I'm sorry. You had a serious question and the peanut gallery (including myself) really derailed your thread. Were you able to find an answer?

author: tree
author_rank: Regular Contributor
timestamp: March 05, 2014, 03:10:30 pm
content: That's alright. It was funny. I tried to find my own explanation and turns out it was correct. I read the explanation in the book I mentioned above. When I have time, I'll try to post the explanation.

author: codeboy2k
author_rank: Super Contributor
timestamp: April 19, 2014, 03:02:22 am
content: Don't forget the Tribble Diode, which exhibits the Tribble effect...

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: April 19, 2014, 04:22:15 am
content: Zombie thread!!!How will this not die?