On Wednesday 13 November 2002 14:32, you wrote:

I didn't get anything like that, but the negative voltage generator has a
pronounced threshold as the device starts to avalanche.
I wonder if you are getting an effect caused by the capacitive loading of
the scope probe coupled with, perhaps, a negative resistance region over
the few mV close to avalanche start.  Again a guess.   Steve's memory of
Bob Pease's explanation is a bit unexpected, I wouldn't have thought a
reverse biassed junction would generate light.  After all, LEDs are forward
biassed in operation.

As best I recall the article, the light is visible with a microscope

Steve