What is it called when majority carriers are reduced in a forward conducting diode?

Question

If you lower the current in a diode from say, 1A to .5A (not all the way off) the excess carriers eventually get reduced. What is this process called? recovery? width reduction? How long does this take...transit time? or is it some other phrase?

Answer 1

Well, sort of a simple qualitative description of what happens in a diode is that carriers are injected from a heavily doped region, for example p+, into a more lightly doped region, n-. The carriers diffuse through the depletion region and are swept out of the transition region by the electric field. The carriers in the n- region are mostly holes. When the forward bias is reduced, the level of minority carriers in the n-region must adjust to the new injection level and this takes a finite amount of time. The amount of time it takes depends on how much current is stored in the neutral region and on the lifetime in that region. This is one of the chief considerations for the switching time for switching diodes. I don’t remember a specific name for the change of current other than just a change in minority current injection level. Incidentally, the levels of current that your are describing are more on the order of those for rectifiers. Small signal switching diodes may carry only a few microamperes. When we are discussion switching characteristics we speak of removing the space charge of minority carriers.
Hope this helps some.
FE

Answer 2

The process of minority carrier reduction is called 'recombination' in the majority material. It's usually called 'minority carrier lifetime' within the majority material. The 'transit time' you mentioned is the length of time it takes for a carrier to cross a junction, or the length of time it takes a minority carrier to cross the base region of a bipolar transistor or travel the length of the channel in a FET.

Doug