If you zap a n-type semicond. with a laser with energy at, say, the band gap, what happens to the donor electrons? For sake of argument, let's say we're at low temp. where the occupation of electrons on donors is high. I know technically, you should only get transitions at the energy of the laser (top of vb to bottom of cb), but do you think that in reality the donor electrons (if shallow enough) would be ripped from their impurity sites? And then 'reattach' after a equilibrating time. Does anyone know what happens?