EMCCD's are the same as CCD's except that they have an extended "multiplication register (or gain register) please read link below
see here... http://www.photometrics.com/resources/learningzone/onchipmultiplicationgain.php
How can i make my own extended multiplication register and add it to a CCD chip???
As i read it, you cannot do it. I has to happen inside the CCD itself.