CCD's and the photoelectric effect Do charge coupled devices as found in telescopes use the photoelectric effect if not what eles librates the electons. Also what is charge intergration in reation to CCD's.
 A: First question:  depends on your definition of photoelectric effect.  In a CCD a photon is absorbed, and the energy given to an electron which is then promoted out of the Fermi sea, just as happens in the traditional experiment of a metal in a vacuum.  However, in a CCD, the electron has only enough energy to get to the conduction band (generates an electron-hole pair), not enough to leave the crystal. This process is sometimes called the photoelectric effect, or internal photoelectric effect.  But one could argue that it is not really the photoelectric effect because no current was generated outside of the crystal.  
Second question:  What happens to those photo-generated electrons?  The microscopic geometry of the CCD is such that there are internal potential barriers that confine them to locations very close to where they were generated (that is, within a pixel). They stay there until the electronics apply voltages to sweep them out.  Before they are swept out, the pixel continues to collect additional photo-generated electrons as long as light is present on the pixel.  So the total number of electrons in a pixel for one exposure is the sum of all the electrons photo-generated during the exposure.  It has integrated the charge.
