SOLUTION

• Photo-conductive cells, in which an incident photon removes an electron from the valence band into the conduction band.
• The value of the forbidden energy gap sets a long wave limit to the sensitivity of the photocell.
• A photoconductive cell appears as a linear resistance, which decreases with increased illumination.
• Photo-conductive diodes operate with a reverse voltage of up to 100 V.
• The germanium junction photodiode has a maximum sensitivity of about 30mA/lumen at a light wavelength of 1.6 µ (or 16,000 A).