Tunneling and photoconductivity
Recently a striking new type of photoconductivity based on quantum mechanical tunneling in superlat¬tices has been reported by Capasso et al. The underlying physical cause of this phenomenon is effective mass filtering. Since the tunneling probability of carriers through the barrier layers of a superlattice increases exponentially with decreasing effective mass, electrons are transported through a superlattice much more easily than through the heavy holes. When light is shined on the superlattice, the photogenerated holes essentially remain localized in the wells while the electrons can tunnel through the barriers. Thus the superlattice acts as a filter for effective masses.
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