سوال ۱۸ کنکور ارشد مهندسی برق ۱۴۰۴

PASSAGE 2 (paragraph 2):

"In most materials, one absorbed photon generates one electron, but in the case of graphene, one absorbed photon is able to produce many excited electrons, and therefore generate larger electrical signals," explains Koppens. "We have found that this process is very efficient: more than 80% of light energy is converted." Instead of losing excess energy as heat when a photon is absorbed, graphene uses the extra to generate secondary 'hot' electrons. These 'hot' or excited electrons can drive a current, making graphene an alternative material for light harvesting photovoltaic devices or photodetection. The reason for graphene's highly efficient extraction of light energy lies in its unique physical nature. Doped graphene can be thought of as a mixture of a semiconductor, where properties are determined by the behavior of electrons and holes in the conduction and valence bands, and a metal, in which they depend upon the Fermi level.

18- According to paragraph 2, 'hot' electrons «..........» .