The arranging structure of the molecular on the surface of P-typed GaN crystal is greatly different from that in the body. The cleaned (0001) surface of the GaN is composed of Ga. The large number of dangling bonds form the surface states. This causes it easy to absorb atoms. The Cs atoms and O atoms are adhere to the surface of the (0001) surface, this will decrease the work function of the GaN, the vacuum energy drops to below zero, until forms the negative electron affinity(NEA). According to semiconductor theory, this will benefit to the escaping of the photoelectron in G-valley when GaN is illuminates with ultraviolet spectrum from 200nm to 380nm. The diagram of energy band structure of the GaN with wurtzite is shown as figure.1.
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