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First-principles evolutionary calculation was performed to search for all probable stable Ga–Te compounds at extreme pressure. In addition to the well-known structures of P63/mmc and Fm-3m GaTe and I4/m Ga2Te5, several new structures were uncovered at high pressure, namely, orthorhombic I4/mmm GaTe2 and monoclinic C2/m GaTe3, and all the Ga–Te structures stabilize up to a maximum pressure of 80 GPa. The calculation of the electronic energy band indicated that the high-pressure phases of the Ga–Te system are metallic, whereas the low-pressure phases are semiconductors. The electronic localization functions (ELFs) of the Ga–Te system were also calculated to explore the bond characteristics. The results showed that a covalent bond is formed at low pressure, however, this bond disappears at high pressure, and an ionic bond is formed at extreme pressure. [ABSTRACT FROM AUTHOR]

The photocurrent effect in reverse biased p-n silicon waveguides at wavelength 1550 nm is experimentally investigated. The photocurrent, which is mainly related to surface-state absorption, defect-state absorption and/or two-photon absorption, is more than 0.08 uA/mm under 8 V reverse biasing and 0.75 mW irradiation. The responsivity of a silicon waveguide with length of 4500 um achieves 0.5 mA/W. Moreover, the enhancement of the photocurrent effect under the electric field is discussed. [ABSTRACT FROM AUTHOR]