Photoconductivity parameters in lithium niobate

Measurements on a variety of doped (magnesium and/or iron) and undoped lithium niobate crystals in the oxidized state demonstrate an Arrhenius dependence of dark conductivity on reciprocal temperature between 460 and 590 K. All of the crystals had roughly the same conductivity and activation energy (1.21 eV) over the temperature range, implying that all have about the same free‐carrier concentration and mobility. The enhanced photoconductivity of magnesium‐doped lithium niobate is attributed to a greatly reduced trapping cross section of Fe3+ for electrons, the smaller cross section being due to a changed substitutional site for Fe3+. The Fe3+ trapping cross section is calculated from photoconductivity data to be of order 10−18 m2 in undoped lithium niobate. This implies a photoelectron lifetime of order 6×10−11 s in a relatively pure (2‐ppm Fe) oxidized crystal.