Contribution of holes to the photorefractive effect in n-type Bi12SiO20

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Abstract
This is the first characterization of both positive and negative charge carriers as well as deep traps in any crystal sufficient to predict photorefractive behavior for all beam geometries on time scales larger than recombination times. By using beam coupling and light‐induced grating‐erasure measurements, we find the following in a nominally undoped n‐type Bi12SiO20 crystal: (1) the mobility‐lifetime product (7.7±1.3) 10−7 cm2/V for electrons and (1.21±0.34) 10−6 cm2/V for holes; (2) an effective photorefractive trap density of (1.01±0.18) 1016 cm−3; (3) a ratio of absorption coefficients for holes and electrons of 0.242±0.027; and (4) near unity quantum efficiency. The hole contributions to the photorefractive effect in this electron‐dominated crystal are considerable for large grating wave vectors.