An investigation was made of the defect characteristics of single-crys
tal Bi12SiO20 (BSO) grown by both Czochralski (Cz) and hydrothermal tr
ansport methods. Only Cz-grown BSO is photorefracting using a coherent
pumping source centered around 500 nm, as undoped hydrothermal BSO is
transparent throughout the visible spectrum. Thermally stimulated cur
rent (TSC) studies in conjunction with temperature-dependent optical-a
bsorption measurements and room-temperature photoconductivity data all
indicate that the hydrothermal material is near intrinsic in terms of
its low defect content. TSC measurements made below room temperature
indicate that concentrations of traps of activation energy <0.7 eV are
a factor of 10(3) smaller in hydrothermal than in Cz BSO. At least si
x different defects were identified in the TSC measurements. Temperatu
re-dependent optical-absorption measurements indicate two Urbach band
tails for Cz-grown materials that are not observed in the hydrothermal
materials. Cz material of lower purity also possesses an impurity ban
d tail which can be observed through temperature dependent optical abs
orption measurements. Comparison of Cz material with hydrothermal BSO
of similar impurity content suggests that the Bi(Si) defect responsibl
e for the 500 nm absorption may be complexed with an impurity such as
Fe or V. In the absence of this defect, however, these impurities have
no effect on the absorption. An additional defect in the TSC data is
also related to a transition metal impurity. The results indicate that
the photoconductivity associated with the photorefractive effect in C
z material must proceed via a trap-hopping conduction mechanism that i
s missing in the intrinsic material.