Theory of origins of the photorefractive and photoconductive effects in Bi12SiO20

Abstract

We have observed modulation of the dark current in Bii2Si02c (BSO) as a function of prior irradiation, and a time-varying absorption of radiation that is dependent upon prior irradiation. As a result of these observations and the previously reported observations of photoconductivity, photorefractivity, photosensitivity, and mobility modulation, a model theory of transport has been developed that requires multiple sources of defect/impurity energy levels. A hopping band exists in the forbidden energy gap where these levels coincide. Transport via exchange of charge is possible here, analogous to conduction via hopping in the presence of impurity bands or dense concentrations of defects. Traps capable of containing immobile charge carriers occur where these various levels do not coincide. Large mobility variations can occur as a result of photon-induced modulation of the Fermi level. Much of the phenomena observed in BSO can be explained through interaction between the multiple defect/impurity energy levels.

Influence of photonic excitations on the electrical parameters of TlInS2 crystals

“…Light illumination could also cause a temporary shift in the Fermi level through a rearrangement of the occupation of metastable trapping states, thereby causing a hopping band to appear. In addition to the hopping band generation, hopping band modulation can also occur by incorporating an additional energy level into an existing hopping band, through Fermi level shift [21,22].…”

Dielectric Properties of Bi 12 SiO 20 Crystals Doped by Cr and Mn Ions

“…Note that non-monotoneous change of dark polarising current was observed in undopped BSO crystals [20]. In samples which were in dark over 3 days with shorted electrodes the initial decrease in current was followed by an increase towards a stady-state value which was attained in interval tens of seconds which decreases with the increase of applied field.…”

The growth and photorefractive effect of co‐doped Ce:Cu:BSO crystals

“…The BSO crystal photorefractive effect is shown in Fig.1.It has been reported that typical diffusing length L D is 0.5um and drifting length L P is 10um in 10KV/cm applied electric field [1]. The two length are usually larger than holographic diffraction grating constant, so BSO crystal appears the highest photo-sensitivity in all given crystals up to 300uJ/cm 2 ( wavelength: 514nm; grating constant: 5um) as four times as LiNbO 3 crystal in the same conditions [2,3].…”

“…BSO(Bi 12 SiO 20 ) crystal is one of electro-optic crystals with great photoconductivity and photorefractive effect [1] and belongs to cubic system with the symmetry 23. When BSO is irradiated by modulated light, it will absorb photons to produce photoelectrons which diffuse or drift in applied electric field and are captured by the traps again.…”