Abstract

The band mobility of electrons (holes) at the bottom of the conduction (valence) band limits the speed per photon and sensitivity of photorefractive materials. Previous experiments in n-type cubic photorefractive Bi₁₂SiO₂₀ (n-bso) have concerned themselves mainly with the measurement of electron mobilities on a time scale of several microseconds after photoexcitation.^1,2 The mobility values obtained in this fashion reflect a trap-limited mobility: the apparent mobility of the charge carriers owing to the combination of trapping and thermal excitation from a level of shallow traps with activation energies of a fraction of an eV. The trap-limited mobility is expected to increase exponentially with temperature and this behavior has been observed.² However, in the first few nanoseconds after excitation the electrons have not yet fallen into a shallow trap, and they move with the characteristic band mobility.¹ Here we measure the band mobility in n- BSO and its temperature dependence by observing the dark diffusion of excited electrons before trapping takes place.³

© 1996 Optical Society of America