Conduction Band and Trap Limited Mobilities in Bi sub 12 Sio sub 20,
UNIVERSITY OF SOUTHERN CALIFORNIA LOS ANGELES
Pagination or Media Count:
The mobility of photoexcited charge carriers in photorefractive insulators can be measured with a holographic time-of-flight technique. By illuminating the crystal with two interfering 30 ps laser pulses at the wavelength of 532 nm, we create an instantaneous sinusoidal pattern of photoexcited charge carriers. A strong electric field E sub 0 is applied across the crystal causing the sinusoidal pattern of charge carriers to drift with a velocity muE sub 0 where mu is the mobility. With a proper choice of the interference fringe spacing alpha, the superposition of this drifting charge pattern on the complementary pattern of photo-ionized traps creates an observable oscillating space charge field. We probe this oscillation by diffracting a weak cw helium-neon beam from the refractive index grating that is created via the electro-optic effect. The period Pt of the observed oscillation is the time required for photoexcited charge carriers to drift over one spatial period A. A time-flight mobility mu can therefore be simply determined using the equation.
- Electricity and Magnetism