Abstract

We report strong optical diffraction from gratings consisting of alternating regions of high and low carrier concentration. These gratings are prepared by exposing doped III-V compound semiconductors at low temperatures to interfering collimated laser beams. We find a total refractive index shift of 1.3x10^-2 which is 30 times larger than Index shifts found in photorefractive materials such as LiNbO₃. We explain our results quantitatively in terms of the persistent photoconductivity effect (PPG) involving deep donor levels (DX centers) [1,2] coupled with an index shift due to the increased polarizability of free carriers (the plasma effect). The induced gratings can be erased by heating above an annealing temperature determined by the sample composition.

© 1994 Optical Society of America