CREATION OF LONG-LIVING ORDERED ELECTRON-HOLE STRUCTURES IN A DISORDERED SYSTEM - SLOW NONLINEAR RESPONSE AND FORMATION OF A BEAM CHANNEL BY WEAK PUMPING

Experimental and theoretical studies of an amorphous As2S5 semiconduct or show the appearance of a nonlinear variation of the refractive inde x DELTAn(e) produced by a weak He-Ne laser beam. The refractive-index variation needs long-time exposure (hours) and survives for a long tim e (a few days) after the laser is switched off. The main feature of th e theoretical model proposed here is the existence of electron and hol e trapped states resulting in slow relaxation and recombination, and t he dependence of generation and recombination rates in a given trap on the space distribution of electron-hole ordering. This dependence res ults in spatial electron-hole ordering: the ordered state is long livi ng and gives a contribution to the refractive-index variation. Some ex perimental results supporting the presented model are also reported.