QUANTUM CONFINEMENT AND DISORDER IN POROUS SILICON - EFFECTS ON THE OPTICAL AND TRANSPORT-PROPERTIES

The striking optical propel ties of porous silicon (PS) show a twofold aspect typical of an ordered and a disordered material, respectively. Raman, electron microscopy, and resonant photoluminescence studies in dicate that the light emission originates from crystalline regions. On the contrary, several features, like the non-exponential decay of pho toluminescence (PL), the broad emission spectrum, the photoluminescenc e fatigue under light exposure etc. are typical of a disordered materi al and reminiscent of similar effects found e.g. in amorphous semicond uctors. These two apparently conflicting aspects have for a long time hindered the understanding of the basic light emission mechanism. In t his paper we report new optical data showing that disorder in porous s ilicon leads to strong carrier localisation. Light emission in PS is s uggested to occur through transitions involving localized states.