VOLTAGE-TUNABLE PHOTOLUMINESCENCE AND ELECTROLUMINESCENCE OF POROUS SILICON

Experimental results showing two electrically induced phenomena, namel y the voltage-tunable electroluminescence (VTEL) and the voltage-induc ed quenching of porous silicon photoluminescence (QPL) are given. In b oth cases, a spectral shift as large as 300 nm can be recorded for an external bias variation of only 0.5 V. This spectral shift is characte rised by a blue-shift of the whole EL line in the case of the VTEL whe reas it results from a progressive and selective quenching starting by the low-energy part of the luminescence line in the case of the QPL e xperiments. The origin of this spectral shift is discussed in relation with an electrically induced selective carrier injection into the sil icon nanocrystallites accompanied with an enhancement of the non-radia tive recombination taking place by an Auger relaxation process. Finall y, it is shown that a partial oxidation of the porous silicon layer le ads to a complete loss of the selectivity of these two phenomena. This result is qualitatively discussed by considering the voltage drop dis tribution between the substrate and the silicon nanocrystallites. The voltage drops are modified by the growth of the oxide layer on the nan ocrystallite surface leading to a modification of the energy barriers at the crystallite boundaries.