Negative-resistance effects in light-emitting porous silicon diodes

Definite negative-resistance (NR) effects in electroluminescence(EL)-emissive porous silicon (PS) diodes have been investigated in relation to the EL characteristics. The PS diode is composed of a semitransparent thin Au film, a relatively thin PS layer, a n(+)- or p-type Si substrate and an ohmic back contact. When the forward bias voltage is applied to the diode, a reversible NR behavior is observed in the current-voltage (I-V) characteristics at room temperature. At a low temperature of 10 K, the peak-to-valley current ratio in the n(+)-type substrate case extends to about 10(4). It is shown that the EL emission is switched on at the onset of the NR effect. For the p-type substrate diode, the NR effects can be activated by photoillumination. The mechanism of the observed NR effects is also discussed from the viewpoint of electron injection into the silicon nanocrystallites in PS. The NR effects can be regarded as one of the field-induced functions of PS as a quantum-sized crystalline system.