Memory effect in electroformed nanocrystal silicon nitride based thin film LED

In our previous work [1] it was demonstrated that plasma deposited amorphous silicon nitride (a-SiNx:H)-based heterojunction p+in+ diode (Fig.1(a)) was transformed to light emitting diode (LED) after being subjected to... [ view full abstract ]

In our previous work [1] it was demonstrated that plasma deposited amorphous silicon nitride (a-SiNx:H)-based heterojunction p+in+ diode (Fig.1(a)) was transformed to light emitting diode (LED) after being subjected to Joule-heating assisted electroforming. The electroformed LED exhibited stable light emission easily perceived by the naked eye. The electrical transport and electroluminescence mechanisms of this LED were interpreted via a modified band-tail hopping model, taking into account the formation of Si nanocrystals within the i-layer during electroforming [2]. The low plasma deposition temperature (≤ 523 K), low cost and simple production, compatibility with Si technology, long lifetime and applicability on large surfaces of this thin film diode make it a serious potential competitor to the current crystalline and organic LEDs. In this work, we introduce an additional interesting property of this LED - resistive memory switching, thus extending its applications to light emitting memory (LEM). Unlike the previously proposed LEMs in the literature [3], there is no need for integration of two separate devices (light emitter and memory) since this LED itself exhibits the memory effect. Memory phenomenon was observed via systematically scanning current-voltage (I–V) characteristics and paying attention to their sequence and direction (Fig.1(b)). At forward-bias ('forward-1'), the I–V curve is repeatable, independent of scan direction and visible light emission always accompanies. When reverse-bias I–V ('reverse-2') is taken subsequent to 'forward-1', it is similar to the curve 'forward-1' below 1 V. Above 1 V, current density increases ~102 times and then follows 'reverse-3' which becomes normal reverse I–V independent of scan direction. When it is switched to forward bias, the diode remembers its past: 'forward-4' shows almost the same I–V with 'reverse-3' and the visible light emission is absent until ~6 V, where the current density suddenly drops down onto the 'forward-1' and the visible light emission starts. 'Forward-5' reproduces 'forward-1' thus verifying the diode’s return to its original state. The kinetics of switching from light-OFF to light-ON state was studied by applying 3.5–6.5 V forward-voltage stresses and measuring corresponding time when the switching occurs. Finally, these results on memory effect were explained via energy-band diagram of the electroformed LED.