Influence of the gate and dielectric thickness on the electro-optical performance of SRO-based LECs: Resistive switching, IR and deep UV emission

Abstract

This work presents the charge transport and electroluminescent properties of silicon rich oxide (SRO) films with ~41at% silicon content and different thicknesses (tSRO=24, 53 and 80nm), as dielectric layer in metal-oxide-semiconductor (MOS) capacitive structures. SRO films were thermally annealed at high temperature to induce the silicon nanoparticles (Si-nps) formation. Light emitting capacitors (LECs) with SRO thickness about 80nm behave like a normal MOS structure with a current level at about 10−10 to 10–12A (equipment sensitivity) at low electric fields. However, a high conduction state (HCS) and then a resistance switching (RS) behavior to a low conduction state is observed when the thickness of the SRO film reduces to (and below) 53nm. When the SRO thickness reduces to 24nm, the electric field required to obtain RS behavior increases. The presence of the HCS and RS is related with silicon diffusion from the polysilicon film, used as gate electrode, towards the SRO bulk. The silicon content within the SRO film increases by the Si diffusion as the thickness reduces allowing the formation of preferential conductive paths. Once RS is obtained, LECs emit a broad visible and near infrared (IR) electroluminescence (EL) spectra with several maximum peaks at ~455, 490, 540, 650 and 800nm. For SRO thickness ≥ 53nm, the most intense EL peak is the placed at 650nm. It becomes narrower and stronger when the thickness increases to 80nm as compared to the other ones making a uniform red EL. Nevertheless, when the SRO thickness decreases to 24nm, an additional IR EL peak above 1000nm is observed. This IR band is slightly stronger than that observed at 650nm and results from the silicon substrate emission enhanced by the high current flow through thin SRO films. By other hand, two narrow spectral lines of low intensity in the deep ultraviolet region (253 and 288nm) are observed when the thickness is above 53nm, which are related to the resonant coherent fluorescence effect. The electrical behavior and optical power emission and its relation with the electroluminescent behavior of LECs are analyzed.