Comparison of light emitting capacitors with textured and polished silicon substrates towards the understanding of the emission mechanisms

We experimentally compare the optical and electrical characteristics of Light Emitting Capacitors (LECs) using textured and polished silicon surface. The goal of this work is focused to investigate the influence of the roughening of the surface of the silicon substrates in the electro-optical properties of LECs fabricated with off-stoichiometric silicon oxide (SiO_x). The textured surface is produced by reactive ion etching using Ar and SF₆ as ion sources. It exhibits an average roughness of 4.0 ± 0.2 nm, with a spike density of 3.7 ± 1.8 × 10¹⁰ cm⁻². The SiO_x is deposited by low-pressure chemical vapor deposition on polished and textured substrates. The turn-on electric field of LECs using textured substrate is reduced from 8.5 MV/cm to 7.0 MV/cm, and the power conversion is improved 4.1 times compared with LECs with polished substrate. Furthermore, in LECs fabricated over textured substrates, the electrical current value increases at low voltages and once it reaches the high current regime, this value remains constant. Then, the spikes on the silicon substrate improve carrier injection towards the SiO_x at low electric fields, causing more trapping of electrons in the SiO_x and enhancing the electroluminescence response at high electric fields. An explanation of the enhanced electro-emission mechanisms is given. Also, a figure of merit that allows the comparison with LECs with different technological characteristics is proposed.