Tunneling induced electroluminescence from metal-oxide-semiconductor structure on silicon

Silicon is the most important semiconductor material for electronics industry. However, its indirect bandgap makes it hardly emit light, so its applications in optoelectronics are limited. Many efforts had been devoted to converting silicon to light-emitting materials, including porous silicon-based devices, nanocrystalline Si, and so on. In this work, we report electroluminescence on silicon with simple metal-oxide-semiconductor (MOS) structure. The thin oxide is grown by well-controlled rapid thermal oxidation. With extremely thin oxide, significant tunneling current flows through the MOS structure as the metal is properly biased. The tunneled electrons could then occupy the upper energy levels more than the thermal-equilibrium situation. Then luminescence occurs when they have radiative transition to lower energy states. For low biased voltages, the emission occurs around 1150 nm, approximately corresponding to the Si bandgap energy. For large applied voltages, the emission shifts to longer wavelengths and becomes voltage-dependent. MOS structures fabricated on both p-type and n-type silicon exhibit electroluminescence. This is significant because the fabrication of those MOS structures is compatible with CMOS electronics. Therefore, the MOS EL devices provide a particular advantage over other types of luminescence on silicon. The details of the electroluminescence and its physical reason are reported and discussed.