Localized Surface Plasmons Enhanced Silicon Nitride-based Light-emitting Devices

Silicon opto-interconnection referred to the replacement of electronic devices by silicon photonic devices using existing complementary metal-oxide semiconductor (CMOS) techniques can achieve the higher transmission of information. One of the application difficulties of the silicon opto-interconnection is the fabrication of silicon-based light source with high efficiency, which is also the hotspot of the current research. Silicon nitride film is one of the candidate materials for the silicon-based light source due to its promising luminescence properties, and has attracted an extensive research interest in recent years. However, the external quantum efficiency of silicon nitride based light-emitting devices (SiNx-based LEDs) is still low, which prevent it from being used as the silicon-based light sources. Consequently, much effort have been made on improving the electroluminescence (EL) performance of SiNx-based LEDs.In this thesis, the EL efficiency of SiNx-based LEDs is improved by introducing a silver nanostructures layer into the device structure. Meanwhile, the origin of the EL of SiNx-based LEDs is discussed systematically, from which the tailoring of its EL wavelength is achieved. The primary achievement of this work is described as follow:(1) The origin of the EL of SiNx-based LEDs is discussed systematically by the evolution of the EL peaks and carrier transport mechanism on the injected current/voltage, and the band diagram is also provided. Two EL peaks (P1and P2) together with their blue-shift have been observed in our SiNx-based LEDs. We attribute the peak with shorter wavelength to the recombination of the electrons confined at the K center and the holes located at the band tail formed by=N-. While, the one with longer wavelength is originated from the recombination of the electrons located at conduction band tail and the holes confined in the center of-Si0.(2) A possible coupling mechanism between the localized surface plasmons and excitons in silicon nitride is provided. And the relationship between the Purcell factor and the deposition parameters is investigated in detail, including the average diameter of silver nanostructures, the distance between the metal nanostructures, and the emission wavelength of the luminescence matrix. Finally, the average position of excitons in the silicon nitride is estimated based on the determination of the above relationships. (3) An almost one order of magnitude enhancement of EL efficiency is achieved by the optimization of the sizes of silver nanostrutcures, which is mainly originated from the improvement of the light extraction efficiency (LEE) by the addition of silver nanostructures. For the devices with silver nanostructures onto the silicon nitride, this improved LEE is originated from the surface roughening of ITO electrode by the addition of silver nanostrutcuers. And for the devices with silver nanostructures underneath the silicon nitride, the increased back-scattering by localized surface plasmon resonance also contributes to the improved LEE. Meanwhile, the improvements of internal quantum efficiency and carrier injection efficiency also have an instructive contribution to the improved external quantum efficiency.(4) A possible method on the determination of the main origin of the efficiency droop phenomenon is provided. This phenomenon can be observed in our reference devices, which can be reduced significantly by high-temperature thermal annealing process and/or the addition of silver nanostructures. From the identification of the dominant process contributing to the output power of light as well as the carrier injection conditions for the devices with and without Ag nanostructures, we attributed this phenomenon mainly to the nonradiative Auger recombination. And the overflow of carriers has a negligible contribution on this phenomenon.(5) The tailoring of the EL wavelength of SiNx-based LEDs is achieved by the modulation of the silver nanostructure sizes and/or the injected current/applied voltage. Meanwhile, the wavelength shift of EL peaks and the relative intensity changes of P1peak and P2peak is originated from the weakned localized electrical fields surrounding silver nanostrutuctrues with the increase of silver nanostrutcures. Moreover, the modulation of EL peaks by the size of silver nanoparticles is much more significant than that by injected current.