Performance Enhancement Of InGaN Detectors By Surface Plasmons

Light Fidelity,i.e.,LiFi,is a new-rising subject proposed by Harald Hass in 2011.Since LiFi has the advantages of environment-friendly,combining lightening and communication,high band width,easy communication web,and high safety,it has become a hot study topic of short-distant wireless communication technology.For now,the communication velocity of LiFi has been up to 1Gbps.Since the detectors is a significant fraction of the LiFi system,suitable detectors for LiFi system has attracted a lot of attentions by the scientists.As for InGaN material system,the band-gap can be smoothly tuned from 3.4 eV to 0.7 eV by changing Indium contents.Therefore the cut-off wavelength of the InGaN detectors can cover the whole visible light region.Additionally,the InGaN detectors have the advantages of small volume,low power consumption,fast response,and low noise.These advantages make InGaN detectors have the potentials in the application of LiFi communication field,and got attached great importance to them.This thesis focuses on the study of performance enhancement of InGaN visible detectors,based on the improvement of InGaN epilayer growth,and the optimizing of the device structures by introducing gain mechanism of localized surface plasmon resonance effect.On one hand,we have systematically studied the large-mismatch epilayer growth model,and given a high-quality GaN buffer layer growth method by the in-situ lateral epitaxy induced by the stress origining from lattice mismatch.After that,we growed InGaN/GaN materials by the period modulation of the growth temperature.On the other hand,we have studied the gain mechanicm of surface plasmon resonance,and put forward an effective method to tune of the dipole resonance wavelengths of surface plasmon resonance generated by the metal nanoparticles.Based on these results,we achieved performance-enhanced InGaN detectors coupled with surface plasmons.The main results are listed as follows:1.We come up with a high-quality ?-nitrides growth method by the in-situ lateral epitaxy induced by the stress origining from lattice mismatch.In order to achieve high-quality InGaN materials,we firstly studied the growth of InGaN materials.Based on the crystal growth theory,in the view of lattice mismatch,we founded the nucleation growth model of mismatch epitaxy.According to the nucleation growth theory of mismatch epitaxy,we adopted the cone model,and simulated the GaN nucleation growth process with various mismatch degrees.The simulation results explain the growth process of hetero-epitaxy under the circumstances of various mismatch degrees.Based on this simulation results,we achieved low-defect-density high-growth-quality GaN buffer layer.Then we further studied the growth kinetics,and the evolution of stress and dislocations.This section helped us to establish the foundation of the growth of high-quality InGaN materials.2.We put forward a method for tuning surface plasmon resonance by controlling the medium around the metal nanoparticles.The surface plasmon resonance wavelength have influence on the performance of the optoelectronic devices.The closer between the resonance wavelength of surface plasmon to the emitting or absorbing light of the optoelectronic devices,the larger that the resonance enhancement factor occurred.Therefore,basing on the Maxwell equation and combining the factors that influence the metal surface plasmon resonance enhancement,we achieved the surface plasmon resonance wavelength tunable from 410 nm to 490 nm.The in-depth study of its mechanism has been done.This work laid a foundation for high performance InGaN detectors.3.Development of surface plasmon enhanced InGaN detector.The fabrication method of the metallic nanoparticles that exciting surface plasmons had been studied.Furthermore,we introduced metallic surface plasmons into InGaN detectors.The fabrication process of the detectors had been optimized.Through testing and analyzing of the performance of the detectors,we obtained high-performance surface plasmon enhanced InGaN detectors.Based on the time domain and frequency domain finite difference method,we simulated the effect of metallic surface plasmon on the performance of the detectors,and revealed the physics machanism of the enhancement of the surface plasmon coupled InGaN detectors.Compared with conventional InGaN detectors,the optimized ones with SiO2/Ag nanostructures have dark-currents of two orders of magnitude lower,and responsivity as high as 0.98 A/W,almost 10 times higher.