Research On Integrated Chip Design And Its Key Devices For Visible Light Communication System

Visible light communication is a new high-speed data transmission technology which is based on LED light and “makes it possible to surf the Internet as long as there is light”.It has attracted high attention due to its advantages over conventional radio communication,such as high transmission rate,high transmission safety,zero electromagnetic interference,green,low-carbon and low cost.High quality LED light source and integrated photonic devices are core components for realization of high-speed visible light system.Currently,III-nitride-based LED devices have been commercialized,but there are still some shortcomings such as low luminous efficiency,high power consumption and slow response(modulation bandwidth),which significantly influence the high-speed transmission performance of visible light communication system.Therefore,in order to realize visible light transmission system with high transmission speed and high stability,it is crucial to obtain high-performance LED components which can be integrated and have high light emitting efficiency,low power and high response rate.The purpose of high light emitting efficiency is to reduce the signal to noise ratio(SNR),further increasing the quality of communication.Low power consumption is used to reduce energy consumption and lower the thermal noise of the system,increasing the service life of the system.High response rate is for the improvement of transmission rate and increase communication capacity.The possibility for integration is not only for the increase of the property of LED,the information source but also for the development of visible communication system towards the direction of integration,chip and miniaturization.Now,only a few researchers are engaged in researching and developing high response rate LED components in the world.However,those LED components all use sapphire substrate,and there are few researches on high-performance LED components in the field of visible light communication in China.Recently as the growing technology of GaN-on-Si based LED chip becomes more and more mature,such chips have the advantages of larger size,lower cost,better thermal conductivity and heat stability,compared with GaN-on-sapphire LED chip.Besides,it is easier to integrate such chips,and it is hopeful that the bottleneck which blocks the realization of high-speed data transmission of visible light communication system can be broken.Therefore,this article discusses about the preparation of LED components which can be integrated and have high light emitting ratio,low energy consumption and high response rate by means of using GaN-on-Si based LED chips.Main research contents and results are as follows:1.GaN guided-mode resonance gratings for visible light are designed,fabricated.Meanwhile,the angular resolved micro-reflectance measurement system is built up.Guided-mode resonance grating has modulating function for specific wavelength range and can be used as independent component in visible light communication system to increase the SNR of the system.Meanwhile,it can be integrated with LED as integrating component to increase the information source property of visible communication system.By carrying out analogue simulation for the structural parameter of guided-mode resonance grating,measuring PL(photoluminescence)spectrum,testing the grating performance in the condition of normal incidence,testing the optical property of the grating with using angle-resolved test system,measuring the optical property of grating of various thickness,etc.,the circular grating is observed,of which the period is from nm to 600 nm,duty ratio 0.5 to 0.7 and the height is 130 nm,and linear grating of which the period is 500 nm,550 nm,duty ratio 0.5 to 0.7 and the height is 130 nm.Research results showed that only when incident light match phase conditions,could grating have resonance phenomena.When grating periods are the same,the crest of resonant peak shows blue shift,as duty ratio decreases.When duty ratios are the same,as the period of grating increases,the resonant peak shows red shift,and the reflectivity of grating will significantly increase.When periods and duty ratios are the same,the thinner the GaN film is,the less the resonance models become.Additionally,the resonant peak shows blue shift.The guided-mode resonance gratings have strong effects on incident and reflectance beam,which offer a solution for micro-minimizing the transmitter and receiver of VLC system.2.The suspended film LED components are fabricated by using deep silicon etching process and GaN membrane decreased technology from backside.Suspended film LED is designed for high-performance LED light source with high light-emitting ratio,low energy cost and high response rate in visible light communication system.By using silicon etching technique to peel Si substrate,partial film between the positive electrode and negative electrode of LED chip is suspended.Thinning technology is also adopted for the backside to reduce the thickness of the epitaxial layer of suspended LED,enabling the thickness of LED film to be controllable.Through contrast test,test results of four components,including Si substrate LED,partially suspended film LED and two kinds of suspended film LED with different thickness are collected.Concerning luminous efficiency,thinner LED is obviously better than suspended film LED,and LED with thinner film has better luminous efficiency;while that of suspended film LED is much stronger than Si substrate LED.In terms of power consumption,judging from I-V curve characteristic,thinner LED is obviously better than suspended film LED,but the performance of two kinds of LED with reduced thickness are basically the same concerning power performance,yet suspended film LED is much better than Si substrate LED.About response rate,through C-V curve characteristic it is discovered that when LED is under working pressure,the capacitance characteristics of thinner LED is superior to that of suspended film LED,and the thinner one of the two chips has better performance.Additionally,the suspended film LED is much better than Si substrate LED.Experimental results showed that the performance of LED components with substrate peeling technology and backside reducing technology were much superior to that of traditionally processed LED components.3.The planar propagation mechanism of excitation light is studied.Guided-mode resonance gratings integrated suspended film LED components are designed and fabricated.The excitation light is coupled very well with gratings.The communication in one chip with visible light is realized.The integrated suspended film LED components,of which the p-type light emitting area is totally suspended,are designed to further increase the light emitting ratio and reduce LED power consumption of visible light communication system,enabling the LED to develop towards the direction of integration.This article uses a 325 nm laser device as pump source to observe the leaky modes.The following concludes are reached: when the two conditions of phase-matching condition and quick reduction of optical waveguide mode number are met,leaky film effect will occur.The excitation light of LED can be considered to be made up of two kinds of lights: emergent light vertical to the surface and crosswise emergent light.By using leaky effect,crosswise emergent light spread in LED film can be extracted by using suspended film or guided-mode resonance grating to increase the light emitting efficiency of LED.Meanwhile,the application of leaky film effect provides inspiration for the integration and miniaturization as well as making chips of visible light communication system.