Design And Fabrication Of High-performance Optoelectronic Devices In Visible-light Communication

With the increasing demand for mobile data transmission,the shortage of the radio frequency spectrum becomes more and more obvious.Meanwhile,with the rapid development of light-emitting diode?LED?lighting industry,visible light communication?VLC?becomes one of the most promising wireless communication methods.LED with short response time and high-speed modulation characteristics is suitable for light communication systems to achieve the dual functions of lighting and data transmission.VLC,which can be used without spectrum resource licenses and electromagnetic interference has a good research value and application prospect.However,there are still a lot of problems which limit the development of VLC.One of the key problems is how to obtain the high-performance optoelectronic devices which support the high speed VLC well,especially how to improve luminous efficiency and wide bandwidth of LED and how to fabricate detectors which are sensitive to visible light.In this paper,the basic principles of visible light communication and characteristics of LED and detectors were analyzed.In order to optimize the performance of optoelectronic devices,the structures of devices were strictly designed.Further,LED with high efficiency and bandwidth and InGaN visible detectors were improved and fabricated.Performance of LED was enhanced by inserting AlInGaN EBL,and responsivity of InGaN photodetector?PD?was increased by optimizing electrode structure.Finally,the VLC system was designed and realized by high performance optoelectronic devices.The detailed researches of this paper are shown as follow:1.High performance blue LED was achieved by energy band modification on an Al_x In_yGa1-x-yN EBL which is different from the AlGaN EBL in conventional LED.The bandgap,polarization charge,efficiency and luminous were simulated.It is demonstrated that polarization charge density was decreased and the negative effect from polarization electric fields was decreased for the Al_x In_yGa1-x-yN EBL structure with high In/Al ratio Using the optimal In/Al ratio of 0.5,the LED with Al_xIn_yGa1-x-yN EBL shows a comprehensive performance improvement.The fabrication of LED provide the evidence to the superiority of Al_x In_yGa1-x-yN EBL with a high In/Al ratio.Compared with the conventional LED with Al_0.15Ga_0.85N EBL,the light output power,wall-plug efficiency and bandwidth of LED with Al_0.35In_0.175Ga_0.475N EBL were improved by 31%,24%and 10%.2.Compared with APD,PIN,MSM and other types detectors,we simulate the performance of PIN PD and MSM PD.The PIN PD with 1.5?m intrinsic layer gain high responsivity,achieving more than 0.3A/W responsivity on 450nm wavelength and high response speed in the meanwhile.Moreover,the response speed of MSM PD is faster then PIN PD's.MSM PD with high speed sensitivity and planar structure is suitable for fabricating the visible light detector by using InGaN material.InGaN MSM PDs with different interdigital electrode were fabricated after achieving high-quality InGaN,we draw the conclusion that the dark-currents and responsivities increase with the decrease of gap of electrode in this work.InGaN MSM PD with 10?m width electrode and 5?m gap achieve 0.111 A/W responsivity on415nm wavelength and 0.096A/W on 450nm wavelength,which is sensitive to the blue light in VLC.3.The VLC system based with blue LED and visible light photodetector was designed and realized using OFDM technology,and it is shown that the communication system can transmit characters.