Structure Optimization And Frequency Characteristics Study Of Resonant-cavity Light Emitting Diodes

Polymer optical fiber has got wide concern of the global optical communicationexperts and related enterprise in the application of the local area network and “fiber-opticinto door”, and gradually has been into the practical stage. Since it is difficult to achievelow-cost lighting source at470nm, which is the PMMA POF’s lowest attenuationwavelength. The lighting source at650nm, which is the second lowest attenuationwavelength, could be the best choice. Resonant cavity light emitting diodes (RCLEDs)have many advantages, such as spectral purity improvement, directionality optimization,output power enhancement, zero threshold, lowcost. RCLEDs could be a goodcompromise in price-performance between semiconductor lasers and semiconductorLEDs, and serve as the best lighting source of PMMA POF communication system.With the deepening research and continuous improvement of the performance, themarket has put forward higher request for RCLEDs on all aspects of performance. Thisdissertation focuses on structure optimization to improve the electrical and opticalproperties of RCLEDs, containing electrode structure and oxide-confined structure, andfocuses on the research of frequency response to improve dynamical property ofRCLEDs, theoretically analyzing intrinsic modulation bandwidth and parasiticparameters on the effect of bandwidth. Main research contents in this dissertation are asfollows：A systematic introduction for RCLED has been made from all aspects, such as theconcept of RCLED, microcavity effect, Purcell effect, the spontaneous radiation of dipolelayer in the medium. Six design priciples for RCLEDs has been stated.According to transmission matrix model of optical thin film theory, the maininfluencing factors on the reflectivity of DBRs has been calculated using MATLAB,containing the pairs and the refractive index difference of DBR. The optical simulation ofreflection spectrum for p-DBR and n-DBR of epitaxial wafers has been maded.Electrode structure optimization was made, and two types of electrode structurewere designed, containing electrode structure A with single ring and electrode structure Bwith double rings. Research on the key technology selective wet oxidation was made, theinfluencing factors on the oxidation rate were discussed, and appropriate oxidationcondition were confirmed by experiment. The oxide-confined RCLEDs with two types ofp-electrode have been fabricated and tested. At20mA and with diameter of emittingaperture80μm, the higher light output power1.228mW was abtained by the RCLEDs with the single ring electrode. At low current, since the influence of heat effect on thedevice performance is not obvious and electrode A has greater light extraction, the lightoutput power of RCLED A is higher than that of B. At high current, as the influence ofheat effect is dominant as compared with light extraction and electrode A has greater heateffect, the light output power of RCLED A is lower than that of B. In conclusion,RCLEDs with the single ring electrode has worse device reliability for great heat effectbut greater light output power at low injected current.With the single ring as electrode, oxide-confined structure optimization was made.Three types of structure devices were successfully made and tested, which were90μm，110μm，and nonoxidation structure. The influence of oxide-aperture on the electrical andoptical properties was analyzed and discussed. The maximum optical power1.909mWwas abtianed by nonoxidation structure RCLEDs. The RCLEDs with samlleroxide-aperture have larger injected current density, greater series resistance resulting inhigher voltage and more Joule heat, and more rapidly reached optical power saturation.The maximum output power of smaller oxide-aperture devices is lower than that of largeroxide-aperture devices. It is because that larger current density and greater seriesresistance could lead to greater Joule heat, which results in more injected electronsrelaxing their energy by the way of nonradiation.Modulation response characteristics were studied. A systematic introduction for theintirnsic modulation response theory and the measures for improving the intirnsicmodulation for RCLEDs were made. Simulation of intirnsic cut-off bandwidth was madefor RCLEDs, the RCLEDs with with samller oxide-aperture had larger intrinsicmodulation bandwidth. The effects of parasitic parameters, which were mianlyoxide-aperture, on the modulation bandwidth were analyzed.