Study Of GaN-Based Blue And Green Vertical-Cavity Surface-Emitting Lasers

GaN-based vertical-cavity surface-emitting lasers(VCSELs)offer several advantages,including small volume,circular beam shape and easy to realize single mode lasing,etc.Theoretically,by adjusting the alloy composition of active region,the emission wavelength of GaN-based VCSEL can cover the range from deep ultraviolet to visible regime.After many years of development,room temperature(RT)continuous wave(CW)lasing of current injection GaN-based VCSELs from near ultraviolet to yellow-green regime have been realized.However,there are many problems need to be solved and the performance of VCSEL is still far from practical application.Blue and green GaN-based VCSELs have potential applications in full-color display,medical applications,underwater communication,etc.Therefore,it is of great significance to realize high-performance blue and green VCSELs.This thesis focuses on the study of current injection blue and green VCSEL,including design,fabrication,characterization,and optimization of device,etc.The main work can be summarized as the following aspects:1.VCSEL structural design:The basic device structure and principle of GaN-based VCSEL,the design of distributed Bragg reflector,as well as the mode distribution and gain matching in resonant cavity were analyzed.The key processes for device fabrication were studied.2.Emission dynamics of InGaN quantum well in resonant cavity:Resonant cavity light-emitting diode(RCLED),whose structure is similar with VCSEL,was fabricated.The fabrication and characterization of RCLED provide good foundation for the achievement of high-performance blue and green GaN-based VCSEL.The main work includes the fabrication of RCLED,modeling of carrier dynamic in InGaN quantum well,testing and analysis of time-resolved photoluminescence(TRPL),etc.3.The design,fabrication and test of GaN-based VCSEL emitting in blue and green:Through reasonable design of epitaxial layer structure,inducing the Indium rich localization centers in quantum well combined with cavity effect,green VCSELs based on blue quantum well were realized.The devices showed an output power of 0.2 mW at 50 mA.In addition,by using the quantum dot in quantum well(QD-in-QW)active region,the VCSELs with dual wavelength lasing at 545 nm and 430 nm were achieved,and the threshold current of the device was further reduced significantly.4.Optimization of GaN-based blue and green VCSEL:a SiO2-buried structure was used to form the lateral optical confinement(LOC)in GaN-based VCSEL.RT CW lasing of blue VCSEL(471 nm)was successfully achieved.The experiment results show that the VCSEL with LOC structure has lower threshold current and higher output power compared with the VCSEL without LOC structure.The thermal characteristics of the VCSELs with and without LOC structure were simulated by COMSOL.The optoelectronic characteristics of SiO2-buried structure VCSEL was calculated by PICS3D.All these can be used for reference to optimize the device performance.The main innovations of this thesis are list below:(1)RCLED was fabricated to study the emission dynamics of InGaN quantum well in resonant cavity,which laid a foundation for the fabrication of VCSEL.(2)By inducing Indium rich localization centers in quantum well combined with cavity effect,as well as QD-in-QW active region,CW lasing of current injection blue and green VCSELs were successfully realized at RT.(3)By employing SiO2-buried structure,LOC was formed in current injection VCSEL.The experiment results shown that the LOC structure can effectively reduce internal loss,and thus decrease the threshold current and increase the slope efficiency of the device.(4)Both optical and electrical properties of GaN-based VCSEL with SiO2-buried structure were theoretically investigated by PICS3D.The simulation results showed that the threshold current and slope efficiency of VCSEL were influenced by the thickness of SiO2.