Exciton-Photons Interaction In Nitride Semiconductor FP Resonant Cavity

GaN materials are third-generation direct wide-bandgap semiconductor,which have high radiation recombination efficiency and outstanding physical and chemical properties.The tunable band can cover the whole visible region through adjusting the In component.GaN material has been widely used in semiconductor optoelectronic device,especially in the visible light emitting devices.Although GaN-based electrical and optical injection Vertical Surface Emitting Lasers(VCSELs)have been successfully obtained,lasing threshold is still a critical parameter affects the performance of VCSEL.Reducing the lasing threshold is an eternal goal and the exciton polariton is promising candidate for zero threshold lasing.GaN-based semiconductor MCs are considered to be a good candidate for studying the exciton polariton at room temperature due to the following:1)GaN-based semiconductors have relatively large exciton bindingenergy(26meV for bulk GaN,-46meV for quantum wells,QWs)and large exciton oscillator strength,which satisfied theprerequisite for the strong coupling and room temperatureexciton polariton.2)GaN-based semiconductorshave fast relaxation rate,which can effectively suppress the polariton bottleneck effect to benefit polaritons' condensation.However,the large inhomogeneous broadening due to the In composition fluctuation and reduction of oscillator strength caused by QCSE in InGaN QWs were detrimental to the strong coupling.In this thesis,a systematical study on the InGaN cavity consist of double dielectric DBR to study the VCSEL based on the weak coupling and exciton polariton based on strong coupling.The main work is as follows:(1)Cavity principle and structure design:Analyzing and calculating the distribution of electric field and optical confinement factor,cavity mode distributed,reflection characteristics and penetration depth to design the cavity to enhance the interaction strength between excitons and photons.(2)Fabrications and characteristic investigations of low threshold lasing of VCSEL:Increasing the exciton binding energy and oscillator strength by using coupled QWs,which reducing the negative effect of inhomogeneous broadening.Improving bonding,laser lift-off and chemical mechanical polishing(CMP)technique,the double dielectric DBRs cavity with extremely smooth GaN surface was fabricated.The optically pumped VCSEL with the lowest was achieved,which based on weak coupling between exciton and photon.(3)Increasing the coupling strength between exciton and photon by reducing the cavity length:reducing the cavity length to transfer the interaction strength from weak coupling to strong coupling by controlling the pressure in CMP.Angle resolved photoluminescence measurements revealed unambiguous anti-crossing behavior,demonstrating the dispersion relation of exciton polariton.The Rabi splitting can reach the 130meV at the low excitation power.On the other hand,tunable exciton polaritons by continuously varying detuning value were also observed in a wedge-like microcavity.(4)Exciton polariton lasing action:We reported the first polariton lasing in InGaN QWs with double dielectric DBRs cavity by Fourier image angle resolved system at room temperature.Through the intensity mapping,double thresholds corresponding respectively to polariton lasing and photonic lasing were observed dependent on different excitation power.The excitation power reaches the exciton polariton threshold,the nonlinearity of light output was also accompanied by onset of peak blue-shift and linewidth narrowing was observed.The exciton polariton lasing in InGaN QWs,we believe that our results paved a substantial way for the ultra-low threshold visible light laser devices.The results of thesis proved that the effect of inhomogeneous broadening can be reduced by designing the coupled QWs structure and using the high quality cavity,the strong coupling between exciton and photon can be achieved with the 157meV inhomogeneous broadening.The exciton polariton lasing in InGaN quantum wells was observed for the first,which can provide the scientific reference for extremely low threshold visible light laser devices.