Research On GaN-based Resonant Cavity Light Emitting Diode

GaN-based resonant cavity light-emitting diode(RCLED)is a kind of semiconductor device which combines optical resonant cavity with LED.It is featured by high brightness,narrowband emission,good light output directivity,low manufacturing cost,good temperature stability and so on.Moreover,the light output characteristics of GaN-based RCLED is deeply dependent on the performance of its top reflector.Based on this characteristic,detailed research work on the design of top reflector,fabrication of devices,and performance measurements of GaN-based RCLED have been carried out in this thesis.Two kinds of top reflectors with different structures are designed to optimize the performance of the device.Finally,light emission with single longitudinal mode and tunable wavelength is realized.At the same time,the light output directivity of the device is improved.The main contents of the thesis are as follows:1.Research on GaN-based RCLED with tunable single longitudinal mode light emission.9 pairs of Ta2O5/SiO2 dielectric distributed Bragg reflector(DBR)with filter structure are designed and fabricated.The designed center wavelength of DBR is located at 435nm,451nm,and 461nm respectively,which corresponds to the three resonant longitudinal modes of the cavity.The optical measurements results of the three kinds of devices with different top DBRs show that there is a transparent concave band at the center wavelength in the reflectivity curve of the filter DBR,which plays a good screening effect on the light output wavelength.Single longitudinal mode light emission is achieved for all devices,and the spectral linewidths are all less than 1.3 nm.By changing the center wavelength of the DBR,the emission wavelength of the RCLED device can be effectively adjusted.Eventually,tunable single longitudinal mode light emission is realized in GaN-based RCLED.The emission wavelength is consistent with the light transmission concave band of the filter DBR.Meanwhile,the device shows a good temperature stability.Besides,the photon recycling and reuse phenomenon has been observed in the long-wave device.Due to the light excitation and reuse of the short-wave photons in the device,the long-wave device exhibits higher luminescence efficiency.2.Research on GaN-based RCLED with round-hole structure.A combined reflector composed of a central circular filter DBR and an bordered Ag mirror is designed and fabricated on the surface of the original square device.The measurement results show that the light output of the device mainly concentrates on the top central circular hole and more concentrated in the direction perpendicular to the device.Furthermore,the structure of the combined reflector is optimized.An Ag mirror with circular light-transmitting hole is deposited on the surface of the square filter DBR,which improves the reflectivity of the top reflector on the shading surface.Compared with the RCLED with round-hole structure before optimization,the emission intensity of the optimized device is enhanced,and the temperature stability is improved greatly.This is mainly related to the enhancement of photon recycling and reuse.