Investigation Of GaN-based Resonant-cavity Light-emitting Diodes

GaN materials have been rapidly developed and widely used due to their advantages of wide band gap,high electron drift saturation rate,good themal conductivity and high chemical stability.At present,the research of LED devices is focusing on high brightness,high power,high efficiency and high reliability.GaN-based resonant-cavity]inght-emitting diode(RCLED)has many advantages,such as high brightness,high efficiency,narrow spectral line,high temperature stability,good emission directionality,high bandwidth,low fabrication cost.It has high potential in lighting,sensing and visible light communication applications.RCLED is a good compromise between traditional LED and vertical-cavity surface-emitting laser(VCSEL).With the development of the research on RCLED,device performances have been improved continuously but still need to be improved,due to the particularity of its own structure.Now the research is focusing on how to improve the device efficiency and optical power.In this work,the design,farication,and characterization of GaN-based RCLED were carried out in detail.The main work is as follows:1.Device design and analysis:The concept of resonator and the effect of microcavity are explained in detail.Two important parameters including the Peak intensity enhancement factor(Ge)and the wavelength-integrated intensity enhancement factor(Gint),the relationship between these parameters and the reflectivity of the top and bottom mirrors in the resonator are discussed.Furthermore,the relationship between the enhancement of extraction efficiency and the reflectivity of the two mirrors is calculated theoretically and numerically.2.Device fabrication:The GaN-based RCLEDs are fabricated on a copper substrate by electroplating and laser lift-off techniques.A TiO2/SiO2 dielectric distributed Bragg reflector(DBR)and an aluminum metal reflector were employed as top and bottom mirrors,respectively.In order to further study the effect of top DBR reflectivity on the efficiency and other device characteristics,three kinds of top DBR structures are designed,which are 2 pairs,3 pairs and 3.5 pairs TiO2/SiO2,respectively.3.Performance tests of RCLED devices:As compared to the conventional LED without a top mirror,improved performances were achieved in RCLED devices due to the resonant cavity effect.The effects of the top TiO2/SiO2 dielectric DBR on device characteristics are investigated.By tuning the reflectivity of the top dielectric DBR,the optimum RCLED device with the top DBR reflectivity of 55%shows a high output power of 62 mW,an external quantum efficiency of 14.8%,a full width at half maximum(FWHM)of 12 nm for emission spectrum,a 50%viewing angle of 122°and a-3 dB modulation bandwidth of 48 MHz.The results show that the RCLED device with the optimum reflectors has considerable potential for future high-performance application.