Design and fabrication of double AlGaN/GaN distributed Bragg reflector stack mirror for the application of GaN-based optoelectronic devices

In this work, a near-ultraviolet (380 nm) double Al_0.2Ga_0.8N/GaN distributed Bragg reflectors (DBRs) stack mirror was designed and fabricated. The double DBRs stack mirror consists of a 30-pair Al_0.2Ga_0.8N/GaN DBRs centered at 375 nm and a 20-pair Al_0.2Ga_0.8N/GaN DBRs centered at 385 nm. Our simulation results show that the method of double DBRs stack mirror design can broaden the stopband width greatly and increase the reflected angle efficiently, compared with the single Al_0.2Ga_0.8N/GaN DBRs mirror. In experiment, the double Al_0.2Ga_0.8N/GaN DBRs stack mirror and the reference Al_0.2Ga_0.8N/GaN DBRs mirror were grown on sapphire substrate by metalorganic chemical vapor deposition. The measured stopband width of the double DBRs stack mirror (~ 25 nm) is more than two times that of the reference DBRs mirror (~ 11 nm), which consists well with our simulation results. It is reasonable to believe that this work could provide a valuable information to obtain AlGaN/GaN DBRs with wide stopband width that can be used in the fabrication of GaN-based resonant cavity light-emitting diodes and vertical cavity surface emitting lasers.