Asymmetrical Design of AlGaN/GaN Distributed Bragg Reflectors for Near-UV Optoelectronic Applications
Résumé
AlGaN/GaN materials family is one of the best solution to achieve near-UV high reflective Bragg mirrors on GaN substrates. However, the large lattice mismatch occuring between AlGaN and GaN can lead to relaxed structures by the way of cracks which affect the DBR performances. In this work, asymmetrical designs were investigated for the modeling of fully-strained AlGaN/GaN distributed Bragg Reflectors. Such designs should allow to obtain stacks with crack-free surfaces well-adapted for the regrowth of efficient additional monocrystalline layers. First, the critical thickness of MOVPE-grown AlGaN on GaN templates was experimentally determined and modeled. Then, several AlGaN/GaN mirrors with various Al molar fractions and asymmetry factors were simulated demonstrating that non relaxed DBRs could be obtained with adequate parameters. Finally, it has also been shown that there is a best suited Al molar fraction in AlGaN for each DBR centering wavelength.