Structural analysis of distributed Bragg reflector mirrors

Quantum cascade (QC) lasers and vertical-cavity surface-emitting lasers (VCSELs) are of great interest due to their potential importance for a variety of device applications. Both kinds of lasers call for very highly reflective mirrors. Usually distributed Bragg reflector (DBR) mirrors, which consist of periodic quarter wavelength stacks of high and low refractive index compound semiconductors are used. These stacks are superlattices containing more than 40 individual layers. To obtain very high reflectivity DBRs alternating GaAs and AlAs layers are used for both the high and low index mirrors.GaAs/AlAs DBR structures containing 15 periods were characterized by the complementary use of RBS/channeling, TEM and HRXRD. Since the total thickness of a DBR exceeds 2 μm the RBS analysis was performed at two He-ion energies: 1.7 MeV and 3.82 MeV. After some stopping power corrections TEM and RBS provided similar results. Discrepancies with HRXRD data were attributed to the lateral inhomogeneity of produced superlattice. Virtues and pitfalls of complementary use of these techniques were discussed.