AlN/AlGaN Bragg reflectors grown by gas source molecular beam epitaxy

We describe gas source molecular beam epitaxy (GSMBE) of AlN/AlGaN Bragg reflectors (BRs) designed for the spectral region of 250-450 nm. To minimize absorption these structures are grown without GaN layers. BRs described here were grown on sapphire substrates and sapphire substrates with AIN buffers deposited by hydride vapor phase epitaxy (HVPE). The growth mode and surface structure were monitored with reflection high-energy electron diffraction (RHEED). Growth rates and compositions were controlled using in-situ interferometric pyrometry. The BRs described here show excellent reflectivities and are free of cracks over 2 inch diameter wafers.