Cubic III‐nitride coupled quantum wells towards unipolar optically pumped lasers

Optical and structural properties of asymmetric coupled cubic-GaN/-AlN quantum wells (QW) are studied. The samples are grown by molecular beam epitaxy on a 50nm c-GaN buffer on 3C-SiC substrate. The active region contains 100 periods of a 2.3nm AlN barrier, a 1.92.1nm silicon doped GaN QW and a 1.01.2nm undoped GaN QW coupled by a 0.91.1nm AlN tunnelling barrier. Phase purity and partial relaxation of the superlattice is observed in reciprocal space maps measured by high resolution X-ray diffraction. Optical properties of coupled QWs are investigated using cathodoluminescence spectroscopy. A clear shift in the emission energy associated with the thickness of the QWs can be observed. Furthermore clear TM-polarized infrared absorption in the 0.550.87eV range is observed at room temperature using Fourier transform infrared spectroscopy. The asymmetric shape of the infrared absorptions reveals the existence of a three level system in the QWs and is explained by contributions of the e1e3 and e2e3 intersubband transitions. Measured transition energies are compared to model calculations using a SchrodingerPoisson solver based on an effective mass model (nextnano3).