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Keywords:

  • cubic III-nitrides;
  • intersubband transitions;
  • molecular beam epitaxy;
  • superlattices

Abstract

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 50 nm c-GaN buffer on 3C-SiC substrate. The active region contains 100 periods of a 2.3 nm AlN barrier, a 1.9–2.1 nm silicon doped GaN QW and a 1.0–1.2 nm undoped GaN QW coupled by a 0.9–1.1 nm 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 0.55–0.87 eV 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 e1–e3 and e2–e3 intersubband transitions. Measured transition energies are compared to model calculations using a Schrödinger–Poisson solver based on an effective mass model (nextnano3).