Georgia Tech-CNRS Laboratory

Full 2 inch GaN epilayers were lifted off GaN and c-sapphire substrates by preferential chemical dissolution of sacrificial ZnO underlayers. Modification of the standard epitaxial lift-off (ELO) process by supporting the wax host with a glass substrate proved key in enabling full wafer scale-up. Scanning electron microscopy and x-ray diffraction confirmed that intact epitaxial GaN had been transferred to the glass host. Depth-resolved cathodoluminescence (CL) analysis of the bottom surface of the lifted-off GaN layer revealed strong near-band-edge (3.33 eV) emission indicating a superior optical quality for the GaN which was lifted off the GaN substrate. This modified ELO approach demonstrates that previous theories proposing that wax host curling was necessary to keep the ELO etch channel open do not apply to the GaN/ZnO system. The unprecedented full wafer transfer of epitaxial GaN to an alternative support by ELO offers the perspective of accelerating industrial adoption of the expensive GaN substrate through cost-reducing recycling.

In the last decades, development of the (Al,Ga,In)N materials has led to new generations of opto- and micro-electronic devices. More recently, novel B(Al,Ga,In)N alloys have been proposed for optical applications in the UV range. Since material containing boron possesses unique properties, the B(Al,Ga,In)N materials system is expected to permit the design of improved and/or novel devices. To evaluate this potential, an improved knowledge of the physical properties of these new materials will be required, however. In this work, investigation of optical, structural, and compositional properties of low-boron content BGaN and BAlN ternary and BInGaN quaternary materials grown through Metalorganic Vapor Phase Epitaxy (MOVPE) are presented. It is shown that inclusion of a small amount of boron strongly affects the optical properties allowing the fabrication of BGaN-based Distributed Bragg Reflectors (DBRs) or Distributed Bragg Confinement layers (DBCs) with large refractive index contrast. Indeed, 1% of boron in BGaN/GaN multilayer structures gives a refractive index contrast of more than 0.1, which is equivalent to that of AlGaN/GaN containing 22% aluminum. The potential of boron-based material technology is illustrated for visible range solar cells applications through the example of BInGaN with good crystalline quality grown on ZnO buffered silicon substrates. It was found that through boron introduction, reduced lattice mismatch, and thus reduced tensile strain, could be obtained for high In contents.