High Internal Quantum Efficiency AlGaN Epilayer Grown by Molecular Beam Epitaxy on Si Substrate

We report the molecular beam epitaxy growth and characterization of aluminum gallium nitride (AlGaN) epilayer on an Si substrate. The AlGaN epilayer was grown on an AlN buffer layer through a coalescence process on a nanowire template. The AlGaN epilayer possessed a relatively smooth surface. The room-temperature internal quantum efficiency (IQE) was investigated using power-dependent photoluminescence experiments and theoretical analysis. A maximum IQE of around 50% is derived, with an estimated carrier density of 3 x 10(18) cm(-3). This IQE is significantly improved compared to the previously reported bulk AlGaN epilayers grown on sapphire and/or AlN-on-sapphire templates. The efficiency droop mechanism is also discussed, which could presumably be attributed to the carrier delocalization.