Ultra-violet GaN/Al0.5Ga0.5N quantum dot based light emitting diodes

Abstract

Taking advantage of the strain-induced 2-dimensional (2D)–3D “Stransky–Krastanov type” growth mode of GaN on AlxGa1−xN, we report on the fabrication of ultraviolet (UV) light emitting diodes (LEDs) using GaN quantum dots (QDs) as emitters. The structures have been grown by molecular beam epitaxy on sapphire (0001) substrates. GaN QDs, with density ∼8×1010cm−2, are formed on Al0.5Ga0.5N layers. The electroluminescence (EL) spectrum is dominated by a blue–violet emission (400–430nm) at very low injection currents (≤2A/cm2). At currents above 10A/cm2, a UV emission (<390nm) is observed. An additional peak, at wavelength ∼314nm, originates from the EL emission from the GaN wetting layer. For increasing current, we observe a large shift (∼300meV) towards higher energies and a reduction by one third of the full width at half maximum of the EL peak. Furthermore, the appearance of an additional peak on the EL high energy side is observed. These properties are governed by the quantum confined Stark effect and band-filling in the QDs. AlxGa1−xN-based QD-LED performances (optical power, external quantum efficiency) are presented and discussed in correlation to the specific 3D localization of excitons in the QDs.