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

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 ∼8×1010 cm−2, are formed on Al0.5Ga0.5N layers. The electroluminescence (EL) spectrum is dominated by a blue–violet emission (400–430 nm) at very low injection currents (≤2 A/cm2). At currents above 10 A/cm2, a UV emission (<390 nm) is observed. An additional peak, at wavelength ∼314 nm, originates from the EL emission from the GaN wetting layer. For increasing current, we observe a large shift (∼300 meV) 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.

► AlGaN-based UV light emitting diodes using quantum dots as emitters are fabricated.
► Quantum dots are grown by using the epitaxial strain between GaN and AlxGa1−xN.
► UV electroluminescence peaks from the dots and the wetting layer are observed.
► Quantum confined Stark effect and band-filling in the quantum dots are studied.
► LEDs performances related to the specific 3D localization of excitons are analyzed.