Europium-Implanted AlN Nanowires for Red Light-Emitting Diodes

Europium (Eu)-implanted AlN nanowire (NW) p–n junctions, subjected to rapid thermal annealing at 1000 °C, were investigated in view of application as red light-emitting diodes (LEDs). In a first step, the structural and optical properties of NWs implanted with two different fluences (1 × 1014 cm–2 and 5 × 1014 cm–2) were studied. The luminescence of the trivalent Eu ions (Eu3+) was achieved for both samples using below and above AlN bandgap energy excitation. The excitation below the AlN bandgap occurs through two broad bands, A1 (peaked at ∼270 nm) and A2 (peaked at ∼367 nm), associated with lattice defects. In addition to Eu3+ luminescence, other radiative channels linked to deep-level defects were identified in photoluminescence (PL). The cathodoluminescence (CL) relative intensity ratio between intra-ionic and defect-related emissions increases compared to that of PL. In both PL and CL, the Eu3+ luminescence intensity increases about three times for the highest fluence, while the contribution from radiative recombination at defects decreases. This study also allowed to map an in-depth profile of the optically active Eu3+, revealing that it extends deeper than the range predicted by Monte Carlo simulations. Based on these findings, a proof-of-concept red LED is shown using the NWs implanted with the highest fluence. The devices exhibited the typical rectifying behavior of a p–n junction and an electroluminescence signal dominated by the 5D0 → 7F2 transition (∼624 nm) starting at a threshold voltage of 12 V. The demonstration of red LEDs based on Eu-implanted AlN NWs highlights the potential of such an approach for developing multi-color nano-emitters.