Si doping of AlN nanowires grown by plasma assisted molecular beam epitaxy was investigated with the objective of fabricating efficient AlN based deep ultra-violet light-emitting-diodes. The Si concentration ranged from 10 16 to 1.8x10 21 cm -3 . Current-voltage measurements performed on nanowire ensembles revealed an ohmic regime at low bias (below 0.1 V) and a space charge limited regime for higher bias. From temperature dependent current-voltage measurements, the presence of Si donors is evidenced in both shallow and deep DX states with ionization energy of 75 meV and 270 meV respectively. The role of Fermi level pinning on NWs sidewalls is discussed in terms of near surface depletion inducing a favorable formation of shallow Si donors.

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.

Electrical properties of silicon doped AlN nanowires grown by plasma assisted molecular beam epitaxy were investigated by means of temperature dependent current–voltage measurements. Following an Ohmic regime for bias lower than 0.1 V, a transition to a space-charge limited regime occurred for higher bias. This transition appears to change with the doping level and is studied within the framework of the simplified theory of space-charge limited current assisted by traps. For the least doped samples, a single, doping independent trapping behavior is observed. For the most doped samples, an electron trap with an energy level around 150 meV below the conduction band is identified. The density of these traps increases with a Si doping level, consistent with a self-compensation mechanism reported in the literature. The results are in accordance with the presence of Si atoms that have three different configurations: one shallow state and two DX centers.