Shallow donor and DX state in Si doped AlN nanowires grown by molecular beam epitaxy

Si doping of AlN nanowires (NWs) 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 1016 to 1.8 × 1021 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 an ionization energy of 75 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.