Incorporation of Europium into GaN Nanowires by Ion Implantation

Abstract

Rare earth (RE) doped GaN nanowires (NWs), combining the well-defined and controllable optical emission lines of trivalent RE ions with the high crystalline quality, versatility and small dimension of the NW host, are promising building blocks for future nanoscale devices in optoelectronics and quantum technologies. Europium doping of GaN NWs was performed by ion implantation and structural and optical properties were assessed in comparison to thin film reference samples. Despite some surface degradation for high implantation fluences, the NW core remains of high crystalline quality with lower concentrations of extended defects than observed in ion implanted thin films. Strain introduced by implantation defects is efficiently relaxed in NWs and the measured deformation stays much below that in thin films implanted in the same conditions. Optical activation is achieved for all samples after annealing and, while optical centres are similar in all samples, Eu 3+ emission from NW samples is shown to be less affected by residual implantation damage than for the case of thin films. The incorporation of Eu in GaN NWs was further investigated by nano-cathodoluminescence and X-ray absorption spectroscopy (XAS). Maps of the Eu-emission intensity within a single NW agree well with the Eu-distribution predicted by Monte Carlo simulations suggesting that no pronounced Eu-diffusion takes place. XAS shows that 70-80% of Eu is found in the 3+ charge state while 20-30% is 2+ attributed to residual implantation defects. A similar local environment was found for Eu in NWs and thin films: for low fluences, Eu is mainly incorporated on substitutional Ga-sites while for high fluences XAS points at the formation of a local EuN-like next neighbour structure. Results reveal the high potential of ion implantation as a processing tool at the nano-scale.

Eu3+ optical activation engineering in Al Ga1-N nanowires for red solid-state nano-emitters

“…The incorporation of the rare-earth (RE) trivalent europium ions (Eu 3+ ) into III-N layers [16][17][18][19][20][21][22][23] and nanostructures [24][25][26][27][28][29][30][31][32] was proved as an excellent strategy to obtain red emission characterized by the sharp and stable Eu 3+ intra-4f 6 transitions. This approach was successfully implemented for in situ Eu 3+ -doped GaN-based emitting devices [31,[33][34][35][36][37][38], with Eu 3+ -related luminescence external quantum efficiency (EQE) values reaching ~29% at room temperature (RT) and ~48% at 77 K [39].…”

“…As an alternative to in situ RE incorporation, ex-situ ion implantation constitutes a suitable method to obtain a controlled doping profile with concentration even beyond solubility limits [18,25,26,32,[42][43][44][45][46][47]. This technique requires post-implantation thermal annealing to recover the implantation-induced damage and to optically activate the RE ions.…”

“…To the best of our knowledge, studies on ternary AlxGa1-xN:Eu 3+ over the entire range of AlN content were only performed in layers and revealed a reduced thermal quenching with enhanced Eu 3+ luminescence efficiency for high AlN content hosts [18,51,52]. Besides, Eu 3+ -implantation in III-N NWs can play a key role for improving Eu 3+ luminescence efficiency [26][27][28]: on the one hand, NWs are expected to be less affected by residual implantation-induced damage compared to 2D structures [25]; and on the other hand, Eu 3+ -implantation occurs not only on the upper surface (c-plane) but also on side facets. Although this increases the complexity of implantation damage build-up since crystallographic surface planes can lead to distinct damage in GaN during implantation [53,54], it provides an additional parameter to control the distribution of Eu 3+ and defects within the NW via the implantation geometry [25].…”

“…Besides, Eu 3+ -implantation in III-N NWs can play a key role for improving Eu 3+ luminescence efficiency [26][27][28]: on the one hand, NWs are expected to be less affected by residual implantation-induced damage compared to 2D structures [25]; and on the other hand, Eu 3+ -implantation occurs not only on the upper surface (c-plane) but also on side facets. Although this increases the complexity of implantation damage build-up since crystallographic surface planes can lead to distinct damage in GaN during implantation [53,54], it provides an additional parameter to control the distribution of Eu 3+ and defects within the NW via the implantation geometry [25]. Furthermore, it was shown that the formation of extended defects during ion implantation is reduced for NWs as compared with thin films [25].…”

“…Although this increases the complexity of implantation damage build-up since crystallographic surface planes can lead to distinct damage in GaN during implantation [53,54], it provides an additional parameter to control the distribution of Eu 3+ and defects within the NW via the implantation geometry [25]. Furthermore, it was shown that the formation of extended defects during ion implantation is reduced for NWs as compared with thin films [25].…”