GaN:Pr³⁺ nanostructures for red solid state light emission

Abstract

The photoluminescence of praseodymium implanted and annealed GaN films, quantum wells, nanowires and quantum dots was studied. After implantation and annealing, Pr 3+ intra-shell luminescence was achieved for all the analysed samples. In the trivalent charge state the ions' luminescence was found to be dominated by the red lines of the 3 P 0 / 3 F 2 transition. In the case of GaN films, an intense red emission is observed with the naked eye at room temperature. Photoluminescence excitation indicates that the preferential population mechanisms of this emission are achieved by using excitation above the GaN band gap. A correlation of the optically active ions' luminescence spectral shape and peak position in the different structures is established. For the GaN nanowires the 3 P 0 / 3 F 2 lines of the Pr 3+ ions are in good agreement with those identified in GaN films. In the case of GaN quantum dots, the ions' emission was found to be similar to that observed in AlN layers. For AlN/GaN/AlN quantum wells a similar behaviour was identified with the sharp ionic luminescence lines superimposed as a broad band, likely generated by the overlap of multiple Pr-centres. The ionic luminescence stability was analysed and discussed for all the studied samples.

Incorporation of Europium into GaN Nanowires by Ion Implantation

“…Coexistence of Eu in 2+ and 3+ oxidation states has also been reported for Eu-doped ZnO nanowires63 . In contrast to GaN, in the case of ZnO substitutional Eu is expected to reside in the 2+ charge state but interaction with intrinsic defects allows the stabilization in the 3+64 ,65 .We observe that the Eu 2+ contribution decreases when the fluence is lowered to 5×1014 at/cm and becomes hardly visible for the HTHP annealed reference sample implanted to a fluence of 1×10 14 at/cm 2 , which shows an Eu 2+ fraction of only 16%. A low Eu 2+ fraction of 18% is also seen for NW samples implanted to a fluence as high as 1×1015 at/cm 2 provided they are implanted at 600°C.…”

“…For the case of the doped thin films (Fig. 9b) the intensity first increases with the fluence up to 5×10 14 at/cm and then decreases again due to the severe lattice damage which could not be removed by thermal annealing. This behavior is similar to that observed previously for implantations performed along the c-axis.…”

“…The large shift of the emission to higher energy for the case of the nano-needles can be attributed to surface effects 7 . Confinement effects should play a negligible role in this behavior since only minor shifts due to site multiplicities or different strain states were reported for rare earths incorporated in quantum dots and NWs 13,14 . Sekiguchi et al 9 , reported the Eudoping of GaN NWs during MBE growth leading to similar optical centers as in thin films while exhibiting strongly reduced concentration quenching.…”

Spectroscopic Analysis of Eu3+ Implanted and Annealed GaN Layers and Nanowires

“…18,22 This method is a key technology in the semiconductor industry and allows the introduction of dopants in a controlled way and without the limitations of the solubility of the dopant in the matrix. 23 Previous works from our group 9,24 revealed that it is possible to achieve optical activation of the RE ions in GaN NWs by ion implantation and postimplantation thermal annealing and showed that the emission of the doped NWs, in terms of intensity and thermal stability, is comparable with those obtained for GaN layers processed in similar conditions. 9,24 In the present work different GaN structures (layers and NWs) were doped with Eu 3+ by ion implantation.…”

“…Rare-earth (RE)-doped semiconductors have been widely investigated as a class of materials with promising properties, especially in the optoelectronic area, taking advantage of the remarkable atomic-like intra-4f n transitions of the trivalent charged RE ions. − Gallium nitride (GaN) is a direct wide-bandgap semiconductor with a bandgap energy of 3.4 eV at room temperature . GaN and its ternary alloys are well-established materials in solid-state optics/lighting/optoelectronic applications such as light-emitting diodes (LEDs) and laser diodes (LDs). − Among the main advantages as a host for RE ions, GaN exhibits a high transparency which makes it suitable for the incorporation of the ladder-like RE 3+ electronic energy levels promoting the ion optical activation with reduced luminescence thermal quenching. ,, Furthermore, the 3+ charge state is easily achieved since RE are preferentially on the isovalent Ga site . The large values for both thermal conductivity and breakdown fields provide further benefits for high temperature and high power electronic devices …”