Optical studies of strained InGaN/GaN quantum structures implanted with europium for red light emitting diodes

Summary form only given. RE-doped III-nitride semiconductors have attracted much attention as a promising new class of materials that emit light from the RE 4f-shell in the UV, visible and near IR spectral range [1]. Regardless of evident progress in research and technological achievements towards realizing REdoped III-nitride based electroluminescent devices and lasers, one must overcome difficulties in order to make these devices commercially attractive [2,3]. The constant evolution in III-nitride materials growth created an opportunity to investigate the sensitization of the RE³⁺ ions emission when doped in low dimensional layered quantum structures. It was demonstrated that the presence of quantum well (QW) or superlattices (SLs) affect the carrier localization and the radiative emission from incorporated RE³⁺ ions. The internal stress induced in these structures by lattice mismatch between the epilayer containing RE³⁺ ions and substrate or subsequent epilayers provide additional degree of freedom in optimizing energy transfer between a host and optically active RE³⁺ ion center. In this work we investigate the structural properties and luminescence of Eu³⁺ ions implanted to selected InGaN/GaN SL structures. In particular, the In_0.06Ga_0.94N/GaN SL grown by a metal-organic chemical-vapor deposition was studied prior and after implantation. The focus was on the interfaces between the QW layers in implanted structures and resulting luminescence from optically active RE³⁺ ion centers. The structural properties of the In_0.06Ga_0.94N/GaN samples were tested before and after implantation and thermal treatment at temperature up to 950°C in nitrogen ambient. The In_0.06Ga_0.94N/GaN:RE³⁺ SLs have shown a gradual improvement of the multilayer periodicity with increasing the annealing temperature as indicated by the XRD spectra,- and approaching to the original structural quality after annealing at 950°C. It was fund that a compressive stress developed in implanted SLs can be controlled by changing of the annealing conditions. This was experimentally demonstrated by effective tuning of an active quantum well thickness as well as by enhancement of intra-4f-shell transitions intensity from the In_0.06Ga_0.94N/GaN:RE³⁺ SLs. In general, by increasing indium concentration in InxGa_1-xN layer the red shift of the QW emission can be achieved providing opportunity for resonant energy transfer at the expense of expected structural changes related to a larger lattice mismatch between InxGa_1-xN and GaN layers and indium segregation. The strain engineering is an alternative way to tune the emission from the QW without increasing indium content for achieving resonant excitation of Eu³⁺ ion emitting center; however understanding of straininduced polarization in the QW structure is required. Computer simulations have been done to examine the quantum confined Stark effect (QCSE) in studied structures by calculating the internal stress and the strain-induced polarization, which caused the QW emission red shift in In_0.06Ga_0.94N/GaN:Eu³⁺ SLs. The simulated results agreed well with the experimental observations. Finally, we discuss different material engineering approaches for achieving efficient sensitization of emission from Eu³⁺ ions embedded in strain engineered III-Nitride quantum structures suitable for development of red emitting optoelectronic devices.