Growth and optical characteristics of Tm-doped AlGaN layer grown by organometallic vapor phase epitaxy

We report on the growth and optical properties of Tm-doped AlGaN layers by organometallic vapor phase epitaxy (OMVPE). The morphological and optical properties of Tm-doped GaN (GaN:Tm) and Tm-doped AlGaN (AlGaN:Tm) were investigated by Nomarski differential interference contrast microscopy and photoluminescence (PL) characterization. Nomarski images reveal an increase of surface roughness upon doping Tm into both GaN and AlGaN layers. The PL characterization of GaN:Tm shows emission in the near-infrared range originating from intra-4f shell transitions of Tm³⁺ ions. In contrast, AlGaN:Tm also exhibits blue light emission from Tm³⁺ ions. In that case, the wider band gap of the AlGaN host allows energy transfer to higher states of the Tm³⁺ ions. With time-resolved PL measurements, we could distinguish three types of luminescent sites of Tm³⁺ in the AlGaN:Tm layer, having different decay times. Our results confirm that Tm ions can be doped into GaN and AlGaN by OMVPE, and show potential for the fabrication of novel high-color-purity blue light emitting diodes.