Regularly arranged Eu-doped GaN nanocolumns grown by RF-plasma-assisted molecular beam epitaxy through Ti-mask selective-area growth technique

Eu-doped GaN (GaN:Eu) is a good candidate for realizing red laser diodes with temperature stability. Nanocolumn crystals are useful for achieving a high optical gain by a high Eu concentration because they can suppress the degradation of crystalline quality. In this study, regularly arranged GaN:Eu or InGaN:Eu/GaN quantum well (QW) nanocolumns were fabricated using the Ti-mask selective-area growth technique by RF-plasma-assisted molecular beam epitaxy. A sharp luminescence corresponding to inner shell electron transition was observed at approximately 620 nm for both the samples. The regular arrangement resulted in a high extinction ratio and uniform emission distribution. Many undesirable nanocrystals observed on the Ti mask due to low-temperature growth of GaN:Eu were easily removed by preparing a SiO2 layer under the Ti mask and lifting it using a HF treatment. The main peaks and emission efficiency of the InGaN:Eu QW nanocolumns depended on the column diameter, with thick nanocolumns (diameters of more than 260 nm) showing a high emission efficiency. These results suggested that regularly arranged GaN:Eu nanocolumns can be one of the basic technologies for the realization of novel optical devices.