High-quality AlGaN epitaxial structures and realization of UVC vertical-cavity surface-emitting lasers

Abstract

AlGaN-based vertical-cavity surface-emitting lasers (VCSELs) have garnered recent interest due to their superior material properties and device benefits. Nevertheless, AlGaN-based VCSELs are extremely difficult to realize due to numerous technical limitations associated with both material epitaxial growth and chip fabrication. This study fabricated a high-quality AlGaN multiple quantum wells (MQWs) structure using epitaxial lateral overgrowth and analyzed it using X-ray diffraction (XRD) and photoluminescence (PL) measurements. With an edge dislocation density (DD) of 109 cm−2, XRD measurements reveal that the AlN template is nearly fully relaxed. The subsequent AlGaN/AlN superlattice (SL) layer is introduced to decrease the edge DD, and the edge DD in the MQWs is ∼108 cm−2. According to PL measurements, the internal quantum efficiency of the MQWs is as high as 62%, and radiative recombination dominated the emission of the MQWs at room temperature. Using these epitaxial wafers, ultraviolet radiation C (UVC) VCSELs were fabricated using various techniques, including laser lift-off (LLO) and chemical mechanical polishing (CMP). The crystallinity of the MQWs was unaffected by sapphire substrate removal using LLO. After removing the sapphire substrate using LLO and CMP, UVC surface-stimulated emission was observed in MQWs. AlGaN-based UVC VCSELs with lasing wavelengths of 275.91, 276.28, and 277.64 nm have been fabricated. The minimum threshold for UVC VCSELs is 0.79 MW cm−2, which is a record low.