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

• Published in: Science China materials Vol. 66; no. 5; pp. 1978 - 1988
• Main Authors: Zheng, Zhongming, Wang, Yukun, Hoo, Jason, Guo, Shiping, Mei, Yang, Long, Hao, Ying, Leiying, Zheng, Zhiwei, Zhang, Baoping
• Format: Journal Article
• Language: English
• Published: Beijing Science China Press 01.05.2023; Springer Nature B.V
• Subjects: Aluminum gallium nitrides; Chemical-mechanical polishing; Chemistry and Materials Science; Chemistry/Food Science; Dislocation density; Edge dislocations; Epitaxial growth; Material properties; Materials Science; Multi Quantum Wells; Photoluminescence; Quantum efficiency; Radiative recombination; Room temperature; Sapphire; Stimulated emission; Substrates; Superlattices; Ultraviolet radiation; Vertical cavity surface emission lasers; X-ray diffraction; epitaxial lateral overgrowth; UVC; vertical-cavity surface-emitting lasers; laser lift-off; AlGaN
• ISSN: 2095-8226; 2199-4501
• DOI: 10.1007/s40843-022-2310-5

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 10 9 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 ∼10 8 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.