Group-III nitrides (III-Ns) based deep ultraviolet photoelectric device have received a wide attention owing to their broad application prospects in the fields of sterilization, polymer curing, biochemical detection, non-line-of-sight communication, and special lighting.[1] Current state-of-the-art commercial III-Ns films are usually hetero-epitaxially grown on large-mismatch substrate by MOCVD. However, the lattice and thermal mismatch between substrate and epilayer that leads to high defect density and especially large biaxial stress, greatly degrade the performance of the III-Ns devices.[2] Recently, the van der Waals epitaxy (vdWE) growth of III-Ns films on graphene (or other two-dimensional materials) has been proposed to reduce the mismatch effect and achieve transferable optoelectronics and electronics.

    In our study, we successfully achieved a strain-free AlN film with low dislocation density through Gr-actuated strain-pre-store engineering and present the mechanism of strain-relaxation in QvdW epitaxy. Combining Raman spectroscopy analysis and first-principles calculations, it is revealed that Gr promotes AlN to pre-store sufficient tensile strain during the coalescence process to compensate for the compressive stress caused by the mismatch during the heteroepitaxial process, thus bringing out a strain-free AlN film (Fig. 1). The as-fabricated 283 nm DUV-LED with Gr exhibits higher LOP compared to its counterpart on bare sapphire (Fig. 2). This work reveals the internal mechanism of QvdW growth of nitride on large-mismatched substrates and undoubtedly sheds light on the further promotion of nitride-based device manufacturing.

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Fig. 1 Characterization of AlN film   Fig. 2 Device properties of DUV-LED

 

Reference

[1] A. Khan, K. Balakrishnan, and T. Katona, Nat. Photonics 2, 77 (2008).

[2] B. H. Le, S. Zhao, X. Liu, S. Y. Woo, G. A. Botton, Z. Mi, Adv. Mater. 28, 8446 (2016).