Title: Van der Waals epitaxy of nitrides material and deep-UV Light-emitting diodes

Biography:

Zhiqiang liu is the Professor at the Institute of Semiconductors, Chinese Academy of Sciences (IOS, CAS) and the Director of fabrication department at State key lab of solid state lighting.  His research expertise is in building interdisciplinary teams to use compound semiconductor materials and devices for applications in the areas of nitride materials and Light Emitting devices. This research was supported through competitive research grants and contracts through government, industry and others totaling about $4M US as a lead investigator in academia and industry. He has had active collaborations in the US, Europe, and Asia, which has resulted in more than 100 papers, including papers in AM and JACS, APL, Nanoscale.

Abstract

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 further alleviate the self-heating issue, or achieve transferable optoelectronics and electronics. However, the main challenge is that the dangling-bond-free feature of graphene suppresses the III-Ns nucleation, limiting the large-area single-crystalline growth. Here, we successfully grow high quality AlN film on graphene and fabricate DUV-LEDs with a low turn-on voltage, high output power and reliability. Graphene film is directly grown on sapphire substrate to avoid the tedious transfer process and treated in N2 plasma to increase nucleation sites for fast growth of AlN. With the presence of atomic thin graphene film, the substrate still has a weak interaction with the epilayers, insuring growth of large area single-crystalline film with low stress (0.11 GPa) and low dislocation density (1.96 ×108 cm-2), and therefore the as-fabricated LED devices show excellent performance. What’s more, even though nitrides have been successfully grown on Si (111) and reported in many previous reports. Nitride materials grown on Si (100) are of more significant interest to be used in optoelectronic devices intergradation with silicon circuits, which are usually fabricated on Si (100), not (111). In this contribution, we also demonstrated the growth of AlGaN nanowires directly on SiO2/Si (100) substrate using graphene as a buffer layer. This study brings revolutionary technologies for epitaxial growth of nitride film and paves a new pathway for scalable applications of graphene.

Figure1: Guided by the density functional theory, the nucleation of nitride on graphene was shown schematically.