Spalling induced van der Waals lift-off and transfer of 4-in. GaN epitaxial films

Abstract

Epitaxial lift-off (ELO) of high-quality GaN layers allows for integration with a variety of materials enabling improved performance, reduced costs, and development of new electronics. Of the ELO technologies, two-dimensional (2D) material-based lift-off offers great promise but is still in the early stages of development and has yet to demonstrate the scale and yield of other ELO technologies. Here, we demonstrate the potential of this process's scalability, speed, and yield through epitaxial growth and lift-off of 4-in. GaN films using a 2D boron nitride (BN) van der Waals (vdW) buffer layer. Since the BN layer acts as the growth template and the mechanical release layer, both the quality and adhesion of the GaN layer are correlated with the BN morphology and uniformity. Detailed spectroscopic mapping demonstrates excellent BN uniformity, which translates into growth of high-quality GaN as shown in mapping of the x-ray rock curves (XRCs), atomic force microscopy, and photoluminescence. Scanning transmission electron microscopy and electron energy loss spectroscopy reveal abrupt chemically distinct interfaces between the sapphire, BN, and AlN/GaN layers essential for efficient lift-off. Combined with the BN/GaN vdW heterostructure, Ni spalling is used to efficiently lift-off and transfer a full 4-in. GaN layer. Post transfer characterization of a 1.9 μm thick GaN layer transferred to a SiO2/Si wafer shows a very minimal change in the XRC and photoluminescence. Strain measurements before and after transfer show that the process fully relaxes residual strain formed in the GaN during high-temperature growth. This work highlights the potential for industry scalability of an exciting 2D material-based lift-off technology, which can facilitate higher power and more efficient radio frequency devices.