Hexagonal boron nitride (h-BN) can be used as a p-doped material in wide-bandgap optoelectronic heterostructures or as a release layer to allow lift-off of grown three-dimensional (3D) GaN-based devices. To date, there have been no studies of factors that lead to or prevent lift-off and/or spontaneous delamination of layers. Here, we report a unique approach of controlling the adhesion of this layered material, which can result in both desired lift-off layered h-BN and mechanically inseparable robust h-BN layers. This is accomplished by controlling the diffusion of Al atoms into h-BN from AlN buffers grown on h-BN/sapphire. We present evidence of Al diffusion into h-BN for AlN buffers grown at high temperatures compared to conventional-temperature AlN buffers. Further evidence that the Al content in BN controls lift-off is provided by comparison of two alloys, Al 0.03 B 0.97 N/sapphire and Al 0.17 B 0.83 N/sapphire. Moreover, we tested that management of Al diffusion controls the mechanical adhesion of high-electron-mobility transistor (HEMT) devices grown on AlN/h-BN/sapphire. The results extend the control of two-dimensional (2D)/3D hetero-epitaxy and bring h-BN closer to industrial application in optoelectronics.

The mechanical release of III‐nitride devices using h‐BN is a promising approach for heterogeneous integration. Upscaling this technology for industrial level requires solutions that allow a simple pick‐and‐place technique of selected devices for integration while preserving device performance. An advance that satisfies both of these requirements is demonstrated in this work. It is based on a lateral control of the h‐BN quality, using patterned sapphire with a SiO2 mask, to achieve localized van der Waals epitaxy of high‐quality GaN based device structures. After process fabrication, the devices can be individually picked and placed on a foreign substrate without the need for a dicing step. In addition, this approach could reduce delamination of h‐BN on large diameter substrates because each h‐BN region is smaller, with independent device structures. Discrete InGaN LEDs on h‐BN are grown and fabricated on 2 in. patterned sapphire using a SiO2 mask. A set of devices are selectively released and transferred to flexible aluminum tape. The transferred LEDs exhibit blue light emission around 435 nm. The approach presented here is scalable on any wafer size, can be applied to other types of nitride‐based devices, and can be compatible with commercial pick‐and‐place handlers for mass production.

Selective Area van der Waals Epitaxy (SAVWE) of III-Nitride device has been proposed recently by our group as an enabling solution for h-BN-based device transfer. By using a patterned dielectric mask with openings slightly larger than device sizes, pick-and-place of discrete LEDs onto flexible substrates was achieved. A more detailed study is needed to understand the effect of this selective area growth on material quality, device performance and device transfer. Here we present a study performed on two types of LEDs (those grown on h-BN on patterned and unpatterned sapphire) from the epitaxial growth to device performance and thermal dissipation measurements before and after transfer. Millimeter-size LEDs were transferred to aluminum tape and to silicon substrates by van der Waals liquid capillary bonding. It is shown that patterned samples lead to a better material quality as well as improved electrical and optical device performances. In addition, patterned structures allowed for a much better transfer yield to silicon substrates than unpatterned structures. We demonstrate that SAVWE, combined with either transfer processes to soft or rigid substrates, offers an efficient, robust and low-cost heterogenous integration capability of large-size devices to silicon for photonic and electronic applications.

The van der Waals (vdW) epitaxy of three-dimensional (3D) device structures on two-dimensional (2D) layers is particularly interesting for III-nitrides because it may relax lattice matching and thermal mismatch requirements and can allow convenient lift-off of epilayers and optoelectronic devices. In this article, we report the vdW epitaxy of 3D GaN/AlGaN on 2D h-BN grown on a-, c-, and m-plane sapphire substrates via metal–organic chemical vapor phase epitaxy. First, we study 2D h-BN layers grown on a-, c-, and m-plane sapphire to demonstrate the effect of the substrate on h-BN growth and h-BN alignment. We find that h-BN can align itself to its preferred c-axis with a slight misorientation on the m-plane sapphire substrate. However, the differences in crystallographic orientation, thermal expansion coefficient, and surface energy of differently oriented sapphire substrates strongly influence the surface morphology (good for a- and c-planes) and the adhesion of h-BN layers (lift-off only possible for the c-plane). Second, the vdW growth of 3D GaN/AlGaN on 2D h-BN grown on a-, c-, and m-planes of sapphire was investigated. High-resolution X-ray diffraction (HR-XRD) 2θ–ω scan and selected area electron diffraction pattern were used to demonstrate the misorientation of GaN/AlGaN grown on 2D h-BN/m-plane sapphire compared to polar GaN grown on 2D h-BN/a- and c-plane sapphire. It was found that the morphology and crystalline quality of GaN/AlGaN are directly affected by the 2D h-BN layers. These results provide initial insight into the impact of substrate orientation, thereby acting as a guide for the potential design of III-nitride/h-BN vdW epitaxy seeking to use nonpolar or semipolar planes of sapphire for optoelectronic devices such as light-emitting diodes (LEDs), high-power electronics, and detectors.

We demonstrate the fabrication of vertical InGaN light emitting diodes on large-area freestanding membranes, using a mechanical lift-off technique enabled by 2D h-BN. 30-μm-thick electroplated copper deposited on the epilayer (i) gives rigidity to the structure, preventing crack generation, (ii) functions as a back mirror and as a heat sink, and (iii) enables one-step self-lift-off and transfer of LED structures from h-BN/sapphire during a thermal treatment at 100°C. Free-standing arrays of LEDs on thick membranes were processed and their electro-optical performance characterized. This approach can provide a solution for the fabrication of low cost, wafer scale, crack-free, and highly reproducible free-standing arrays of vertical LEDs with up to centimeter-size areas.