Search

The growth of hexagonal boron nitride (h‐BN) and van der Waals (vdW) epitaxy of blue multi‐quantum well (MQW) GaN‐based LED heterostructures on 6‐inch sapphire substrates using metal‐organic chemical vapour deposition (MOCVD) is demonstrated. Challenges associated with the growth of large surface h‐BN and the subsequent vdW epitaxy of GaN‐based LED heterostructures are discussed. To overcome these challenges, the spatial uniformity is controlled of the growth temperature, optimizes the slope of temperature variations during the growth and cooling process, and manages the surface temperature during switching of gas flows. With these adaptations, high quality GaN‐based LED heterostructures are grown on h‐BN without any spontaneous delamination. The GaN‐based LED devices are then fabricated on a 6‐inch sapphire wafer, which are lifted off as a membrane and transferred to a flexible copper support. These GaN‐based LED devices emitt bright blue illumination with an electroluminescence peak at 437 nm. This scaling up of growth, lift‐off, and transfer can lead to the commercialization of GaN‐based LEDs on h‐BN template on 6‐inch sapphire substrates, with a process compatible with current modern equipment for the fabrication of LEDs and electronic devices. [ABSTRACT FROM AUTHOR]

Several technological challenges have prevented GaN‐based micro‐LEDs from finding application in mass market displays, despite their unique properties such as very high brightness and the very fast response time of GaN‐based materials. The primary challenges are the cost and complexity of lift‐off and transfer of LEDs from sapphire substrates to suitable supports as well as the lowered performance of tiny micro‐LEDs caused by chemical etching that defines individual LEDs. Herein, this work reports demonstration of a complete process that solves these challenges with epitaxy and cleanroom technologies that are commercially available. The process begins with van der Waals epitaxy of 2D h‐BN on silica masks with square, triangular and hexagonal patterns on sapphire substrates which define the micro‐LED regions. Then selective area growth of MQW LED heterostructures, with ultra smooth crystalline sidewalls, down to ultra tiny size of 1.4 µm is performed. Because of the lack of vertical chemical bonds in the h‐BN layer, simple mechanical lift‐off and transfer is performed on an array of LEDs heterostructures down to size of 8 µm. Finally, transparent ITO p‐contacts are deposited on LEDs with uniform lift‐off, resulting in high brightness LEDs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Highlights from the article: Keywords: 2D boron nitride; core/shell nanostructures; flexible electronics; nanorods; semiconductors; van der Waals epitaxy In article number 1900207, Suresh Sundaram, Abdallah Ougazzaden, and co-workers demonstrate self-organized GaN nanorods formation on layered h-BN templates by van der Waals epitaxial growth. Nanorods, semiconductors, flexible electronics, core/shell nanostructures, van der Waals epitaxy, 2D boron nitride.

Hexagonal boron nitride (h‐BN) is a promising 2D template that decouples substrate effects from the layer above it by van der Waals epitaxy, because there are only weak forces out of the h‐BN. It also permits convenient mechanical transfer of devices grown on their surface to an appropriate substrate. Here, van der Waals epitaxial growth resulting in the formation of self‐organized GaN nanorods on h‐BN templates is demonstrated. This approach to the growth of III‐N nanostructures avoids transfer processes and scaling issues seen with other 2D materials, since both the 1D (GaN nanorods) and 2D (h‐BN) are grown at the wafer‐scale and in one growth run. Further, this process is used to grow vertical core–shell p‐GaN/InGaN/n‐GaN nano‐PIN device structures on wafer‐scale 2D h‐BN on sapphire and silicon substrates. The high quality of the core–shell nanostructures is confirmed by detailed electron microscopy study, which gives more insight into the nanorod formation mechanism on 2D material. Mechanical transfer of nanostructures on sapphire substrates to copper tape is then demonstrated, with no resulting damage of nanorods. Use of MOVPE grown large‐area h‐BN to realize nanostructures is a significant advancement and can lead to new nanodevice architectures needed for next‐generation optoelectronic devices. [ABSTRACT FROM AUTHOR]