Unraveling the Heterointegration of 3D Semiconductors on Graphene by Anchor Point Nucleation

The heterointegration of graphene with semiconductor materials and the development of graphene-based hybrid functional devices are heavily bound to the control of surface energy. Although remote epitaxy offers one of the most appealing techniques for implementing 3D/2D heterostructures, it is only suitable for polar materials and is hugely dependent on the graphene interface quality. Here, the growth of defect-free single-crystalline germanium (Ge) layers on a graphene-coated Ge substrate is demonstrated by introducing a new approach named anchor point nucleation (APN). This powerful approach based on graphene surface engineering enables the growth of semiconductors on any type of substrate covered by graphene. Through plasma treatment, defects such as dangling bonds and nanoholes, which act as preferential nucleation sites, are introduced in the graphene layer. These experimental data unravel the nature of those defects, their role in nucleation, and the mechanisms governing this technique. Additionally, high-resolution transmission microscopy combined with geometrical phase analysis established that the as-grown layers are perfectly single-crystalline, stress-free, and oriented by the substrate underneath the engineered graphene layer. These findings provide new insights into graphene engineering by plasma and open up a universal pathway for the heterointegration of high-quality 3D semiconductors on graphene for disruptive hybrid devices.

Interface Modulation for the Heterointegration of Diamond on Si

Along with the increasing integration density and decreased feature size of current semiconductor technology, heterointegration of the Si-based devices with diamond has acted as a promising strategy to relieve the existing heat dissipation problem. As one of the heterointegration methods, the microwave plasma chemical vapor deposition (MPCVD) method is utilized to synthesize large-scale diamond films on a Si substrate, while distinct structures appear at the Si-diamond interface. Investigation of the formation mechanisms and modulation strategies of the interface is crucial to optimize the heat dissipation behaviors. By taking advantage of electron microscopy, the formation of the epitaxial β-SiC interlayer is found to be caused by the interaction between the anisotropically sputtered Si and the deposited amorphous carbon. Compared with the randomly oriented β-SiC interlayer, larger diamond grain sizes can be obtained on the epitaxial β-SiC interlayer under the same synthesis condition. Moreover, due to the competitive interfacial reactions, the epitaxial β-SiC interlayer thickness can be reduced by increasing the CH4 /H2 ratio (from 3% to 10%), while further increase in the ratio (to 20%) can lead to the broken of the epitaxial relationship. The above findings are expected to provide interfacial design strategies for multiple large-scale diamond applications.

Impact of 2D-3D Heterointerface on Remote Epitaxial Interaction through Graphene

Remote epitaxy has drawn attention as it offers epitaxy of functional materials that can be released from the substrates with atomic precision, thus enabling production and heterointegration of flexible, transferrable, and stackable freestanding single-crystalline membranes. In addition, the remote interaction of atoms and adatoms through two-dimensional (2D) materials in remote epitaxy allows investigation and utilization of electrical/chemical/physical coupling of bulk (3D) materials via 2D materials (3D-2D-3D coupling). Here, we unveil the respective roles and impacts of the substrate material, graphene, substrate-graphene interface, and epitaxial material for electrostatic coupling of these materials, which governs cohesive ordering and can lead to single-crystal epitaxy in the overlying film. We show that simply coating a graphene layer on wafers does not guarantee successful implementation of remote epitaxy, since atomically precise control of the graphene-coated interface is required, and provides key considerations for maximizing the remote electrostatic interaction between the substrate and adatoms. This was enabled by exploring various material systems and processing conditions, and we demonstrate that the rules of remote epitaxy vary significantly depending on the ionicity of material systems as well as the graphene-substrate interface and the epitaxy environment. The general rule of thumb discovered here enables expanding 3D material libraries that can be stacked in freestanding form.

Three-Dimensional Hetero-Integration of Faceted GaN on Si Pillars for Efficient Light Energy Conversion Devices

An important pathway for cost-effective light energy conversion devices, such as solar cells and light emitting diodes, is to integrate III-V (e.g., GaN) materials on Si substrates. Such integration first necessitates growth of high crystalline III-V materials on Si, which has been the focus of many studies. However, the integration also requires that the final III-V/Si structure has a high light energy conversion efficiency. To accomplish these twin goals, we use single-crystalline microsized Si pillars as a seed layer to first grow faceted Si structures, which are then used for the heteroepitaxial growth of faceted GaN films. These faceted GaN films on Si have high crystallinity, and their threading dislocation density is similar to that of GaN grown on sapphire. In addition, the final faceted GaN/Si structure has great light absorption and extraction characteristics, leading to improved performance for GaN-on-Si light energy conversion devices.