Air Force

Method to grow and transfer gallium nitride crystals to flexible or non-flat surfaces

van der Waals assisted transfer approach used to demonstrate GaN LEDs on flexible substrates and AlGaN/GaN high electron mobility transistors (HEMT) on Cu substrates

Materials Electronics

Image shows approximately 40 GaN devices. The inset shows a close up of a flexible high electron mobility transistor.

Group III-nitride materials are of interest for producing electronic and optoelectronic integrated circuits that can be found in many electronic devices including solid-state lighting, radar, and 2D imaging arrays. For example, devices based on GaN, AlN, InN and their alloys are important for fabricating transistor circuits and light emitting devices. But one major limitation to producing these materials and devices is the lack of low cost, large area, and high-quality native substrates for their epitaxial growth. Sapphire has been the material of choice.

Now, Air Force researchers have developed a process for the growth of III-nitride materials, films, and device structures on 2D materials, such as graphene and boron nitride (BN). These substrates provide a significant cost advantage over sapphire. Further, the film can be lifted off from the substrate and transferred to a second substrate, which can be selected according to the application or desired features.

The process relies on weak out of plane van der Waals (vdW) bonding between 2D materials which relaxes the strict lattice matching requirements of typical 3D heterostructures. vdW materials are layered compounds, like graphite, hBN, molybdenite, etc., with strong chemical bonding in-plane and weak dispersive bonding between layers. The weak bonding between vdW layers enables the mechanical separation at the interface between two vdW layers, a vdW layer, and the substrate, or the vdW layer and the III-nitride material, or film.

The growth of III-nitride materials, films, and device structures on 2D materials, such as graphene and BN, is attractive for a number of applications including wearable systems, conformal radar, high-brightness light emitting diodes (LEDs) and high-power high-frequency electronic devices. The technology will further enable devices in a more compact and versatile form.

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