Van der Waals epitaxy of III-nitrides for liftoff and integration of thin films and devices
Dr. Michael Snure,
Air Force Research Laboratory, Sensors Directorate, WPAFB OH
Abstract: Heterogeneous integration of a diverse array of materials and devices on to a single platform is of growing interest to produce more compact and capable electronics systems. Integration at the chiplet level has proven successful; however, by isolating just the thin active layers and bonding them to a common substrate, even closer integration can be achieved further improving the size, weight, and power (SWAP). Isolation of the active material layer from the growth substrate can be achieved using a variety of methods: including substrate removal, laser liftoff, selective etching and mechanical liftoff. Van der Waals surfaces, such as graphene or hBN, offer a unique route to growth, transfer and integration of a wide variety of thin high quality electronic materials and devices. Specifically, sp2 bonded BN is interesting due to its atomically flat and smooth surface, high temperature and chemical stability, excellent insulating and dielectric properties, and ability to be grown uniformly over large areas (4”) by commercial techniques such as metal organic chemical vapor deposition. The properties of BN make it suitable for growth of variety of materials including III-nitrides, oxides, 2D materials, and other electronic films by a range of chemical and physical vapor deposition techniques. Here I will discuss the use of 2D boron nitride on sapphire templates for growth of high quality GaN and AlGaN/GaN high electron mobility transition (HEMT) structures. Some key growth challenges, including nucleation, template morphology and stability, and strain will be covered with the goal of achieving high quality films that can be easily lifted off and transferred. Mechanical liftoff techniques including both soft and spalling induced methods for transfer of full wafers, individual devices, and selectively defined areas will be discussed. With access to transferable GaN and AlGaN/GaN structures, I will discuss the effects of strain on basic materials properties like sheet carrier density and mobility, in the polarization induced AlGaN/GaN two-dimensional electron gas (2DEG). Transferred devices demonstrate exceptional transport properties with mobility > 2,000 cm2/Vs and device performance with GM of 300 mS/mm and fT and fmax > 34 GHz and 75 GHz under stain while bending. Lastly, I will cover bonding to high and low thermal conductivity substrates and the effects on device performance and self-heating. I hope to highlight the great potential of vdW epitaxy and liftoff for transfer and integration of high-performance thin films and devices on to various platforms.
Biography: Dr. Michael Snure is a senior research physicist in the Air Force Research Laboratory’s Electronic Devices Branch. His research focus is on growth and epitaxy of 2D materials, III-nitrides, III-Vs and II-VIs by a variety of chemical vapor deposition techniques including: MOCVD and HVPE. He has also worked extensively on combining 2D and 3D materials to form mixed dimensional (2D/3D) heterostructures for integration and fabrication of high-performance electronic devices.
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