What is it about?
ABSTRACT We demonstrate robust ferroelectricity in single-crystalline wurtzite phase N-polar ScAlN/GaN heterostructures grown on on-axis c-plane sapphire substrates by molecular beam epitaxy. The exactly aligned crystallographic orientation among the ScAlN, GaN, and sapphire substrate has been confirmed using x-ray diffraction measurements. The nearly lattice-matched N-polar Sc0.21Al0.79N/GaN heterostructure shows a highly uniform coercive field (∼4.6 MV/cm at 10 kHz) and remnant polarization (∼90 μC/cm2) across the whole wafer. The reliability of N-polar Sc0.21Al0.79N/GaN ferroelectricity has been systemically characterized using retention and endurance tests. Both the coercive field and remnant polarization exhibit negligible degradation over 105 switching cycles, which is among the best reported for ferroelectric III-nitrides. This work offers a viable path for fully epitaxial heterogeneous integration of ferroelectricity into N-polar III-nitride heterostructures, which, together with the recent demonstration of fully epitaxial ferroelectric metal-polar ScAlN, will find important applications in next-generation high-power and high-frequency electronics, memory electronics, acoustic resonators and filters, optoelectronics, and integrated quantum photonics.
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Why is it important?
Tuning the crystal symmetry is an important path to harnessing the limits of materials. Through growing ferroelectric nitride in the N-polar form, the landscape of ferroelectric nitride heterostructures is extended to enable a wealth of innovative device designs and applications.
Perspectives
It surprises us that ferroelectric nitrides can be grown on both N-polar and M-polar GaN substrates. With the device concepts and applications promised by the daily-mature GaN technology, we hope this polarization tunability, which combines epitaxial and electrical control, will present a pivotal step toward next-generation high-power and high-frequency electronics, acoustic filters and resonators, optoelectronics, and integrated quantum photonics.
Ding Wang
University of Michigan
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This page is a summary of: Ferroelectric N-polar ScAlN/GaN heterostructures grown by molecular beam epitaxy, Applied Physics Letters, July 2022, American Institute of Physics,
DOI: 10.1063/5.0097117.
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