THE ASYMMETRIC BAND STRUCTURE AND ELECTRICAL BEHAVIOR OF THE GdScO3/GaN SYSTEM

III-V nitrides are interesting materials for a wide variety of electronic and optoelectronic devices. Their interaction with GdScO₃, a high-κ ternary rare earth oxide, is investigated for MOS applications. We compare pulsed laser deposited amorphous and crystalline epitaxial GdScO₃ in terms of their band alignment with the underlying GaN substrate and electrical characteristics of the MOS capacitors. The crystal structure of GdScO₃ and GaN is investigated by means of x-ray diffraction, certifying that crystalline oxide is growing epitaxially on GaN. X-ray photoelectron spectroscopy analysis shows a staggered band alignment with a GdScO₃-GaN valence band offset of 3.6-3.7 eV, which is reflected in a very asymmetric current-voltage behaviour of the MOS capacitors: breakdown at positive bias, significantly earlier for the crystalline oxide compared to the amorphous oxide, and no breakdown up to a field of -14 MV/cm at negative bias. Capacitance-voltage measurements were carried until reaching accumulation, despite the staggered band alignment, showing an oxide dielectric constant of 21.2. Transmission electron microscopy images show a crystalline, two-atom thick interface layer between GaN and both crystalline and amorphous GdScO₃, which is thought to be an electron barrier between GSO and GaN, a possible responsible for the accumulation and source of the staggered band alignment. The electrical behaviour can be exploited for asymmetric nano-electronic devices.

Reference:

¹ S. Iacopetti, P. Shekhter, R. Winter, T.C.U. Tromm, J. Schubert, and M. Eizenberg, 205303, 3 (2017).