The asymmetric band structure and electrical behavior of the GdScO3/GaN system

Abstract

III-V nitrides are interesting materials for a very wide variety of electronic and optoelectronic devices. In this study, their interaction with GdScO 3 (GSO), a ternary rare earth oxide, is investigated for MOS applications. We compare pulsed laser deposited amorphous and crystalline epitaxial GdScO 3 in terms of their band alignment with the underlying GaN substrate and the resulting electrical characteristics of the MOS stack. The crystal structure of GdScO 3 and GaN is investigated by means of x-ray diffraction, showing that crystalline oxide is growing epitaxially on GaN. X-ray photoelectron spectroscopy analysis shows a staggered band alignment with a GdScO 3-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 (around 5 MV/cm) compared to the amorphous oxide (around 8 MV/cm), and no breakdown up to a field of À14 MV/cm at negative bias. Transmission electron microscopy images show a crystalline, two-atom thick interface layer between GaN and both crystalline and amorphous GdScO 3 , which is thought to be an electron barrier between GSO and GaN and a possible source of the staggered band alignment. The electrical behaviour can be exploited for asymmetric nano-electronic devices. Published by AIP Publishing.

Epitaxial Oxides on Semiconductors: From Fundamentals to New Devices

“…Previous works have looked at a wide range of epitaxial oxides, of various crystal structures and compositions as high‐ k insulators on GaN, using MBE, PLD, and ALD, with some examples listed in Table . We note that MBE‐grown hexagonal Gd 2 O 3 and monoclinic PLD‐grown perovskite GdScO 3 as top performers, obtaining leakage currents on the order of μA cm −2 at 1.5 MV cm −1 , and permittivities of ≈24.…”

(Invited, Digital Presentation) High-κ Gate Oxide Integration and Ohmic Contact Development for AlGaN/GaN MISHEMTs

“…Epitaxially grown GdScO 3 as crystalline gate dielectric GdScO 3 can be epitaxially grown on GaN via pulsed laser deposition (PLD) at 700°C [21,22]. The high growth temperature and the already crystalline structure makes it thermally very stable and the integration with a high-κ first process possible.…”

“…The high growth temperature and the already crystalline structure makes it thermally very stable and the integration with a high-κ first process possible. Additionally, the high dielectric constant of κ 24-30 [22] is beneficial for achieving a small threshold voltage shift due to a low impact of the high capacitance in series. It was determined, that a 20 nm thick GdScO 3 is necessary for a good passivation with a low gate leakage current, even slightly below the Al 2 O 3 passivated MISHEMTs [23].…”

Controlled Two-Step Formation of Faceted Perovskite Rare-Earth Scandate Nanoparticles

“…LuScO 3 , for example, has only formed the perovskite phase when epitaxially stabilized on a NdGaO 3 or DyScO 3 substrate [40]. As these materials have mostly been used as dielectrics [41], substrates [36], and recently, flexoelectrics [42], they have often been prepared as thin films by atomic layer deposition [43] or pulsed laser deposition [44,45], or as single crystals using the Czochralski technique [36]. Using these materials in applications that require high surface area powders, such as heterogeneous catalysis [46] or gas capture [47] and separation [48], requires a different approach.…”