TY - JOUR
T1 - Space-charge-controlled field emission analysis of current conduction in amorphous and crystallized atomic-layer-deposited Al2O3on GaN
AU - Hiraiwa, Atsushi
AU - Horikawa, Kiyotaka
AU - Kawarada, Hiroshi
N1 - Funding Information:
This research was supported by the “Program for Research and Development of Next-Generation Semiconductor to Realize Energy-Saving Society” (Program Grant Number JPJ005357) and the “Project of Creation of Life Innovation Materials for Interdisciplinary and International Researcher Development” of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. The sample preparation and electric measurements were carried out at the Research Organization for Nano and Life Innovation of Waseda University. The TEM images, SAED patterns, and XRD patterns were acquired at Kagami Memorial Research Institute for Materials Science and Technology of Waseda University with technical support from S. Enomoto (TEM and SAED) and T. Mino (XRD).
Publisher Copyright:
© 2021 Author(s).
PY - 2021/5/21
Y1 - 2021/5/21
N2 - As previously reported, postdeposition annealing at 800 °C and higher simultaneously crystallizes atomic-layer-deposited (ALD) Al2O3 films and reduces the current in Al/ALD-Al2O3/(0001) GaN capacitors by two orders of magnitude. This current reduction is caused by the enhancement of conduction band offset from 1.4 to 1.8 eV, as revealed by the space-charge-controlled field emission analysis. Selected area electron diffraction (SAED) patterns demonstrate that the crystallized films consist of twinned (111)-oriented cubic γ-Al2O3 with an epitaxial relation of Al2O3 ⟨ 0 1 ¯ 1 ⟩ ∥ GaN ⟨ 2 1 ¯ 1 ¯ 0 ⟩. The SAED patterns additionally include spots that are specific to triaxially tripled γ-Al2O3. The aforementioned epitaxy is due to the similarity of hexagonal close-packed sublattices between oxygen on a (111) γ-Al2O3 plane and nitrogen on a (0001) GaN plane. However, the hexagonal close-packed lattice constant of γ-Al2O3 is 12% smaller than that of GaN, necessitating domain matching epitaxy. The thickness of the interfacial transition layer caused by the large misfit is estimated to be thinner than four monolayers of oxygen sublattice, by using the methodology developed here. Based on these results, the effect of Al2O3 crystallinity on the characteristics of Al2O3/GaN capacitors, such as conduction current, dielectric breakdown, interface states, and bias instability, was comprehensively captured. According to x-ray diffraction analyses, Al2O3 films crystallize at 700 °C, which is ∼100 °C lower than the threshold temperature estimated by transmission electron microscope observations. This difference was possibly caused by locally crystallized Al2O3 films, as confirmed by the slightly reduced current. These findings form a basis for improving ALD-Al2O3 films as gate insulator.
AB - As previously reported, postdeposition annealing at 800 °C and higher simultaneously crystallizes atomic-layer-deposited (ALD) Al2O3 films and reduces the current in Al/ALD-Al2O3/(0001) GaN capacitors by two orders of magnitude. This current reduction is caused by the enhancement of conduction band offset from 1.4 to 1.8 eV, as revealed by the space-charge-controlled field emission analysis. Selected area electron diffraction (SAED) patterns demonstrate that the crystallized films consist of twinned (111)-oriented cubic γ-Al2O3 with an epitaxial relation of Al2O3 ⟨ 0 1 ¯ 1 ⟩ ∥ GaN ⟨ 2 1 ¯ 1 ¯ 0 ⟩. The SAED patterns additionally include spots that are specific to triaxially tripled γ-Al2O3. The aforementioned epitaxy is due to the similarity of hexagonal close-packed sublattices between oxygen on a (111) γ-Al2O3 plane and nitrogen on a (0001) GaN plane. However, the hexagonal close-packed lattice constant of γ-Al2O3 is 12% smaller than that of GaN, necessitating domain matching epitaxy. The thickness of the interfacial transition layer caused by the large misfit is estimated to be thinner than four monolayers of oxygen sublattice, by using the methodology developed here. Based on these results, the effect of Al2O3 crystallinity on the characteristics of Al2O3/GaN capacitors, such as conduction current, dielectric breakdown, interface states, and bias instability, was comprehensively captured. According to x-ray diffraction analyses, Al2O3 films crystallize at 700 °C, which is ∼100 °C lower than the threshold temperature estimated by transmission electron microscope observations. This difference was possibly caused by locally crystallized Al2O3 films, as confirmed by the slightly reduced current. These findings form a basis for improving ALD-Al2O3 films as gate insulator.
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U2 - 10.1063/5.0047200
DO - 10.1063/5.0047200
M3 - Article
AN - SCOPUS:85106655746
VL - 129
JO - Journal of Applied Physics
JF - Journal of Applied Physics
SN - 0021-8979
IS - 19
M1 - 195303
ER -