Crystal Orientation of Cubic NiO Thin Films Formed on Monoclinic β‐Ga₂O₃ Substrates

Abstract

The crystal orientation relationship between cubic NiO and monoclinic β-Ga 2 O 3 in NiO thin films formed on ð201Þ, (010), and (001) β-Ga 2 O 3 substrates is investigated by X-ray diffraction analysis and cross-sectional transmission electron microscopy imaging. The NiO films formed on ð201Þ and (010) β-Ga 2 O 3 substrates satisfy the orientation relationships NiO (111) [011] ‖ β-Ga 2 O 3 ð201Þ [010] and NiO ð110Þ [110] ‖ β-Ga 2 O 3 (010) [001], respectively. In the NiO films on (001) β-Ga 2 O 3 substrates, the NiO plane near (133) is parallel to the (001) plane of β-Ga 2 O 3 under the relationship NiO [011] ‖ β-Ga 2 O 3 [010]. In addition, NiO films also satisfy the relationship NiO (100) ‖ β-Ga 2 O 3 (100) in each case. That is, for each case of ð201Þ, (010), and (001) β-Ga 2 O 3 substrates, the relationship of NiO (100) [011] ‖ β-Ga 2 O 3 (100) [001] is confirmed, consistent with the orientation relationship reported previously for NiO films on (100) β-Ga 2 O 3 substrates. The crystal orientation relationship is discussed in terms of the atomic arrangement models of NiO and β-Ga 2 O 3 .

Electrical Conductivity Studies in Sol–Gel‐Derived Li‐Doped NiO Epitaxial Thin Films

“…[ 13 ] In addition, we reported the epitaxial growth of NiO thin films on β‐Ga 2 O 3 substrates including the crystal orientation relationship between them. [ 15,16 ] Similar rectification characteristics of NiO/β‐Ga 2 O 3 pn heterojunction diodes were also reported by Schlupp et al [ 17 ]…”

“…[13] In addition, we reported the epitaxial growth of NiO thin films on β-Ga 2 O 3 substrates including the crystal orientation relationship between them. [15,16] Similar rectification characteristics of NiO/β-Ga 2 O 3 pn heterojunction diodes were also reported by Schlupp et al [17] Since the electrical properties of the NiO films play an important role in determining device performance, an understanding of the nature of carrier transport in NiO is needed. Highly stoichiometric NiO is a Mott insulator, but excess oxygen atoms in NiO result in the formation of nickel vacancies accompanied by the oxidation of Ni 2þ to Ni 3þ to preserve electrical neutrality.…”

Epitaxial relationship of NiO on ( 1̅ 02) β-Ga2O3

“…As a result, epitaxial NiO films on β-Ga 2 O 3 substrates maintain structural coherence within the ccp oxygen lattice, as evidenced by NiO films oriented along (100), ( 111), (110), and near (331) grown on commercially available (100), ( 201), (010), and (001) β-Ga 2 O 3 substrates, respectively. 14) Among the reported heterojunctions, only the (331) NiO/(001) β-Ga 2 O 3 configuration aligns with the higherindex (331) oxygen plane in the ccp lattice, causing the lowindex (110) of NiO to be tilted by 13.8°from the surface normal around the [010] axis of β-Ga 2 O 3 . 14) Therefore, the (001) β-Ga 2 O 3 substrate may not be the optimal choice when considering the heterojunction from the perspective of the ccp oxygen framework.…”

Operation of NiO/β-(Al0.21Ga0.79)2O3/Ga2O3 Heterojunction Lateral Rectifiers at up to 225 °C

“…The increased electrification of automobiles and the need to efficiently switch renewable energy into power grids or to charge electric vehicles has increased interest in the use of ultra-wide bandgap semiconductors like Ga 2 O 3 in power management and control systems. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] This could lead to faster switching at higher power levels for more efficient charging systems and improved control and protection of power distribution systems. [22][23][24][25][26][27][28][29][30] Thus, the target is the realization of more efficient, high-power, high-speed electronic converters containing rectifiers and switches.…”

“…[31][32][33][34][35][36] The absence of shallow acceptor dopants in this material 4,5 has prompted the use of p-type oxides to form p-n junctions with n-type Ga 2 O 3 . 6,7 The most successful of these has been NiO, usually deposited by sputtering in which the O 2 /Ar ratio can be used to control the conductivity. 8,9 The p-n junction has superior voltage blocking capability compared to Schottky rectifiers and ensures low leakage in the off state.…”