Phase control of α- and κ-Ga2O3 epitaxial growth on LiNbO3 and LiTaO3 substrates using α-Fe2O3 buffer layers

Abstract

LiNbO3 and LiTaO3 substrates are used in wide-bandwidth applications such as surface acoustic wave filter and show structural similarity to α-Ga2O3. In this study, we demonstrated the phase control of Ga2O3 epitaxial thin films, grown by mist chemical vapor deposition, on the (0001) planes of LiNbO3 and LiTaO3 substrates using α-Fe2O3 buffer layers. κ-Ga2O3 thin films were grown epitaxially on bare LiNbO3 and LiTaO3 substrates. Conversely, the insertion of the α-Fe2O3 buffer layer led to the preferential growth of the α-Ga2O3 epitaxial thin films. X-ray diffraction (XRD) φ-scan results revealed that the α-Ga2O3 thin films were grown along the same in-plane direction as that of the substrates. Besides, the XRD φ-scan results indicated that twin-free α-Ga2O3 was grown on the LiNbO3 and LiTaO3 substrates with the α-Fe2O3 buffer layers. The x-ray rocking curve scans of the asymmetric plane of α-Ga2O3 showed that the full width at half maximum values of α-Ga2O3 on the LiNbO3 and LiTaO3 substrates with the buffer layers were smaller than that of the c-plane α-Al2O3 substrate with and without the buffer layer. In addition, we grew the (11-20) and (1-100) planes of the α-Ga2O3 epitaxial thin films on the (11-20) and (1-100) planes of LiNbO3 substrates with the α-Fe2O3 buffer layer, respectively. This study showed that LiTaO3 and LiNbO3 are promising substrates for the epitaxial growth of α-Ga2O3 and κ-Ga2O3.

Single-Domain and Atomically Flat Surface of κ-Ga2O3 Thin Films on FZ-Grown ε-GaFeO3 Substrates via Step-Flow Growth Mode

“…However, research on κ-Ga 2 O 3 -based HEMT applications is still in its early stages and mainly concerned with thin film deposition and growth. The growth methods of κ-Ga 2 O 3 that have been reported to date include hydride vapor-phase epitaxy, , metal–organic chemical vapor deposition (MOCVD), − mist CVD, − molecular beam epitaxy (MBE), , and pulsed laser deposition (PLD). − Since κ-Ga 2 O 3 is a metastable phase, its phase-controlling techniques are essential for thin film growth. In MBE and PLD, which are categorized as physical vapor deposition methods, the phase control of κ-Ga 2 O 3 requires the assistance of Sn − or In .…”

“…It has been proposed that various substrates and templates can be used for the growth of κ-Ga 2 O 3 . These substrates include the following: (0001) α-Al 2 O 3, − ,,,− LiTaO 3, LiNbO 3 (rhombohedral), (0001) GaN, − AlN, ,, 6H-SiC (hexagonal), (111) yttria-stabilized zirconia (YSZ), , MgO, , STO, NiO, ITO (cubic), (201) β-Ga 2 O 3 , (monoclinic), and (100) SnO 2 (tetragonal). It has been found that κ-Ga 2 O 3 grew epitaxially on these substrates.…”

Observing the microstructure of a (001) κ-Ga2O3 thin film grown on a (−201) β-Ga2O3 substrate using automated crystal orientation mapping transmission electron microscopy

“…20 However, because it is difficult to grow the metastable κ phase as a single bulk crystal, it is important to select a suitable substrate for heteroepitaxial growth. Various substrates, such as (0001) α-Al 2 O 3 , [21][22][23][24][25][26] (0001) LiTaO 3 , 27 (0001) LiNbO 3 , 27 (0001) GaN, 21,25,28,29 (0001) AlN, 25,28,30,31 (0001) ZnO, 32 (111) YSZ, 33 (111) MgO, 33,34 (111) STO, 29,34 (111) NiO, 35 (100) SnO 2 , 18 and (−201) β-Ga 2 O 3 , 25,28 are used for the growth of κ-Ga 2 O 3 . It is noteworthy that the metastable κ-Ga 2 O 3 phase can be grown on β-Ga 2 O 3 substrates.…”

Sn-Induced Phase Stabilization and Enhanced Thermal Stability of κ-Ga2O3 Grown by Mist Chemical Vapor Deposition

“…Some of the early growth studies had reported the κ-phase (space group: P na 2 1 ) as the hexagonal ε-phase (space group: P6 3 mc). Recently, it was found that the ε-phase actually consists of 120°-rotated nanoscale κ-phase domains. , In an effort to improve the structural quality, the impacts of different substrates (sapphire, GaN, AlN, SrTiO 3 , yttria-stabilized ZrO 2 , and MgO) on the epitaxial growth have been investigated. − In addition to the crystal quality, the thermal stability of this metastable phase needs to be enhanced for the long-term reliability of a device operating under an extreme environment (i.e., high temperature and high pressure). Recently, several research groups reported that the introduction of elemental Sn during a Ga 2 O 3 growth could facilitate the preferential growth of the κ-phase. , So far, this phenomenon has been observed with physical vapor techniques such as pulsed laser deposition (PLD) and molecular beam epitaxy (MBE) but not with chemical vapor techniques to the best of our knowledge.…”