Epitaxy of high-quality single-crystal hexagonal perovskite YAlO3 on

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Epitaxy of high-quality single-crystal hexagonal perovskite YAlO on GaAs(111)A using laminated atomic layer deposition 3

Lawrence Boyu Young, Chao-Kai Cheng, Keng-Yung Lin, Yen-Hsun Lin, Hsien-Wen Wan, Ren-Fong Cai, Shen-Chuan Lo, Mei-Yi Li, Chia-Hung Hsu, Jueinai Kwo, and Minghwei Hong Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b01375 • Publication Date (Web): 14 Mar 2019 Downloaded from http://pubs.acs.org on March 14, 2019

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Crystal Growth & Design

Epitaxy of high-quality single-crystal hexagonal perovskite YAlO3 on GaAs(111)A using laminated atomic layer deposition Lawrence Boyu Young1,‡, Chao-Kai Cheng1,‡, Keng-Yung Lin1,‡, Yen-Hsun Lin1, Hsien-Wen Wan1, Ren-Fong Cai2, Shen-Chuan Lo2, Mei-Yi Li3, Chia-Hung Hsu4,*, Jueinai Kwo5,*, and Minghwei Hong1,* 1

Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei 10617, Taiwan Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu 31040, Taiwan 3 Taiwan Semiconductor Research Institute, Hsinchu 30078, Taiwan 4 National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan 5 Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan KEYWORDS: atomic layer deposition, laminated multilayers, hexagonal perovskite YAlO3, gallium arsenide, substrate induced epitaxy, oxide/semiconductor hetero-structure 2

ABSTRACT: Single-crystal metastable hexagonal perovskite YAlO3 (H-YAP) films were epitaxially grown on GaAs(111)A by utilizing sub-nano-laminated (snl) and nano-laminated (nl) atomic layer deposited (ALD) Y2O3/Al2O3 multilayers in-situ on freshly prepared pristine molecular beam epitaxy (MBE) GaAs. We have studied and compared the structures of H-YAP between the snlALD and nl-ALD samples using synchrotron radiation X-ray diffraction (SR-XRD) and scanning transmission electron microscopy (STEM). The evolution of SR-XRD data under different annealing conditions suggested a lowest temperature of 900oC for forming H-YAP. The observation of pronounced Pendellösung fringes indicated an excellent crystallinity of H-YAP and sharp H-YAP/GaAs interface despite an ~8.4% large lattice mismatch between H-YAP and GaAs. Narrow full width at half maximum (FWHM) ~0.019° of H-YAP(0004) θ-rocking scan of the snl-ALD sample is close to that of substrate GaAs(111) ~0.013o and one order of magnitude smaller than that of H-YAP(0004) of the nl-ALD sample ~0.280°, indicating a better crystallinity of the former than that of the latter. STEM images revealed the formation of H-YAP starting from the GaAs surface instead of inside the multilayers. The oxide/GaAs interface remained very sharp after 900oC annealing.

1. INTRODUCTION Multi-element compounds with structures related to perovskite exhibit various scientifically interesting and industrially important properties, including high dielectric constants1, superconductivity2, broadband optical emission3, photovoltaics4, ferroics5, and spintronics6. Integrating single-crystal perovskite thin films onto industrial-scaled semiconductor substrates such as Si and GaAs combines rich properties of the perovskites with advanced electronic and opto-electronic devices, enabling new technological functions. Atomic layer deposition (ALD), a thin film deposition method with advantages of sequential self-limiting surface reactions and conformal coverages, is being used by industries in fabricating commercial products; a notable example is the ALD-HfO2-based high-k gate dielectric in the complementary metal-oxide-semiconductor (CMOS) since the 45 nm node7. The as-deposited ALD-HfO2 and -Al2O38-12 are amorphous13,14. Growing single-crystal binary or ternary oxides epitaxially on semiconductors have been firstly succeeded using molecular beam epitaxy (MBE)15-18, and later using ALD19-24. Binary single-crystal Y2O3(111) and (110) were epitaxially grown on GaAs(111)A and (001), respectively, despite a large lattice mismatch between Y2O3 and GaAs25. The Y2O3/GaAs MOS capacitors have shown excellent electrical properties21,26. Extending the hetero-epitaxial growth from binary to ternary compounds using ALD is challenging.

We have previously attained a ternary single-crystal hexagonal perovskite YAlO3(0001) (H-YAP) epitaxially on GaAs(111)A by post-deposition rapid thermal annealing (RTA) ALD nanolaminated (nl) Y2O3(2.03 nm)/Al2O3(1.08 nm) multilayers to 900°C27. Furthermore, we have improved the crystallinity of HYAP by RTA ALD sub-nano-laminated (snl) Y2O3(0.51 nm)/Al2O3(0.27 nm) multilayers on GaAs(111)A. The excellent crystallinity was evidenced by the pronounced Pendellösung fringes of the XRD radial scans along surface normal and the narrow FWHM of H-YAP(0004) θ-rocking scan ~ 0.026°, which approaches ~ 0.013° of the GaAs substrate peak. A highquality epitaxy was obtained despite an ~8.4% large lattice mismatch between the substrate (GaAs) and the film (H-YAP). In this work, we have investigated the detailed crystallography, the epitaxial relationship, and the epitaxial growth of H-YAP on GaAs using both high-resolution synchrotron radiation Xray diffraction (SR-XRD) and atomic-scaled scanning transmission electron microscopy (STEM). The two differently stacked snl- and nl-ALD Y2O3/Al2O3 multilayers were prepared and compared. We have used RTA to anneal the samples in between 850°C and 900°C with various durations, which illustrated the different stages of the phase formation of H-YAP on GaAs(111)A.

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Figure 1. XRD surface normal scans of (a) snl-ALD, and (b) nl-ALD samples with various thermal treatments: (1) as-deposited, and RTA at (2) 850°C for 30 s, (3) 900°C for 2 s for snl-ALD, 10 s for nl-ALD, (4) 900°C for 30 s, (5) 900°C for 60 s, and (6) 900°C for 90 s. (c) θ-rocking scans of H-YAP(0004) of the sample after 900°C anneal for 60 s; the red and black curves represent the data of snl-ALD and nl-ALD samples, respectively. 2. EXPERIMENT The samples were prepared in a multi-chamber ultra-high vacuum (UHV) system, which includes thin-film growth chambers of MBE, ALD, and analysis chambers. All the chambers were connected using modules under UHV of ~10-10 torr28,29. The detailed sample growth was given previously27,30. The nominal thicknesses of Y2O3 and Al2O3 in the snl-ALD sample were 0.51 nm (3 cycles) and 0.27 nm (3 cycles) and the Y2O3/Al2O3 bilayer repeated 24 times. For the nl-ALD sample, 10 cycles of Y2O3 were first deposited as an initial layer, followed by 1.08nm Al2O3 (12 cycles)/2.03-nm Y2O3 (12 cycles) bilayer repeated twice, and finally 4-nm Al2O3 was deposited. We took the samples out of the UHV system, and rapid thermal annealed the samples to 850°C for 30 s and 900°C for 2 s (snl)/10 s (nl), 30 s, 60 s, and 90 s in He ambient to form the epitaxial layer with a desired phase. We have studied the crystallography of the H-YAP films/GaAs hetero-structures using SR-XRD in two different beamlines, BL17B and BL07A with 8 keV incident Xray energy at the Taiwan Light Source of the National Synchrotron Radiation Research Center (NSRRC). We employed a spherical aberration (Cs) corrected STEM (JEOL, JEMARM200F), operated at an accelerating voltage of 200 kV, at the Industrial Technology Research Institute (ITRI) to study the local structure at the interfacial region of the samples. The STEM samples were prepared by using focused ion beam (FIB) at the Taiwan Semiconductor Research Institute, Taiwan. 3. RESULTS AND DISCUSSION To understand the initial stage of the H-YAP formation on GaAs(111)A substrates from the laminated ALD-Y2O3/Al2O3 multilayers and the influences of annealing conditions on the HYAP structure, we systematically annealed the samples under various temperatures and durations. Our previous results revealed that the H-YAP was formed after 900°C annealing27,30. Here, we present the structural evolution of the snl-ALD and the nl-ALD samples annealed at 850°C for 30 s and 900°C for

various durations. Figure 1(a) shows the XRD radial scans along surface normal of the snl-ALD Y2O3/Al2O3 multilayers undergone different annealing conditions. Scattered X-ray intensity is plotted as a function of scattering vector q, whose magnitude is 4π × sin(2θ/2)/λ with 2θ and λ denoting the scattering angle and X-ray wavelength, respectively. Curve (1) was taken from the as-deposited sample. Two sharp intense substrate peaks, GaAs(111) and (222), were observed but no Bragg peaks associated with Y2O3, Al2O3 or H-YAP were identified. The XRD radial scan of the 850°C/30 s annealed sample, curve (2), is similar to that of the as-deposited sample except the oscillation fringes at low q (below 1 Å -1) region, which are the visible sign of the presence of the deposited layer. From the period of the fringes, we estimated the layer thickness to be approximately 11.4 nm. These fringes are also observed in all the annealed snl-ALD samples. Upon RTA at 900°C for 2 s, four pronounced diffraction peaks emerged, as illustrated in curve (3), an evidence of the development of a crystalline structure. The peak locations agree well with the expected positions of the H-YAP(0002), (0004), (0006) and (0008) reflections, from which a lattice constant of 1.057 nm was yielded. This value is close to the reported lattice constant c of bulk H-YAP, 1.052 nm31,32. From the reflections, we inferred that the c-axis of HYAP is aligned with the surface normal of the GaAs(111) substrate. Off-normal ϕ-cone scans across the non-specular HYAP{101̅2} reflections (not shown) further verified the hexagonal symmetry of the H-YAP films and the in-plane epitaxial relationship between H-YAP and GaAs. The lateral lattice parameter of the H-YAP determined by fitting the positions of {101̅2} reflections is 0.366 nm. The azimuthal angle (ϕ) of one of the six evenly spaced {101̅2} reflections coincides with that of GaAs(400) reflection27,30. From the relative positions of the non-specular diffraction peaks, the structure of the films is confirmed to be H-YAP with an epitaxial relationship of HYAP(0001)||GaAs(111)[101̅] 27,30.


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Figure 2. STEM images of (a) as-grown snl-ALD, (b) snl-ALD sample after 900°C 2 s, (c) 900°C 30 s annealing, (d) as-grown nlALD, (e) nl-ALD sample after 900°C 10 s, and (f) 900°C 30 s annealing. The images were taken along GaAs[11̅0] zone axis, with the growth and the lateral direction being GaAs[111] and GaAs[112̅]. TABLE I. List of measured thicknesses of H-YAP films under different annealing conditions Crystalline Thickness (nm) Annealing

Coherence Length

Conditions

of H-YAP(0004)

STEM

snl

nl

snl

nl

850oC 30 s 900oC 2 s

6.3

6.3

900oC 10 s

1.9

900oC 30 s

7.7

4.4

7.9

5.6

900oC 60 s

8.0

4.9

8.3

5.7

900oC 90 s

7.2

4.7

8.1

5.0

For the samples annealed at 900°C, the four H-YAP peaks shifted slightly toward higher q side and became narrower as the annealing duration increased from 2 s to 60 s. H-YAP(0008) reflection shifted from q = 4.754 Å -1 to 4.771 Å -1, manifesting a decrease of lattice constant to 1.053 nm. Upon further annealing to 90 s, the lattice constant remained unchanged. Employing the Scherrer equation to analyze the H-YAP(0004) peak width, we deduced the crystalline coherent length along the growth direction of each H-YAP layer. This is also a measure of crystalline layer thickness, which increased from 6.3 nm of the 2 s RTA sample to 7.7 nm and 8.0 nm as the RTA duration increased to 30 s and 60 s, as listed in Table 1. The increase of the coherent length reveals the growth of the crystalline layer thickness with annealing duration up to 60 s. As the annealing time further increased to 90 s, the coherent length reduced slightly to 7.2 nm. In contrast, the total film thicknesses, deduced from the

oscillation fringes at low q region (below 1 Å -1) of the curves (2) to (6) in Figure 1(a), decreased slightly from 11.4 nm to 10.7 nm. The density of ALD grown Al2O3 and Y2O3 are usually much lower than the reported bulk density because of the incorporation of residual chemicals and the disorder and defects in atomic packing33-37. The observed decrease of the film thickness upon annealing is attributed to the densification of the ALD film36,38-40. The difference between the total film thickness and the crystalline coherent length is ascribed to the remaining amorphous layer. A major proportion of the crystalline layer formed in the initial 2 s of the 900°C annealing; the crystalline layer became thicker and its structure was improved up to about 60 s of annealing. With a longer duration, the structure exhibited mild deterioration as indicated by the broadening of the Bragg peaks. The Pendellӧsung fringes near the H-YAP reflections provide an additional measure of the structural perfection of the crystalline layer. The persistence of the fringes over a larger q range indicates sharper interfaces and better crystalline structures. The progressively pronounced fringes with increasing annealing duration up to 60 s then degraded for 90 s are consistent with the variation of structural quality deduced from the Bragg reflection width. A similar structural evolution in the snl-ALD samples was also observed in the nl-ALD samples, as revealed by the XRD results illustrated in Figure 1(b). However, their structures are less ordered than those of the snl-ALD samples undergone similar thermal treatments. Instead of distinct peaks, two faint bumps appeared at the locations of H-YAP(0002) and (0004) reflections upon 900°C/10 s of annealing; they developed into prominent peaks after annealing for 30 s. From the peak width of HYAP(0004), we estimated that the coherence length of the crystalline layer varied between 4 nm and 5 nm for the nl-ALD samples annealed from 30 s to 90 s. No obvious oscillating fringes were found either at the low q range or near H-YAP reflections, an indication of rough interfaces. The θ-rocking curves across H-YAP(0004) reflection of the snl-ALD and nl-ALD samples after 900°C annealing for 60 s are depicted in red and black,


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respectively in Figure 1(c). The full width at half maximum (FWHM) of the snl-ALD sample is 0.019°, approaching to that of the (111) reflection of GaAs substrate, 0.013°. In comparison, the corresponding FWHM of the nl-ALD sample, 0.280°, is one order of magnitude broader than that of the snl-ALD sample ~0.019o. The smaller mosaicity, often an indication of a lower density of screw threading dislocations, elucidates the better crystallinity of the snl-ALD sample. We also performed STEM to examine the structural properties of the two series of samples to be complementary to the XRD results. Figure 2(a) shows the cross-sectional STEM Z-contrast image of the as-deposited snlALD sample. Interestingly, the first Y2O3 layer appeared in an epitaxial form but the Y2O3/Al2O3 multilayers above cannot be well resolved. Since Y atom is heavier than Al atom, Y2O3 should appear brighter than Al2O3 in a dark field image. However, no contrast difference appeared in the STEM image, indicating that the Y2O3 and Al2O3 layers are indiscernible and mixed. The total thickness of the snl-ALD layer deduced from the STEM image is about 11.87 nm, which is close to that derived from low q fringes of curve (2) in Figure 1(a). The measured thickness is about 2/3 of the nominal thickness, 18.72 nm, estimated from the growth per cycle (GPC) determined from similarly prepared thick ALD films. The nucleation behavior at the hetero-interface at the initial few ALD cycles often results in the reduction of the initial GPC, known as nucleation delay. This is commonly observed and accounts for the thinner measured film thicknesses as compared with the nominal ones41,42. Because only 3 ALD cycles were adopted in growing the snlALD sample, the impact of nucleation delay is expected to be significant, resulting in the large difference between the measured and nominal thickness of the as-deposited sample. After 900°C/2 s RTA, an about 6.32 nm thick well-ordered H-YAP crystalline layer formed, as shown in Figure 2(b). Note that the H-YAP/GaAs interface is atomically abrupt and flat, while the H-YAP/amorphous interface is ragged over several atomic layers. Annealing for 30 s led to an increase of the crystalline layer to 7.89 nm and the H-YAP/amorphous interface became smoother, as shown in Figure 2(c). The crystalline layer thicknesses derived from STEM images are tabulated in Table. 1 for comparison. The cross-sectional images of the nl-ALD samples undergoing a similar heat treatment are illustrated in Figure 2(d)-(f). For the as-deposited nl-ALD layer shown in Figure 2(d), alternating bright and dark slabs corresponding to Y2O3 and Al2O3 stacks form the 10.66 nm thick film. The measured thickness is about 95% of the nominal thickness, 11.22 nm; the reduced thickness difference in the nl-ALD sample as compared with that of the snl-ALD sample is attributed to the more ALD cycles for each constituent layer, as a consequence, the less influence of nucleation decay in the nl-ALD sample. Note that the ~1 nm thick bottom Y2O3 layer exhibited an ordered structure where the atomic packing is in registry with GaAs. The parallelogrammatic atomic packing tallies with the projection of Y atoms along Y2O3[11̅0] direction. The separation between the atomic planes along the growth direction, as marked by white lines in Figure 2(d), is approximately 0.31 nm, which agrees well with the spacing between consecutive Y atomic planes of cubic Y2O3 along the [111] direction, √3a_(c-Y2O3)/6 = 0.306 nm. From the image, we concluded that the Y2O3 layer had a cubic phase and grew on GaAs(111)A substrate obeying a B-type cube-on-cube growth, i.e., Y2O3[21̅1̅] ||GaAs[2̅11], agreeing with our results reported previously25. Because the bottom Y2O3 layer is only about one unit cell thick and not well ordered, as shown in Figure 2(d), which explains the lack of Y2O3 peaks in the curve (1) of Figure 1(b). Upon RTA to 900°C for 10 s, the atomic packing

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in the ~2 nm region immediately above the GaAs substrate transformed to a nearly ordered structure with a rectangular symmetry, as shown in Figure 2(e); the region above it remained amorphous. The atomic packing of the nearly ordered region agrees with the Y-sub-lattice projected onto the (112̅0) plane of H-YAP and gives rise to the faint bumps corresponding to the H-YAP(0002) and (0004) reflections in the XRD data depicted by curve (3) in Figure 1(b). Prolonged annealing for 30 s resulted in the growth of the H-YAP layer to 5.59 nm in consumption of the amorphous layer above. From the XRD and STEM results, the formation of epitaxial HYAP originated from the oxide/GaAs interface and progressively grew into the ALD multilayers; there was no evidence of nucleation inside the ALD layer. The sharp interface between the oxide/GaAs interface revealed no inter-diffusion of Al2O3 and Y2O3 into GaAs. The formation of H-YAP was much faster in the snl-ALD sample than in the nl-ALD sample. It took only 2 s to form a 6.32 nm thick H-YAP in the former and 10 s to form a 1.92 nm thick H-YAP in the latter after annealing at 900°C. The smaller thickness of the constituent oxide layers in the former case renders a rapid uniform intermixing of the two components because of the shorter diffusion distance. Viewing along the c-axis of H-YAP, the Y- (and Al-) sub-lattice on H-YAP basal plane has a hexagonal 2D lattice with a lattice constant a2D H-YAP(0001) = 0.366 nm, as shown in Figure 3. Similarly, projected along the [111] direction, both Ga- and As-sublattices in GaAs have a hexagonal 2D lattice with a lattice constant a2D GaAs(111) = 0.400 nm. The size ratio of the two sub-lattices is approximately 11:12. Inferring from the epitaxial relation determined by both XRD and STEM, 2D Y-sub-lattice of H-YAP(0001) plane is aligned with 2D Ga- and As-sub-lattice of GaAs(111) plane and has a lattice mismatch of ~8.4%. Hetero-epitaxy has been achieved by matching integral multiples of lattice planes across the interface as was reported previously in several material systems43-48.

Figure 3. Schematic of Y-sub-lattice of H-YAP and Ga-sublattice of GaAs as viewing along the c-axis of H-YAP and GaAs [111] direction. The shaded diamonds denote the 2D unit cell of Ga- and Y-sub-lattice.


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Crystal Growth & Design We enlarged the image of the H-YAP/GaAs interface region of Figure 2(c), as shown in Figure 4(a). Each chain of atoms connected by a solid and dashed line in Figure 3 is associated with a bright spot in GaAs and H-YAP in Figure 4(a), respectively. Well resolved H-YAP and GaAs crystalline planes manifest the excellent crystalline quality of the annealed snl-ALD sample. The magnified image of the region enclosed by the yellow rectangle is shown as an inset. The observed spacing between Y atoms along the growth and lateral direction are 1.07 nm and 0.31 nm, as marked by blue lines, consistent with the respective lattice constant cH-YAP = 1.052 nm and √3aH-YAP/2 = 0.317 nm; the latter is the projection of lattice constant aH-YAP onto HYAP[011̅0] direction. Also shown in the magnified image are the models of atomic packing of H-YAP projected along [ 21̅1̅0] and GaAs projected along [ 11̅0] . The positions of heavy Y atoms and GaAs dumbbells match the bright spots in STEM images nicely. The image again confirms the crystalline structure of H-YAP film and the H-YAP(0001) ∥ GaAs(111) [ 101̅] epitaxial relation, as determined from the XRD results. Figure 4(b) is the inverse fast Fourier transform (IFFT) filtered image of Figure 4(a). An additional HYAP(011̅0) plane appears every 11 GaAs planes. The associated misfit dislocations, as marked by , are regularly arranged at the oxide/GaAs interface. In the framework of domain matching epitaxy, a domain of 12 H-YAP planes matches a domain of 11 GaAs planes. Misfit dislocations accommodate the 8.4% large lattice mismatch and reduce an effective lattice mismatch down to less than 0.2%. The nearly full relaxation of H-YAP lattice achieved by introducing misfit dislocations right on the interface results in the observed excellent crystalline quality of the H-YAP film.

Figure 4. (a) STEM image of the snl-ALD sample after 900°C 30 s annealing and (b) its IFFT filtered image where misfit dislocations are marked. The inset in (a) is the magnification of the region enclosed by the yellow rectangle and the corresponding models of atomic packing. 4.

CONCLUSION We have grown ternary single crystal hexagonal perovskite YAlO3 films epitaxially on GaAs(111)A by RTA snl-ALD and nl-ALD Y2O3/Al2O3 multilayers to 900oC. Both XRD and STEM results verify the better crystalline quality of snl-ALD sample than nl-ALD one. STEM images revealed that the H-

YAP formation started from the oxide/GaAs interface instead of nucleation inside the ALD multilayers, indicating a substrate-induced epitaxy. The sharp interface between the HYAP/GaAs shown in the STEM images evidenced high thermodynamic stability between the H-YAP and GaAs to 900oC, similar to the Y2O3/GaAs interface. There was diffusion in the Y2O3/Al2O3 multilayers, but no inter-diffusion between the multilayers and GaAs. We have achieved an excellent heteroepitaxy of a ternary oxide on a binary semiconductor by subnano-laminated ALD despite a large lattice mismatch.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (Chia-hung Hsu) *E-mail: [email protected] (Jueinai R. Kwo) *E-mail: [email protected] (Minghwei Hong)

Author Contributions ‡ L.B.Y., C.K.C., and K.Y.L. contributed equally to this work. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was supported by the Ministry of Science and Technology, Taiwan (Grants MOST 105-2112-M-007-014-MY3, 1062112-M-002-010-, and 106-2622-8-002-001). We thank the technical support from Mr. Guan-Jie Lu.

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Epitaxy of high-quality single-crystal hexagonal perovskite YAlO3 on GaAs(111)A using laminated atomic layer deposition Lawrence Boyu Young1,‡, Chao-Kai Cheng1,‡, Keng-Yung Lin1,‡, Yen-Hsun Lin1, Hsien-Wen Wan1, Ren-Fong Cai2, Shen-Chuan Lo2, Mei-Yi Li3, Chia-Hung Hsu4,*, Jueinai Kwo5,*, and Minghwei Hong1,* 1

Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei 10617, Taiwan Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu 31040, Taiwan 3 Taiwan Semiconductor Research Institute, Hsinchu 30078, Taiwan 4 National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan 5 Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan KEYWORDS: atomic layer deposition, laminated multilayers, hexagonal perovskite YAlO3, gallium arsenide, substrate induced epitaxy, oxide/semiconductor hetero-structure 2

Single-crystal metastable phase hexagonal perovskite YAlO3 (H-YAP) films were epitaxially grown on GaAs(111)A by utilizing laminated ALD with post-deposition annealing. The experiment results suggested the HYAP was induced from the substrate instead of nucleation inside ALD multilayers. The excellent crystallinity of HYAP was obtained by introducing misfit dislocations right on the interface between H-YAP and GaAs.


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Epitaxy of high-quality single-crystal hexagonal perovskite YAlO3 on

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