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## Creator

[Akihiro Ohtake](https://orcid.org/0000-0002-3519-4613), [Yusuke Hayashi](https://orcid.org/0000-0001-5672-1497)

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This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Akihiro Ohtake, Yusuke Hayashi; Controlled polarity inversion in GaAs/Ge/GaAs{111} heterostructures. Appl. Phys. Lett. 19 May 2025; 126 (20): 201601 and may be found at https://doi.org/10.1063/5.0271426.[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)

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[Controlled polarity inversion in GaAs/Ge/GaAs{111} heterostructures](https://mdr.nims.go.jp/datasets/19d65d0f-aae7-482b-85f0-59893c3a38b8)

## Fulltext

Controlled polarity inversion in GaAs/Ge/GaAs{111} heterostructuresAPL25-AR-02509Controlled polarity-inversion in GaAs/Ge/GaAs{111} heterostructuresAkihiro Ohtake1, a) and Yusuke Hayashi1National Institute for Materials Science (NIMS), Tsukuba 305-0044,Japan(Dated: 1 May 2025)We have fabricated the GaAs/Ge/GaAs heterostructures on the {111}-oriented substratesusing molecular-beam epitaxy for quasi-phase matching applications in nonlinear optics.The nonlinear optical coefficient of GaAs is beyond that of conventional LiNbO3, enablingmore efficient generation of entangled photon pairs via parametric down conversion. Weshow that GaAs films with either (111)A or (111)B orientation could be grown on theGe/GaAs{111} substrates, regardless of the polarity of the initial substrates; the (111)A-and (111)B-oriented GaAs overlayers were grown when the surfaces of Ge interlayerson the GaAs{111} substrates were terminated with 1 monolayer (ML)-Ga and 1 ML-In,respectively. Both (111)A- and (111)B-oriented GaAs overlayers have atomically flat sur-faces and are almost free of defects, such as rotational twins and stacking faults. Thepresent results provide a promising way to improve the efficiency of nonlinear optical pro-cesses in quasi-phase matching devices.a)Electronic mail: OHTAKE.Akihiro@nims.go.jp1This is the author’s peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset.PLEASE CITE THIS ARTICLE AS DOI: 10.1063/5.0271426III-V semiconductors, such as GaAs and AlAs, are promising materials for nonlinear opticaldevices, because their nonlinear susceptibilities are significantly higher than those of conventionalnonlinear optical crystals, e.g. β -BaB2O4, LiNbO3 and LiTaO3.1–6 Phase matching is essentialto realize nonlinear optical effects such as wavelength conversion, where the phase velocities ofthe excitation and conversion light must be identical. β -BaB2O4, which is most commonly usedfor deep ultraviolet generation, uses birefringence for phase matching by changing the angle ofincidence of the excitation light. LiNbO3 uses ferroelectricity to overcome weak birefringence forphase matching by periodically inverting the crystal polarity. This structure is called quasi-phasematching (QPM), because the phase velocity mismatch is compensated by periodically reversingthe sign of the nonlinear optical coefficient.7 Owing to the lack of remarkable birefringence andferroelectricity in III-V semiconductors, a variety of QPM structures have been developed to over-come the material-related constraints. Examples are periodical polarity inversion8,9 and verticalpolarity inversion10–13 using well-established technology for crystal growth and device fabrication.Molecular-beam epitaxy (MBE) has received increased attention for the fabrication of suchstructures, because of its superiority in controlling the thickness and composition of epitaxialfilms. This letter reports the fabrication of polarity-inverted structure of GaAs{111} using MBE.To achieve the polarity inversion, thin Ge films were used as interlayers. Since Ge (a=0.56754nm) and GaAs (a=0.56538 nm) have nearly the same lattice constant (mismatch=0.38 %) andtheir thermal expansion coefficients are quite close (5.73×10−6 K−1 for GaAs and 5.90×10−6K−1 for Ge), their interface is expected to be coherent and free of defect. Although the fabricationof GaAs/Ge/GaAs heterostructures on the {113}-14 and {111}-oriented15 GaAs substrates havebeen reported earlier, polarity-inverted structures are formed only on the (113)B and (111)A sub-strates, and the (113)B/Ge/(113)A and (111)A/Ge/(111)B structures have not been realized14,15.Here, we show that GaAs films with either (111)A- or (111)B-orientation could be grown on theGe/GaAs{111} substrates, regardless of the polarity of the initial GaAs substrates. The polarityof MBE-grown GaAs overlayers was identified on the basis of the surface characterization us-ing electron diffraction and scanning tunneling microscopy (STM). We found that the polarity ofGaAs overlayers is controlled by the surface treatments for the Ge interlayers on the GaAs{111}substrates: when the surface of the Ge/GaAs{111} substrate is terminated with 1 monolayer (ML)of Ga, the GaAs overlayers show a (2×2) surface reconstruction, characteristic of the (111)Asurface. On the other hand, the GaAs overlayers grown on the Ge interlayers terminated with 1ML of In show (√19×√19)-like surface reconstructions, providing the evidence for the (111)B-2This is the author’s peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset.PLEASE CITE THIS ARTICLE AS DOI: 10.1063/5.0271426oriented growth. In addition, we show that the formation of twin defects in both (111)A- and(111)B-oriented GaAs overlayers is effectively suppressed. The present growth technique makesit possible to successively grow alternating (111)A and (111)B layers of GaAs. This is expectedto increase the conversion efficiency of nonlinear optical processes.The growth experiments were carried out using a multi-chamber MBE system.16 The system isequipped with STM and X-ray photoelectron spectroscopy (XPS) apparatuses for online charac-terization. The clean surfaces of GaAs(111)A-(2×2) and (111)B-(√19×√19)-R23.4◦ were firstprepared by MBE.17 Thin Ge films were grown on the GaAs{111} substrates at 450◦C and weresubsequently annealed at 550◦C. The growth rate of Ge was approximately 0.015 bilayer (BL)/s,which was calibrated by using intensity oscillations of reflection high-energy electron diffrac-tion (RHEED) measurements on the (001)-oriented Ge substrate. Here, 1 BL of Ge is definedas 1.4×1015 atoms/cm2. The GaAs films were grown on the Ge films on GaAs substrates at450∼650◦C with an As4/Ga flux ratio ranging from 50 to 125. The growth rate was 0.02 BL/s (1BL of GaAs{111} consists of 1 ML of As and 1 ML of Ga.The growth processes were monitored by in situ RHEED with an electron-beam energy of 15keV. The samples were also characterized by online STM, XPS, and low-energy electron diffrac-tion (LEED). All the STM images were collected at room temperature (RT) in the constant currentmode with a tunneling current of 0.1 nA and sample voltages between −1.7∼−3.0 V. XPS mea-surements were performed using monochromatic Al Kα radiation (1486.6 eV). Photoelectronswere detected at an angle of 35◦ from the surface. The LEED patterns were recorded at RT usingprimary electron-beam energies ranging from 30 to 200 eV. We obtained LEED patterns at eightlocations across the sample, and confirmed the uniformity of the surface structures.The fabrication of GaAs/Ge/GaAs heterostructures consists of two main steps: the preparationof thin and uniform Ge interlayers on GaAs{111} substrates and the polarity-controlled growth ofGaAs overlayers on Ge interlayers. Fisrt, since no systematic studies have been reported for thepolarities of GaAs on Ge(111), we carried out the growth experiments of GaAs on bulk Ge(111)substrates to establish the growth procedures for the polarity-controlled GaAs overlayers. TheGe(111) surfaces were prepared by growing undoped buffer layers (50 BL-thick) on thermallycleaned Ge(111) substrates. In an attempt to control the polarity of the GaAs films, the Ge(111)surfaces were terminated with 1 ML of Ga (a) or As (b), prior to the growth of the GaAs overlayers.It has been reported that the As- and Ga-terminated Ge(111) surfaces have atomic structures inwhich the outermost Ge atoms of the ideal Ge(111) surface are replaced by As18 and Ga19 atoms,3This is the author’s peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset.PLEASE CITE THIS ARTICLE AS DOI: 10.1063/5.0271426FIG. 1. Typical filled-state STM images (A) of 10 BL-GaAs films grown on bulk Ge(111) substrates termi-nated with 1 ML of Ga (a), As (b), or In (c), and the corresponding RHEED (B) and LEED (C) patterns. TheSTM images were taken with a bias voltage of −3.0 V. Image dimensions are 500 nm × 450 nm. RHEEDpatterns were taken along the [101] direction of the Ge(111) substrate. LEED patterns were taken at 178eV (a) and 184 eV (b and c).respectively. It was therefore expected that the (111)B- and (111)A-oriented GaAs films wouldgrow on the As- and Ga-terminated Ge surfaces, respectively, similarly to the case for GaAs onAs/Si(111).20The GaAs film on the As-terminated Ge substrate was grown at 550◦C with an As4/Ga flux ratioof ∼70, whereas the film on the Ga-terminated Ge substrate was grown at 450◦C with an As4/Gaflux ratio of ∼120. As shown in Figs. 1(a)-B and 1(b)-B, the surfaces of the growing GaAsfilms on the Ga- and As-terminated Ge(111) substrates show (2×2) and (1×1) RHEED patterns,respectively, from the beginning of the growth (> 1 BL thickness). While only a Ga-rich (2×2)reconstruction is observed on the MBE-grown GaAs(111)A surface,21 under conventional MBEconditions, (√19×√19) and (1×1) structures are observed on the (111)B surface.21,22 Thus, it islikely that the GaAs films are grown with the (111)A and (111)B orientations on the Ga-terminatedand As-terminated Ge substrates, respectively, as expected.Figures 1(a) and 1(b) show typical filled-state STM images of 10 BL-GaAs films grown onthe Ga- and As-terminated Ge(111) substrates, respectively. The GaAs films grown on the As-terminated substrate consists of small islands; the majority of them have triangular and hexagonalshapes. The LEED pattern (inset in Fig. 1(b)) shows a sixfold symmetry, irrespective of theincident electron energy, indicating the formation of rotational twin domains. On the other hand,the GaAs films on the Ga-terminated substrate have a threefold symmetry (insets in Fig. 1(a))4This is the author’s peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset.PLEASE CITE THIS ARTICLE AS DOI: 10.1063/5.0271426and shows a rather flat surface morphology: the surface has a smaller root-mean-square roughness(Rq) value of 0.35 nm, as compared with that grown on the As-terminated substrate (1.27 nm).Previous studies have shown that the GaAs growth on Ge(111) usually is accompanied bythe formation of rotational twins.23,24 The existence of twin domains potentially induces opticalscattering and reduces carrier mobilities at the domain boundaries; it is therefore undesirable fordevice applications. As we will show below, the formation of twins in the (111)B-oriented filmwas greatly suppressed when the initial Ge surface was terminated with 1 ML-In. The growingsurface shows (1×1) RHEED patterns from the beginning of the growth, suggesting the onset ofthe (111)B-oriented growth. As shown in Fig. 1(c), the surface morphology is highly improved(Rq=0.140 nm), and the formation of rotational twins is effectively suppressed, as can be seenfrom the threefold LEED pattern.It is interesting to note that the In and Ga, both being group III elements, induce the GaAsgrowth with opposite polarities. Previous studies have shown that In- and Ga-terminated Ge(111)surfaces have similar atomic structures.19 On the other hand, it has been reported that the inter-diffusion occurs at the GaAs/Ge(111) interface.25 This suggests that the Ga- and In-terminatedGe(111) structures are not preserved at the GaAs/Ge interface, and that the complex atomic rear-rangement occurs at the interface.The next step in achieving the polarity-controlled GaAs/Ge/GaAs heterostructures is to obtainflat and uniform Ge thin layers on GaAs{111} substrates. The STM images and correspondingLEED patterns for 10 BL-Ge films grown on the GaAs(111)A-(2×2) and (111)B-(√19×√19)substrates are shown in Fig. S1 in the supplementary material. The Ge surfaces prepared on the(111)A and (111)B substrates have similar Rq values of 0.173 nm and 0.178 nm, respectively,whereas a slight difference was observed in step morphologies between the two surfaces. Thecorresponding LEED patterns clearly show a threefold symmetry, indicating that rotational twindomains are hardly formed in the Ge films.Having established the growth procedures for Ge interlayers and GaAs overlayers, we are nowin a position to fabricate polarity-controlled GaAs/Ge/GaAs{111} heterostructures. Figures 2(a)-2(d) show a series of RHEED patterns observed during the fabrication of the heterostructure onthe (111)A substrates. GaAs films were grown on the 10 BL-Ge layers on the GaAs substratesunder conditions otherwise identical to those for GaAs on bulk Ge. Prior to the growth of theGaAs overlayers, the surface of 10 BL-Ge(111) layers was terminated with 1 ML of Ga. Thegrowing GaAs films show (2×2) RHEED patterns (Fig. 2(c)), indicating the formation of a5This is the author’s peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset.PLEASE CITE THIS ARTICLE AS DOI: 10.1063/5.0271426FIG. 2. RHEED patterns taken during the growth of GaAs/Ge/GaAs heterostructures grown on the (111)A-oriented substrates: (a) the initial (111)A-(2×2) surface, (b) the 10 BL-Ge film, (c) as-grown 10 BL-GaAsfilm, and (d) 30 BL-GaAs film after annealing at 650◦C. The electron-incidence azimuth is [101]. TheRHEED pattern changes from (a) to (d) in an upward direction as the growth proceeds. (e) shows aschematic drawing of the heterostructure. (f) and (g) show STM images taken with a bias voltage of −3.0V from the as-grown 10 BL-thick GaAs film and the 30 BL-thick GaAs film after annealing at 650◦C, re-spectively. Image dimensions are 500 nm×500 nm. The inset in (g) shows the corresponding LEED patterntaken from the surface (178 eV).GaAs(111)A/Ge/GaAs(111)A heterostructure, as shown in Fig. 2(e). Figure 2(f) shows a filled-state STM image from the 10 BL-thick GaAs films grown at 450◦C; two-dimensional islands areobserved (Rq=0.28 nm). The density of the islands are significantly decreased after the annealingat 650◦C under the As flux, resulting in the improved surface morphology (Rq=0.16 nm) (see Fig.S2 in the supplementary material). The additional 20 BL-growth and the subsequent annealingat 650◦C further improved the surface morphology, as shown in Fig. 2(g) (Rq=0.14 nm). TheRHEED pattern shown in Fig. 2(d) is quite similar to that of the initial GaAs(111)A substrate(Fig. 2a), indicating that the overgrown GaAs film has the same orientation as the GaAs substrate.To promote the GaAs growth with the reversed orientation of (111)B, the surface of the Geinterlayers was terminated with 1 ML of In. Figures 3(a)-3(d) show RHEED patterns observedduring the growth on the Ge/GaAs(111)A substrate. The surface of the growing GaAs over-layer shows very weak (√19×√19) RHEED patterns, indicating the formation of polarity-invertedGaAs(111)B layers on the Ge/GaAs(111)A substrate (Fig. 3(e)). Although the optimum tempera-ture for the (111)B growth is 650◦C,17 the first 10 BL-GaAs film was grown at a lower temperature6This is the author’s peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset.PLEASE CITE THIS ARTICLE AS DOI: 10.1063/5.0271426FIG. 3. RHEED patterns taken during the growth of GaAs/Ge/GaAs heterostructures grown on the (111)A-oriented substrates: (a) the initial (111)A-(2×2) surface, (b) the 10 BL-Ge film, (c) as-grown 10 BL-GaAsfilm, and (d) 30 BL-GaAs film after annealing at 650◦C. The electron-incidence azimuth is [101]. TheRHEED pattern changes from (a) to (d) in an upward direction as the growth proceeds. (e) shows aschematic drawing of the heterostructure. (f) and (g) show STM images taken with a bias voltage of −3.0V from the as-grown 10 BL-thick GaAs film and the 30 BL-thick GaAs film after annealing at 650◦C, re-spectively. Image dimensions are 500 nm×500 nm. The inset in (g) shows the corresponding LEED patterntaken from the surface (169 eV).of 550◦C to suppress the possible desorption of In during the growth. The low-temperature growthresults in a slightly degraded surface morphology, as can be seen in Fig. 3(f) (Rq=0.273 nm), be-cause the surface diffusion of Ga atoms is less enhanced. Similarly to the case for the (111)Agrowth, the Rq value is decreased to 0.196 nm after the annealing at 650◦C, and the subsequent 20BL-growth at 650◦C further improves the surface morphology (Rq=0.158 nm), as shown in Fig.3(g).The polarity inversion of GaAs(111)B on Ge/GaAs(111)A was also confirmed by high-angleannular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy dis-persive x-ray spectroscopy (EDX). As shown in Fig. 4(a), both the GaAs/Ge and Ge/GaAs in-terfaces are coherent and the GaAs(111)B films are free of defects. The magnified STEM image(Fig. 4(b)) and atomically-resolved EDX image (Fig. 4(c)) clearly show that the GaAs films weregrown with the (111)B orientation on the Ge interlayers (see also Fig. S3 in the supplementarymaterial).We carried out the growth experiments on the GaAs(111)B substrate, and confirmed that7This is the author’s peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset.PLEASE CITE THIS ARTICLE AS DOI: 10.1063/5.0271426FIG. 4. (a) HAADF-STEM image of the polarity-inverted GaAs(111)B/Ge/GaAs(111)A heterostructure.The nominal thickness of GaAs films is 50 BL. Arrowheads indicate the positions of the GaAs/Ge andGe/GaAs interfaces. (b) Magnified STEM image. (c) Atomically-resolved EDX image of the region (b)with the Ga-K (blue) and As-K (red) lines. (d) EDX image of the Ge interlayers with the Ge-K line (green).Horizontal arrows indicate the positions of the interfaces.polarity-controlled heterostructures are also formed on the (111)B substrate (see Fig. S4 in thesupplementary material). On both substrates, the growth temperature (450◦C for (111)A, and550◦C and 650◦C for (111)B) is an important factor in determining the crystal quality of theovergrown GaAs film: (111)A-oriented GaAs films grown at 550◦C gives rise to a degradedsurface morphology with the formation of rotational twins. Similarly, the successive growth ofGaAs(111)B (> 10 BL) at 550◦C results in the degradation of the surface morphology and theformation of rotational twins.Figure 5(a) shows the STM image taken from the 30 BL-GaAs film grown on the Ga-terminatedGe layers on GaAs(111)A. A (2×2) periodicity is clearly seen, corresponding to the Ga-vacancybuckling structure (inset in Fig. 5(a)).26,27 Figure 5(c) shows LEED I−V curves for the 1 0 and 0 1beams measured from the 30 BL-GaAs films (red curves). Also shown are I−V curves measuredfrom the (2×2) surface on bulk GaAs(111)A (blue curves). An excellent agreement between the8This is the author’s peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset.PLEASE CITE THIS ARTICLE AS DOI: 10.1063/5.0271426FIG. 5. Typical STM images of the 30 BL-GaAs films grown on the Ga-terminated Ge layers (a) and 100BL-GaAs films grown on the In-terminated Ge layers (b) on the GaAs(111)A substrates. Image dimensionsare 8 nm×8 nm and 40 nm×40 nm, respectively. The images (a) and (b) were taken with bias voltages of−1.7 V and −3.0 V, respectively. The insets in (a) and (b) show the magnified images with dimensions of1.6 nm×2.1 nm and 6 nm×6 nm, respectively. (c) LEED I −V curves measured from the (111)A-(2×2)surfaces of 30 BL-GaAs (red curves) and bulk GaAs (blue curves). (d) LEED I −V curves measured fromthe (111)B-(√19×√19) surfaces of 50 BL-GaAs (red curves) and bulk GaAs (blue curves).two curves further confirms that the overgrown GaAs film has a (111)A orientation. The measuredI −V curves are well reproduced by the calculations for the Ga-vacancy buckling model (see Fig.S5 in the supplementary material).Shown in Fig. 5(b) is the magnified STM image observed from the thick GaAs film (100 BL)grown on the In-terminated Ge film (10 BL) on GaAs(111)A. There exist ordered and disorderedregions, and bright spots are arranged with a (√19×√19) periodicity in the ordered region (insetof Fig. 5(a)), indicating the formation of the (111)B surface. Further evidence for the (111)Borientation was obtained from the LEED measurements: as shown in Fig. 5(d), LEED I −V9This is the author’s peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset.PLEASE CITE THIS ARTICLE AS DOI: 10.1063/5.0271426curves measured from the 50 BL-thick GaAs films (red curves) and the (√19×√19) surface ofbulk GaAs(111)B (blue curves) are quite similar.Figures 6(a)-6(f) show magnified STM images of GaAs(111)B overlayers with various filmthicknesses grown on the Ge/GaAs(111)A substrate. The density of bright spots in STM images,corresponding to the hexagonal rings in the (√19×√19) structure,28 is below 50% at the earlystage of the growth, and is increased as the growth proceeds. This means that the (√19×√19)structure is incomplete on thinner GaAs(111)B films. As mentioned earlier, it has been re-ported that the interdiffusion occurs at the GaAs/Ge(111) interface.20 As shown in Fig. 6(h), ourXPS measurements show that the Ge 3d signal could be clearly seen in the spectrum measuredfrom the 20 BL-GaAs(111)B film (B), whereas the Ge intensity for the 20 BL-GaAs(111)A filmwas one order of magnitude smaller (A), suggesting that there was greater interdiffusion at theGaAs(111)B/Ge(111) interface. Therefore, it is plausible to consider that Ge atoms are incorpo-rated in thinner GaAs(111)B films growing at relatively high temperatures of 550◦C and 650◦C,which disturbs the formation of the (√19×√19) structure. As the film thickness increases, thenumber of Ge atoms in the GaAs film decreases because of the kinetic limitation of the diffusion,leading to pure GaAs(111)B growth with a (√19×√19) surface. The change in the surface struc-ture of the GaAs(111)B film is also observed in LEED I−V curves: the shape of the I−V curvesmeasured from the (111)B film strongly depends on the film thickness, whereas no noticeablechange was observed for the (111)A film, as shown in Fig. S6 in the supplementary material.In conclusion, we studied the polarity of MBE-grown GaAs{111} films on Ge/GaAs{111} sub-strates using complementary experimental techniques of RHEED, LEED, and STM. The insertionof thin Ge interlayers enables us to control the polarity of GaAs overlayers in GaAs/Ge/GaAs{111}heterostructures: the (111)A-oriented GaAs films are grown when the surface of Ge layers is ter-minated with 1 ML of Ga, while the termination with 1 ML of In leads to the (111)B-orientedGaAs growth. The present results are expected to increase the efficiency of GaAs-based QPMnonlinear optical devices. This technique also opens attractive possibilities for the generation ofentangled photon pairs via parametric down conversion.See supplementary material for the STM results of Ge films (Fig. S1), additional RHEEDand STM results (Figs. S2 and S4), HAADF-STEM and EDX images (Fig. S3), LEED I-Vcurve analysis for the (111)A-(2×2) surface (Fig. S5 and Table S1), and LEED I-V curves forGaAs(111)A and (111)B films with various thicknesses (Fig. S6).10This is the author’s peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset.PLEASE CITE THIS ARTICLE AS DOI: 10.1063/5.0271426FIG. 6. STM images of the GaAs(111)B films with a bias voltage of −3.0 V (a-f). Image dimensions are20 nm×20 nm. The (√19×√19) unit cell is indicated in (f). (g) shows the densities of bright spots in STMimages plotted as a function of the GaAs film thickness. (h) XPS spectra of Ga 3d, Ge 3d and As 3d. Thespectrum A (B) was obtained from the 20 BL-GaAs(111)A (GaAs(111)B) film on the Ga- (In-) terminatedGe layers.ACKNOWLEDGMENTSHelpful discussions with Dr. T. Mano are gratefully acknowledged.AUTHOR DECLARATIONSConflict of InterestThe authors have no conflicts to disclose.11This is the author’s peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset.PLEASE CITE THIS ARTICLE AS DOI: 10.1063/5.0271426Author ContributionsAkihiro Ohtake: Conceptualization (lead); Data curation (lead); Formal analysis (lead); In-vestigation (lead); Methodology (lead); Writing – original draft (lead); Writing – review & editing(lead). Yusuke Hayashi: Conceptualization (equal); Writing – review & editing (supporting)DATA AVAILABILITYThe data that support the findings of this study are available from the corresponding authorupon reasonable request.REFERENCES1I. Shoji, H. Nakamura, K. Ohdaira, T. Kondo, R. Ito, T. Okamoto, K. Tatsuki, and S. Kubota,Absolute measurement of second-order nonlinear-optical coefficients of β -BaB2O4 for visibleto ultraviolet second-harmonic wavelengths J. Opt. Soc. Am. B 16, 620-624 (1999).2I. Shoji, T. Kondo, and R. Ito, Second-order nonlinear susceptibilities of various dielectric andsemiconductor materials, Opt. Quantum Electron. 34, 797-833 (2002).3S. Buckley, M. Radulaski, J. Petykiewicz, K. G. Lagoudakis, J.-H. Kang, M. Brongersma, K.Biermann, and J. Vuc̆ković, Second-Harmonic Generation in GaAs Photonic Crystal Cavities in(111)B and (001) Crystal Orientations, ACS Photonics 1, 516-523 (2014).4L. Chang, A. Boes, P. Pintus, J. D. Peters, M. Kennedy, X.-W. Guo, N. Volet, S.-P. Yu, S. B. Papp,and J. E. Bowers, Strong frequency conversion in heterogeneously integrated GaAs resonators,APL Photonics 4, 036103 (2019).5E.J. Stanton, J. Chiles, N. Nader, G. Moody, N. Volet, L. Chang, J.E. Bowers, S. Woo Nam, andR.P. Mirin, Efficient second harmonic generation in nanophotonic GaAs-on-insulator waveg-uides, Opt. Express 28, 9521-9532 (2020).6M. Placke, J. Schlegel, F. Mann, P. Della Casa, A. Thies, M. Weyers, G. Tränkle, andS. Ramelow, Telecom-band spontaneous parametric down-conversion in AlGaAs-on-insulatorwaveguides, Laser Photonics Rev. 18 2301293 (2024).7M.M. Fejer, G.A. Magel, D.H. Jundt, and R.L. Byer, Quasi-phase-matched second harmonicgeneration: tuning and tolerances, IEEE J. Quantum Electron. 28, 2631–2654 (1992).12This is the author’s peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset.PLEASE CITE THIS ARTICLE AS DOI: 10.1063/5.02714268D. Alden, T. Troha, R. Kirste, S. Mita, Q. Guo, A. Hoffmann, M. Zgonik, R. Collazo, and Z.Sitar, Quasi-phase-matched second harmonic generation of UV light using AlN waveguides,Appl. Phys. Lett. 114, 103504 (2019).9S. Wang, T. Matsushita, T. Matsumoto, S. Yoshida, and T. Kondo, Quasi-phase matched differ-ence frequency generation in corrugation-reduced GaAs/AlGaAs periodically-inverted waveg-uides, Jpn. J. Appl. Phys. 58, SBBE01 (2019).10Y. Hayashi, R. Katayama, T. Akiyama, T. Ito, and H. Miyake, Polarity inversion of aluminumnitride by direct wafer bonding, Appl. Phys. Express, 11, 031003 (2018).11Z. Zhang, Y. Hayashi, T. Tohei, A. Sakai, V. Protasenko, J. Singhal, H. Miyake, H. G. Xing, D.Jena, and Y. Cho, Molecular beam homoepitaxy of N-polar AlN: Enabling role of aluminum-assisted surface cleaning, Sci. Adv. 8, eabo6408 (2022).12N. Yokoyama, Y. Morioka, T. Murata, H. Honda, K. Serita, H. Murakami, M. Tonouchi, S.Tokita, S. Ichikawa, and Y. Fujiwara, Second harmonic generation in GaN transverse quasi-phase-matched waveguide pumped with femtosecond laser, Appl. Phys. Express 15, 112002(2022).13H. Honda, S. Umeda, K. Shojiki, H. Miyake, S. Ichikawa, J. Tatebayashi, Y. Fujiwara, K. Serita,H. Murakami, and M. Tonouchi, 229 nm far-ultraviolet second harmonic generation in a verticalpolarity inverted AlN bilayer channel waveguide, Appl. Phys. Express 16, 062006 (2023).14X. Lu, N. Kumagai, Y. Minami, and T. Kitada, Sublattice reversal in GaAs/Ge/GaAs heterostruc-tures grown on (113)B GaAs substrates, Appl. Phys. Express 11, 015501 (2018).15S. Koh, T. Kondo, M. Ebihara, T. Ishiwada, H. Sawada, H. Ichinose, I. Shoji, and R. Ito,GaAs/Ge/GaAs sublattice reversal epitaxy on GaAs(100) and (111) substrates for nonlinear op-tical devices, Jpn. J. Appl. Phys. 38, L508-L511 (1999).16A. Ohtake, Surface reconstructions on GaAs(001), Surf. Sci. Rep. 63, 295-327 (2008).17A. Ohtake, N. Ha, and T. Mano, Extremely high- and low- density of Ga droplets onGaAs{111}A, B: surface polarity dependence, Cryst. Growth Des. 15, 485-488 (2015).18R.D. Bringans, R.I.G. Uhrberg, R.Z. Bachrach, and J.E. Northrup, Arsenic-Terminated Ge(111):An Ideal 1×1 Surface, Phys. Rev. Lett. 55, 533-536 (1985).19J. Zengenhagen, P.F. Lyman, M. Böhringer, and M.J. Bedzyk, Discommensurate reconstructionsof (111)Si and Ge induced by surface alloying with Cu, Ga, and In, phys. stat. sol. 204, 587-616(1997).13This is the author’s peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset.PLEASE CITE THIS ARTICLE AS DOI: 10.1063/5.027142620J.R. Patel, P.E. Freeland, M.S. Hybertsen, D.C. Jacobson, and J.A. Golovchenko, Location ofAtoms in the First Monolayer of GaAs on Si, Phys. Rev. Lett. 59, 2180 (1987).21D.A. Woolf, D.I. Westwood, and R.H. Williams, Surface reconstructions of GaAs(111)A and(111)B: A static surface phase study by reflection high-energy- electron diffraction, Appl. Phys.Lett. 62, 1370-1372 (1993).22D.A. Woolf, Z. Sobiesierski, D.I. Westwood, and R.H. Williams, The molecular beam epitaxialgrowth of GaAs/GaAs(111)B: doping and growth temperature studies, J. Appl. Phys. 71, 4908-4915.23Y. Kajikawa, Y. Son, H. Hayase, H. Ichiba, R. Mori, K. Ushirogouchi, and M. Irie, Suppressionof twin generation in the growth of GaAs on Ge(111), J. Cryst. Growth 477, 40-44 (2017).24D. Pelati, G. Patriarche, O. Mauguin, L. Largeau, L. Tranvers, F. Brisset, G. Glas, and F. Oehler,GaAs(111) epilayers grown by MBE on Ge(111): Twin reduction and polarity, J. Cryst. Growth519, 84-90 (2019).25R.D. Bringans, M.A. Olmstead, R.I.G. Uhrberg, and R.Z. Bachrach, Interface formation of GaAswith Si(100), Si(111), and Ge(111): Core-level spectroscopy for monolayer coverages of GaAs,Ga, and As, Phys. Rev. B 36, 9569-9580 (1987).26S.Y Tong, G. Xu, and W.N. Mei, Vacancy-buckling model for the (2×2) GaAs(111) surface,Phys. Rev. Lett. 52, 1693-1696 (1984).27A. Ohtake, J. Nakamura, T. Komura, T. Hanada, T. Yao, H. Kuramochi, and M. Ozeki, Surfacestructure of GaAs{111}A,B-(2×2), Phys. Rev. B 64, 045318 (2001).28H. Koga, Structure of GaAs(111)under Ga-rich condition: A√19×√19 reconstruction model,Phys. Rev. B 82, 113301 (2010)14This is the author’s peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset.PLEASE CITE THIS ARTICLE AS DOI: 10.1063/5.0271426