Showing papers on "Epitaxy published in 2018"

Diffusion-Controlled Epitaxy of Large Area Coalesced WSe2 Monolayers on Sapphire

Abstract: A multistep diffusion-mediated process was developed to control the nucleation density, size, and lateral growth rate of WSe2 domains on c-plane sapphire for the epitaxial growth of large area monolayer films by gas source chemical vapor deposition (CVD). The process consists of an initial nucleation step followed by an annealing period in H2Se to promote surface diffusion of tungsten-containing species to form oriented WSe2 islands with uniform size and controlled density. The growth conditions were then adjusted to suppress further nucleation and laterally grow the WSe2 islands to form a fully coalesced monolayer film in less than 1 h. Postgrowth structural characterization demonstrates that the WSe2 monolayers are single crystal and epitaxially oriented with respect to the sapphire and contain antiphase grain boundaries due to coalescence of 0° and 60° oriented WSe2 domains. The process also provides fundamental insights into the two-dimensional (2D) growth mechanism. For example, the evolution of doma...

Realizing Large-Scale, Electronic-Grade Two-Dimensional Semiconductors

Abstract: Atomically thin transition metal dichalcogenides (TMDs) are of interest for next-generation electronics and optoelectronics. Here, we demonstrate device-ready synthetic tungsten diselenide (WSe2) via metal–organic chemical vapor deposition and provide key insights into the phenomena that control the properties of large-area, epitaxial TMDs. When epitaxy is achieved, the sapphire surface reconstructs, leading to strong 2D/3D (i.e., TMD/substrate) interactions that impact carrier transport. Furthermore, we demonstrate that substrate step edges are a major source of carrier doping and scattering. Even with 2D/3D coupling, transistors utilizing transfer-free epitaxial WSe2/sapphire exhibit ambipolar behavior with excellent on/off ratios (∼107), high current density (1–10 μA·μm–1), and good field-effect transistor mobility (∼30 cm2·V–1·s–1) at room temperature. This work establishes that realization of electronic-grade epitaxial TMDs must consider the impact of the TMD precursors, substrate, and the 2D/3D inte...

AlGaN-based deep UV LEDs grown on sputtered and high temperature annealed AlN/sapphire

Abstract: The performance characteristics of AlGaN-based deep ultraviolet light emitting diodes (UV-LEDs) grown by metalorganic vapor phase epitaxy on sputtered and high temperature annealed AlN/sapphire templates are investigated and compared with LEDs grown on epitaxially laterally overgrown (ELO) AlN/sapphire. The structural and electro-optical properties of the devices on 350 nm sputtered and high temperature annealed AlN/sapphire show similar defect densities and output power levels as LEDs grown on low defect density ELO AlN/sapphire templates. After high temperature annealing of the 350 nm sputtered AlN, the full widths at half maximum of the (0002) and (101¯2) reflections of the high resolution x-ray diffraction rocking curves decrease by one order of magnitude to 65 arc sec and 240 arc sec, respectively. The curvature of the sputtered and HTA AlN/sapphire templates after regrowth with 400 nm MOVPE AlN is with −80 km−1 much lower than the curvature of the ELO AlN/sapphire template of −160 km−1. The on-wafer measured output powers of 268 nm LEDs grown on 350 nm sputtered and high temperature annealed AlN/sapphire templates and ELO AlN/sapphire templates were 0.70 mW and 0.72 mW at 20 mA, respectively (corresponding to an external quantum efficiency of 0.75% and 0.78%). These results show that sputtered and high temperature annealed AlN/sapphire provide a viable approach for the fabrication of efficient UVC-LEDs with reduced complexity and thus reduced costs.

Growth and characterization of α-, β-, and ϵ-phases of Ga2O3 using MOCVD and HVPE techniques

Abstract: Heteroepitaxial films of GaO were grown on c-plane sapphire (0001). The stable phase β-GaO was grown using the metalorganic chemical vapor deposition technique, regardless of precursor flow rates, ...

GaN/NbN epitaxial semiconductor/superconductor heterostructures.

Abstract: Epitaxy is a process by which a thin layer of one crystal is deposited in an ordered fashion onto a substrate crystal. The direct epitaxial growth of semiconductor heterostructures on top of crystalline superconductors has proved challenging. Here, however, we report the successful use of molecular beam epitaxy to grow and integrate niobium nitride (NbN)-based superconductors with the wide-bandgap family of semiconductors-silicon carbide, gallium nitride (GaN) and aluminium gallium nitride (AlGaN). We apply molecular beam epitaxy to grow an AlGaN/GaN quantum-well heterostructure directly on top of an ultrathin crystalline NbN superconductor. The resulting high-mobility, two-dimensional electron gas in the semiconductor exhibits quantum oscillations, and thus enables a semiconductor transistor-an electronic gain element-to be grown and fabricated directly on a crystalline superconductor. Using the epitaxial superconductor as the source load of the transistor, we observe in the transistor output characteristics a negative differential resistance-a feature often used in amplifiers and oscillators. Our demonstration of the direct epitaxial growth of high-quality semiconductor heterostructures and devices on crystalline nitride superconductors opens up the possibility of combining the macroscopic quantum effects of superconductors with the electronic, photonic and piezoelectric properties of the group III/nitride semiconductor family.

Surface-Guided CsPbBr3 Perovskite Nanowires on Flat and Faceted Sapphire with Size-Dependent Photoluminescence and Fast Photoconductive Response.

Abstract: All-inorganic lead halide perovskite nanowires have been the focus of increasing interest since they exhibit improved stability compared to their hybrid organic–inorganic counterparts, while retaining their interesting optical and optoelectronic properties. Arrays of surface-guided nanowires with controlled orientations and morphology are promising as building blocks for various applications and for systematic research. We report the horizontal and aligned growth of CsPbBr3 nanowires with a uniform crystallographic orientation on flat and faceted sapphire surfaces to form arrays with 6-fold and 2-fold symmetries, respectively, along specific directions of the sapphire substrate. We observed waveguiding behavior and diameter-dependent photoluminescence emission well beyond the quantum confinement regime. The arrays were easily integrated into multiple devices, displaying p-type behavior and photoconductivity. Photodetectors based on those nanowires exhibit the fastest rise and decay times for any CsPbBr3-b...

High-Brightness Blue Light-Emitting Diodes Enabled by a Directly Grown Graphene Buffer Layer.

Abstract: Single-crystalline GaN-based light-emitting diodes (LEDs) with high efficiency and long lifetime are the most promising solid-state lighting source compared with conventional incandescent and fluorescent lamps. However, the lattice and thermal mismatch between GaN and sapphire substrate always induces high stress and high density of dislocations and thus degrades the performance of LEDs. Here, the growth of high-quality GaN with low stress and a low density of dislocations on graphene (Gr) buffered sapphire substrate is reported for high-brightness blue LEDs. Gr films are directly grown on sapphire substrate to avoid the tedious transfer process and GaN is grown by metal-organic chemical vapor deposition (MOCVD). The introduced Gr buffer layer greatly releases biaxial stress and reduces the density of dislocations in GaN film and Inx Ga1-x N/GaN multiple quantum well structures. The as-fabricated LED devices therefore deliver much higher light output power compared to that on a bare sapphire substrate, which even outperforms the mature process derived counterpart. The GaN growth on Gr buffered sapphire only requires one-step growth, which largely shortens the MOCVD growth time. This facile strategy may pave a new way for applications of Gr films and bring several disruptive technologies for epitaxial growth of GaN film and its applications in high-brightness LEDs.

High-Performance Photodetectors Based on Solution-Processed Epitaxial Grown Hybrid Halide Perovskites

Abstract: Hybrid organic–inorganic halide perovskites (HOIPs) have recently attracted tremendous attention because of their excellent semiconducting and optoelectronic properties, which exist despite their morphology and crystallinity being far inferior to those of more mature semiconductors, such as silicon and III–V compound semiconductors. Heteroepitaxy can provide a route to achieving high-performance HOIP devices when high crystalline quality and smooth morphology are required, but work on heteroepitaxial HOIPs has not previously been reported. Here, we demonstrate epitaxial growth of methylammonium lead iodide (MAPbI3) on single crystal KCl substrates with smooth morphology and the highest carrier recombination lifetime (∼213 ns) yet reported for nonsingle crystalline MAPbI3. Experimental Raman spectra agree well with theoretical calculations, presenting in particular a sharp peak at 290 cm–1 for the torsional mode of the organic cations, a marker of orientational order and typically lacking in previous repor...

Growth Pressure Controlled Nucleation Epitaxy of Pure Phase ε- and β-Ga2O3 Films on Al2O3 via Metal–Organic Chemical Vapor Deposition

Abstract: Pure e- and β-phase gallium oxide (Ga2O3) films have been successfully grown on Al2O3 (001) substrate via metal–organic chemical vapor deposition (MOCVD) at a growth temperature of 500 °C. Growth pressure controlled nucleation is the dominant controlling parameter for pure phase Ga2O3 film growth. Due to the biaxial stress induced by lattice mismatch, heteroepitaxial e-phase Ga2O3 is grown on Al2O3 by heterogeneous nucleation at low pressure. However, film growth is dominated by spherical nuclei homogeneous nucleation at a pressure higher than 100 mbar, and β-phase Ga2O3 film is grown with a mosaic surface. The optimum pressure for the growth of pure e-Ga2O3 films with superior crystallinity is 35 mbar, whereas the pressure window for pure β-Ga2O3 growth is between 100 mbar and 400 mbar. The growth rate of β-Ga2O3 film is much lower than e-Ga2O3 film at high pressure. On the other hand, all Ga2O3 films have shown good optical properties with a band gap of about 4.9 eV. This fundamental research will help ...

Molecular beam epitaxy of quasi-freestanding transition metal disulphide monolayers on van der Waals substrates: a growth study

Abstract: Based on an ultra-high vacuum compatible two-step molecular beam epitaxy synthesis with elemental sulphur, we grow clean, well-oriented, and almost defect-free monolayer islands and layers of the transition metal disulphides MoS2, TaS2 and WS2. Using scanning tunneling microscopy and low energy electron diffraction we investigate systematically how to optimise the growth process, and provide insight into the growth and annealing mechanisms. A large band gap of 2.55 eV and the ability to move flakes with the scanning tunneling microscope tip both document the weak interaction of MoS2 with its substrate consisting of graphene grown on Ir(1 1 1). As the method works for the synthesis of a variety of transition metal disulphides on different substrates, we speculate that it could be of great use for providing hitherto unattainable high quality monolayers of transition metal disulphides for fundamental spectroscopic investigations.

Surface-Mediated Aligned Growth of Monolayer MoS2 and In-Plane Heterostructures with Graphene on Sapphire

Abstract: Aligned growth of transition metal dichalcogenides and related two-dimensional (2D) materials is essential for the synthesis of high-quality 2D films due to effective stitching of merging grains. H...

Considerations for Utilizing Sodium Chloride in Epitaxial Molybdenum Disulfide

Abstract: The utilization of alkali salts, such as NaCl and KI, has enabled the successful growth of large single domain and fully coalesced polycrystalline two-dimensional (2D) transition-metal dichalcogenide layers However, the impact of alkali salts on photonic and electronic properties is not fully established In this work, we report alkali-free epitaxy of MoS2 on sapphire and benchmark the properties against alkali-assisted growth of MoS2 This study demonstrates that although NaCl can dramatically increase the domain size of monolayer MoS2 by 20 times, it can also induce strong optical and electronic heterogeneities in as-grown, large-scale films This work elucidates that utilization of NaCl can lead to variation in growth rates, loss of epitaxy, and high density of nanoscale MoS2 particles (4 ± 07/μm2) Such phenomena suggest that alkali atoms play an important role in Mo and S adatom mobility and strongly influence the 2D/sapphire interface during growth Compared to alkali-free synthesis under the same growth conditions, MoS2 growth assisted by NaCl results in >1% tensile strain in as-grown domains, which reduces photoluminescence by ∼20× and degrades transistor performance

Flow modulation epitaxy of hexagonal boron nitride

Abstract: Growth of hexagonal boron nitride (hBN) layers on 2'' sapphire substrate using metal organic vapour phase epitaxy is reported here, where we compare the growth under continuous flow and flow modulation (FM) schemes. hBN films grown under the continuous flow regime exhibit low growth rate and rough surface profiles due to severe parasitic reactions between precursor molecules, which are suppressed by adopting a FM scheme. We also observe spontaneous delamination of hBN films from the substrate when immersed in a water bath and attribute this to be due to relaxation of compressive stress in the films, which was further corroborated using Raman spectroscopy. Carbon is identified as a major impurity which gets incorporated as boron carbide under FM growth and results in large sub-bandgap fluorescence in the range of 1.77–2.25 eV. Overall, hBN films deposited using the FM scheme at low growth rate (~2–3 nm h−1) exhibited the best characteristics in the present study, which will be suitable for applications such as van der Waals epitaxy and 2D hetero-structure devices.

Methods for forming silicon-containing epitaxial layers and related semiconductor device structures

Abstract: A method for forming a silicon-containing epitaxial layer is disclosed. The method may include, heating a substrate to a temperature of less than approximately 950° C. and exposing the substrate to a first silicon source comprising a hydrogenated silicon source, a second silicon source, a dopant source, and a halogen source. The method may also include depositing a silicon-containing epitaxial layer wherein the dopant concentration within the silicon-containing epitaxial layer is greater than 3×10 21 atoms per cubic centimeter.

Realization of vertical metal semiconductor heterostructures via solution phase epitaxy.

Abstract: The creation of crystal phase heterostructures of transition metal chalcogenides, e.g., the 1T/2H heterostructures, has led to the formation of metal/semiconductor junctions with low potential barriers. Very differently, post-transition metal chalcogenides are semiconductors regardless of their phases. Herein, we report, based on experimental and simulation results, that alloying between 1T-SnS2 and 1T-WS2 induces a charge redistribution in Sn and W to realize metallic Sn0.5W0.5S2 nanosheets. These nanosheets are epitaxially deposited on surfaces of semiconducting SnS2 nanoplates to form vertical heterostructures. The ohmic-like contact formed at the Sn0.5W0.5S2/SnS2 heterointerface affords rapid transport of charge carriers, and allows for the fabrication of fast photodetectors. Such facile charge transfer, combined with a high surface affinity for acetone molecules, further enables their use as highly selective 100 ppb level acetone sensors. Our work suggests that combining compositional and structural control in solution-phase epitaxy holds promises for solution-processible thin-film optoelectronics and sensors.

Investigation of GaN-on-GaN vertical p-n diode with regrown p-GaN by metalorganic chemical vapor deposition

Abstract: To mimic selective-area doping, p-GaN was regrown on an etched GaN surface on GaN substrates by metalorganic chemical vapor deposition. Vertical GaN-on-GaN p-n diodes were fabricated to investigate the effects of the etch-then-regrowth process on device performance. The crystal quality of the sample after each epitaxial step was characterized by X-ray diffraction, where the etch-then-regrowth process led to a very slight increase in edge dislocations. A regrowth interfacial layer was clearly shown by transmission electron microscopy. Strong electroluminescence was observed with three emission peaks at 2.2 eV, 2.8 eV, and 3.0 eV. The forward current density increased slightly with increasing temperature, while the reverse current density was almost temperature independent indicating tunneling as the reverse transport mechanism. This result is very similar to the reported Zener tunnel diode comprising a high doping profile at the junction interface. High levels of silicon and oxygen concentrations were observed at the regrowth interface with a distribution width of ∼100 nm. This work provides valuable information on p-GaN regrowth and regrown GaN p-n diodes, which can serve as an important reference for developing selective doping for advanced GaN power electronics for high voltage and high power applications.

Hydrogen-Assisted Epitaxial Growth of Monolayer Tungsten Disulfide and Seamless Grain Stitching

Abstract: Recently, research on transition metal dichalcogenides (TMDCs) has been accelerated by the development of large-scale synthesis based on chemical vapor deposition (CVD). However, in most cases, CVD-grown TMDC sheets are composed of randomly oriented grains, and thus contain many distorted grain boundaries (GBs) which deteriorate the physical properties of the TMDC. Here, we demonstrate the epitaxial growth of monolayer tungsten disulfide (WS2) on sapphire by introducing a high concentration of hydrogen during the CVD process. As opposed to the randomly oriented grains obtained in conventional growth, the presence of H2 resulted in the formation of triangular WS2 grains with the well-defined orientation determined by the underlying sapphire substrate. Photoluminescence of the aligned WS2 grains was significantly suppressed compared to that of the randomly oriented grains, indicating a hydrogen-induced strong coupling between WS2 and the sapphire surface that has been confirmed by density functional theory ...

Self-Assembled UV Photodetector Made by Direct Epitaxial GaN Growth on Graphene.

Abstract: Hybrid systems based on the combination of crystalline bulk semiconductors with 2D crystals are identified as promising heterogeneous structures for new optoelectronic applications. The direct integration of III–V semiconductors on 2D materials is very attractive to make practical devices but the preservation of the intrinsic properties of the underlying 2D materials remains a challenge. In this work, we study the direct epitaxy of self-organized GaN crystals on graphene. We demonstrate that severe metal–organic chemical vapor deposition growth conditions of GaN (chemically aggressive precursors and high temperatures) are not detrimental to the structural quality and the charge carrier mobility of the graphene base plane. Graphene can therefore be used both as an efficient sensitive material and as a substrate for GaN epitaxy to make a self-assembled UV photodetector. A responsivity as high as 2 A W–1 is measured in the UV-A range without any further postprocessing compared to simple deposition of contact...

Incorporation of indium into ε-gallium oxide epitaxial thin films grown via mist chemical vapour deposition for bandgap engineering

Abstract: Epitaxial e-gallium oxide (Ga2O3) thin films incorporated with In were successfully grown by mist chemical vapour deposition (CVD) on c-plane sapphire substrates for bandgap tuning. In was successfully incorporated into epitaxial e-(InxGa1−x)2O3 films at an In composition of x = 0.2 without inducing phase separation. Phase separation originated from the (400) bixbyite structure of (InxGa1−x)2O3 when x > 0.2. The solubility limit of In incorporated into e-Ga2O3 on sapphire substrates via mist CVD was therefore x = 0.2. Transmission electron microscopy measurements revealed that e-(InxGa1−x)2O3 consisted of polycrystalline phases observed in the interface of the sapphire substrate and e-phases located above the polycrystalline phase. The pole figure of e-(InxGa1−x)2O3 thin films revealed that the epitaxial relationship between the e-(InxGa1−x)2O3 thin film and the α-Al2O3 substrate is (001) e-(InxGa1−x)2O3 [130]||(0001) α-Al2O3 [11−20]. The optical bandgap of the e-(InxGa1−x)2O3 thin films was tuned from 4.5 to 5.0 eV without inducing phase separation.

Van der Waals epitaxy of two-dimensional single-layer h-BN on graphite by molecular beam epitaxy: electronic properties and band structure

Abstract: We report on the controlled growth of h-BN/graphite by means of molecular beam epitaxy. X-Ray photoelectron spectroscopy suggests the presence of an interface without any reaction or intermixing, while the angle resolved photoemission spectroscopy (ARPES) measurements show that the h-BN layers are epitaxially aligned with graphite. A well-defined band structure is revealed by ARPES measurements, reflecting the high quality of the h-BN films. The measured valence band maximum located at 2.8 eV below the Fermi level reveals the presence of undoped h-BN films (band gap 6 eV). These results demonstrate that, although only weak van der Waals interactionsare present between h-BN and graphite, a long range ordering of h-BN can be obtained even on polycrystalline graphite via van der Waals epitaxy, offering the prospect of large area, single layer h-BN.

Direct Growth of III–V/Silicon Triple-Junction Solar Cells With 19.7% Efficiency

Abstract: Monolithic multi-junction solar cells made on active silicon substrates are a promising pathway for low-cost high-efficiency devices. We present results of GaInP/GaAs/Si triple-junction solar cells, fabricated by direct growth on silicon in a metal–organic vapor phase epitaxy reactor using a GaAs y P1- y buffer structure to overcome the lattice mismatch between Si and GaAs. A low-temperature (750 °C) Si surface preparation process and a SiN x diffusion barrier at the rear side have been implemented to maintain the minority carrier lifetime in the Si bottom cell. Conversion efficiencies up to 19.7% have been achieved under AM 1.5g spectral conditions. The cells are compared with identical GaInP/GaAs dual-junction solar cells grown on bulk GaP and GaAs substrates to identify loss mechanisms. Subcell electrical characterization using electroluminescence reveals a significant voltage loss of the III–V subcells on Si, compared with the same structures grown on GaP or GaAs. Electron channeling contrast imaging of the metamorphic GaAs y P1- y buffer shows a three times higher threading dislocation density on Si (1.4 × 108 cm−2) than on GaP substrates, and atomic force microscopy shows holes in the GaAs y P1- y buffer on Si that are not observed on GaP. Approaches to reach lower defect densities for the III–V layers on silicon are discussed.

Effect of thermal annealing on AlN films grown on sputtered AlN templates by metalorganic vapor phase epitaxy

Abstract: To obtain low-dislocation-density c-plane AlN on sapphire, we have studied the annealing of AlN films at 1650 °C. We prepared an AlN film with a thickness of 20 nm by radio-frequency (RF) sputtering, on which an AlN epilayer with a thickness of 280 nm was grown by metalorganic vapor phase epitaxy (MOVPE) at different growth temperatures. Finally, the AlN film on sapphire was annealed at 1650 °C. The full width at half maximum (FWHM) of the X-ray rocking curve (XRC) for AlN(0002) was approximately 50 arcsec for all samples, whereas that for AlN() significantly decreased from 6500 to 350 arcsec after thermal annealing. A surface morphology with atomic steps and a terrace structure was clearly observed after thermal annealing. From these results, we concluded that a high-quality AlN film can be obtained by annealing a stacking structure of MOVPE-grown AlN (buffer layer)/sputtered AlN (nucleation layer)/sapphire substrate.

229 nm UV LEDs on aluminum nitride single crystal substrates using p-type silicon for increased hole injection

Abstract: AlGaN based 229 nm light emitting diodes (LEDs), employing p-type Si to significantly increase hole injection, were fabricated on single crystal bulk aluminum nitride (AlN) substrates. Nitride heterostructures were epitaxially deposited by organometallic vapor phase epitaxy and inherit the low dislocation density of the native substrate. Following epitaxy, a p-Si layer is bonded to the heterostructure. LEDs were characterized both electrically and optically. Owing to the low defect density films, large concentration of holes from p-Si, and efficient hole injection, no efficiency droop was observed up to a current density of 76 A/cm2 under continuous wave operation and without external thermal management. An optical output power of 160 μW was obtained with the corresponding external quantum efficiency of 0.03%. This study demonstrates that by adopting p-type Si nanomembrane contacts as a hole injector, practical levels of hole injection can be realized in UV light-emitting diodes with very high Al composit...

Water splitting to hydrogen over epitaxially grown InGaN nanowires on a metallic titanium/silicon template: reduced interfacial transfer resistance and improved stability to hydrogen

Abstract: Water splitting using InGaN-based photocatalysts may make a great contribution to future renewable energy production systems. Among the most important parameters that need to be optimized are those related to substrate lattice-matching compatibility. Here, we directly grow InGaN nanowires (NWs) on a metallic Ti/Si template, for improving the water splitting performance compared to a bare Si substrate. The open circuit potential of the epitaxially grown InGaN NWs on metallic Ti was almost two times higher than when directly grown on the Si substrate. The interfacial transfer resistance was also reduced significantly after introducing the metallic Ti interlayer. An applied-bias-photon-to-current conversion efficiency of 2.2% and almost unity faradaic efficiency for hydrogen generation were achieved using this approach. The InGaN NWs grown on Ti showed improved stability for hydrogen generation under continuous operation conditions, when compared to those grown on Si, emphasizing the role of the semiconductor-on-metal approach in enhancing the overall efficiency of water splitting devices.

Sources of carrier compensation in metalorganic vapor phase epitaxy-grown homoepitaxial n-type GaN layers with various doping concentrations

Abstract: The source of carrier compensation in metalorganic vapor phase epitaxy (MOVPE)-grown n-type GaN was quantitatively investigated by Hall-effect measurement, deep-level transient spectroscopy, and secondary ion mass spectrometry. These analysis techniques revealed that there were at least three different compensation sources. The carrier compensation for samples with donor concentrations below 5 × 1016 cm−3 can be explained by residual carbon and electron trap E3 (E C − 0.6 eV). For samples with higher donor concentrations, we found a proportional relationship between donor concentration and compensating acceptor concentration, which resulted from a third source of compensation. This is possibly due to the self-compensation effect.

Role of gallium diffusion in the formation of a magnetically dead layer at the Y 3 Fe 5 O 12 /Gd 3 Ga 5 O 12 epitaxial interface

Abstract: We have clarified the origin of a magnetically dead interface layer formed in yttrium iron garnet (YIG) films grown at above 700 \ifmmode^\circ\else\textdegree\fi{}C onto a gadolinium gallium garnet (GGG) substrate by means of laser molecular beam epitaxy. The diffusion-assisted formation of a Ga-rich region at the YIG/GGG interface is demonstrated by means of composition depth profiling performed by x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and x-ray and neutron reflectometry. Our finding is in sharp contrast to the earlier expressed assumption that Gd acts as a migrant element in the YIG/GGG system. We further correlate the presence of a Ga-rich transition layer with considerable quenching of ferromagnetic resonance and spin wave propagation in thin YIG films. Finally, we clarify the origin of the enigmatic low-density overlayer that is often observed in neutron and x-ray reflectometry studies of the YIG/GGG epitaxial system.