Contents lists available at ScienceDirect Journal of Crystal Growth journal homepage: www.elsevier.com/locate/jcrysgro Peculiarities of strain relaxation in linearly graded In x Ga 1−x As/GaAs(001) metamorphic buffer layers grown by molecular beam epitaxy S.V. Sorokin ⁎ , G.V. Klimko, I.V. Sedova, A.A. Sitnikova, D.A. Kirilenko, M.V. Baidakova, M.A. Yagovkina, T.A. Komissarova, K.G. Belyaev, S.V. Ivanov Ioffe Institute, Politekhnicheskaya Street 26, St. Petersburg 194021, Russia ARTICLE INFO Communicated by Klaus H. Ploog Keywords: A1. Crystal structure A1. Stresses A1. X-ray diffraction A3. Molecular beam epitaxy B2. Semiconducting III–V materials ABSTRACT This paper presents a comprehensive study of structural, optical and electrical properties of heterostructures with linearly graded In x Ga 1−x As metamorphic buffer layers (MBLs) grown by molecular beam epitaxy on GaAs (001) substrates. The low density of threading dislocations (well below 10 6 cm −2 ) in 1-μm-thick In 0.3 Ga 0.7 As layers grown atop of the linearly graded In x Ga 1−x As/GaAs MBLs has been confirmed by using transmission electron microscopy (TEM). X-ray diffraction (XRD) data demonstrate good agreement between the experimentally measured In step-back and its calculations in the frames of existing models. Combining the XRD reciprocal space maps (RSM) of the structures and the spatially-resolved selective area electron diffraction measurements by cross-sectional TEM in depth-profiled RSM diagrams allowed direct visualization of the strain relaxation dynamics during the MBL growth. Strong effect of the azimuth angle and the value of an unintentional initial miscut of nominally (001) oriented GaAs substrate on the strain relaxation dynamics was observed. 1. Introduction Heteroepitaxy of semiconductor alloys has opened up new oppor- tunities for designing various device heterostructures containing lattice-mismatched strained layers. To achieve the best structural quality of a heterostructure the epitaxial growth should proceed on substrates lattice-matched to the main body of the heterostructure. Because of the discreteness of the lattice constants (a) of the III–V binaries (minimum Δa/a step is ~3.3–3.5%) commonly used as substrates, the studies aimed at creating low-defect-density III–V templates with intermediate a values have been attracting great attention for many years. The employing of a metamorphic growth concept using compositionally graded alloy layers [1–3] allowed one to improve significantly characteristics of heterostructures grown on lattice-mismatched substrates as well as extend the functionality of semiconductor devices grown on GaAs substrates by molecular beam epitaxy (MBE) [4–6]. The compositionally graded layers are widely used in heteroepitax- ial systems since late 60 s of the last century [7], and the In x Ga 1−x As/ GaAs system has been the most extensively studied one. To reduce the density of threading dislocations (TDs) after the metamorphic buffer layer (MBL), being a key parameter characterizing the MBL structures, different designs of the In x Ga 1−x As/GaAs MBLs (different grading profiles and grading rates) were employed, as well as various MBE growth conditions (low [8] and high growth temperatures [9,10], using of different dopants during MBL growth [8,11,12], utilizing of As 2 and As 4 fluxes [13] etc.) were explored. Based on both experimental data and theoretical concepts, several models of strain relaxation in compositionally graded MBLs have been developed [13–20]. However, since the dislocation dynamics as well as the processes of stress relaxation in these structures have not been completely under- stood yet, while new factors affecting them appear, MBE growth of the MBLs is still attributed to a category of art. X-ray diffraction (XRD) reciprocal space mapping (RSM) is com- monly used for characterization of MBLs see e.g. [21,22]. Due to the difficulty in correlating the RMS angular positions to a certain depth of MBL Chauveau et al. [23] used TEM to check the MBL thicknesses. Based on the TEM thickness and RSM data they calculated and plotted depth profiles of residual strain in both [110] and [1–10] directions in the linearly graded InAlAs MBLs with a step of ~50 nm. The depth profiles of lattice mismatch, residual strain, crystallographic tilt, and the rocking curve full-width-at-half-maximum (FWHM) for meta- morphic In x Al 1−x As buffer layers grown on GaAs substrates were also obtained from the XRD RSM [24]. The tilt angle was directly obtained from the 004 RSM data as a function of composition by assuming the monotonous composition variation across the sample thickness. http://dx.doi.org/10.1016/j.jcrysgro.2016.09.071 Received 17 August 2016; Received in revised form 27 September 2016; Accepted 28 September 2016 ⁎ Corresponding author. E-mail address: sorokin@beam.ioffe.ru (S.V. Sorokin). Journal of Crystal Growth 455 (2016) 83–89 Available online 29 September 2016 0022-0248/ © 2016 Elsevier B.V. All rights reserved. MARK