Peculiarities of strain relaxation in linearly graded InxGa1−xAs/GaAs(001) metamorphic buffer layers grown by molecular beam epitaxy

This paper presents a comprehensive study of structural, optical and electrical properties of heterostructures with linearly graded InxGa1−xAs metamorphic buffer layers (MBLs) grown by molecular beam epitaxy on GaAs (001) substrates. The low density of threading dislocations (well below 106 cm−2) in 1-μm-thick In0.3Ga0.7As layers grown atop of the linearly graded InxGa1−xAs/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.