GROWTH OF METASTABLE GE1-XSNX/GE STRAINED-LAYER SUPERLATTICES ON GE(001)2X1 BY TEMPERATURE-MODULATED MOLECULAR-BEAM EPITAXY

Single-crystal metastable diamond-structure Ge1-xSnx/Ge strained-layer superlattices (SLS) with x up to 0.24 (the equilibrium solid solubility of Sn in Ge is < 0.01) have been grown on Ge(001) 2 X 1 substrates using temperature-modulated molecular-beam epitaxy with maximum growth temperatures T-s less than or equal to 150 degrees C. In situ reflection high energy electron diffraction combined with postdeposition high-resolution x-ray diffraction (HR-XRD) and cross-sectional transmission electron microscopy results show that the Ge1-xSnx(001) 2 X 1 alloy and Ge(001) 2 X 1 spacer layers are commensurate. In fact, the alloy layers are essentially fully strained with an average in-plane lattice constant mismatch of (1 +/- 2) X 10(-5) and an average tetragonal strain in the growth direction of (1.39 + /- 0.03) x 10(-2) as determined from HR-XRD reciprocal-space lattice maps obtained using asymmetric (113) reflections. omega broadening of the zero-order SLS peak was only 30.1 are sec FWHM, indicating that the degree of mosaicity in these structures is negligible. The intensities and positions of the satellite reflections and finite-thickness interference fringes in HR-XRD 004 rocking curve omega-2 theta scans are in good agreement with simulated patterns obtained using a dynamical scattering model. (C) 1995 American Institute of Physics.