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 solubili ty 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 reflect ion high energy electron diffraction combined with postdeposition high -resolution x-ray diffraction (HR-XRD) and cross-sectional transmissio n 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 l ayers are essentially fully strained with an average in-plane lattice constant mismatch of (1 +/- 2) X 10(-5) and an average tetragonal stra in in the growth direction of (1.39 + /- 0.03) x 10(-2) as determined from HR-XRD reciprocal-space lattice maps obtained using asymmetric (1 13) reflections. omega broadening of the zero-order SLS peak was only 30.1 are sec FWHM, indicating that the degree of mosaicity in these st ructures is negligible. The intensities and positions of the satellite reflections and finite-thickness interference fringes in HR-XRD 004 r ocking curve omega-2 theta scans are in good agreement with simulated patterns obtained using a dynamical scattering model. (C) 1995 America n Institute of Physics.