Growth of metastable Ge1−xSnx/Ge strained layer superlattices on Ge(001)2×1 by temperature-modulated molecular beam epitaxy

Abstract

Single‐crystal metastable diamond‐structure Ge_1−xSn_x/Ge strained‐layer superlattices (SLS) with x up to 0.24 (the equilibrium solid solubility of Sn in Ge is T_s≤150 °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 Ge_1−xSn_x(001)2×1 alloy and Ge(001)2×1 spacer layers are commensurate. In fact, the alloy layers are essentially fully strained with an average in‐plane lattice constant mismatch of (1±2)×10⁻⁵ and an average tetragonal strain in the growth direction of (1.39±0.03)×10⁻² as determined from HR‐XRD reciprocal‐space lattice maps obtained using asymmetric (113) reflections. ω broadening of the zero‐order SLS peak was only 30.1 arc 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 ω‐2θ scans are in good agreement with simulated patterns obtained using a dynamical scattering model.