STRAIN RELAXATION AND INTERDIFFUSION IN SI/SI1-XGEX STRAINED LAYER SUPERLATTICES

We have investigated the structural properties of Si/Si1-xGex multilayers using x-ray diffraction, x-ray reflection, and cross-sectional transmission electron microscopy. The structures consisted of 14-28 periods of thin (40-70 angstrom) Si1-xGex layers (0.4 less-than-or-equal-to x less-than-or-equal-to 0.7) with 180-280 angstrom Si spacers with 1-mu-m Si cap layers. The sample quality was engineered to range from defect-free to highly defective in order to assess the relative merits of the different analytical techniques. Electron microscopy provides information on layer thicknesses and the presence of extended defects, while the nondestructive x-ray techniques determine composition (chi(Ge) +/- 0.005), layer thickness (+/- 1 angstrom), heterointerface mixing (2.5 angstrom) roughness, < 10 angstrom grade), and strain relaxation (approximately 2%) in these structures. We show that multiple characterization techniques are required to study structural issues in Si/Si1-xGex strained layer superlattices.