DIFFUSE-X-RAY SCATTERING OF MISFIT DISLOCATIONS AT SI1-XGEX SI INTERFACES BY TRIPLE-CRYSTAL DIFFRACTOMETRY/

Heterostructure Si1-xGex layers on (001)Si substrates with different d egrees of relaxation R, ranging from the nearly pseudomorphic state to the nearly relaxed state (R similar to 0.8), were characterized by di ffuse x-ray scattering measurements. The lattice constants a(perpendic ular to) and a(parallel to), and from these the Ge content x, the rela xation A, and misfit dislocation density D-d, were determined by singl e crystal diffractometry. The thickness of the SiGe layers was measure d in the as-grown state by double crystal diffractometry. A standard t riple crystal x-ray diffractometer was used to analyze the diffuse x-r ay scattering (DXS) intensity by rotation of the analyzer crystal (Del ta Theta) at a fixed sample position (alpha). The intensities were mea sured around the 004 reciprocal lattice point of the Si substrate usin g a wide open counter and a wide range of rotation angle (Delta Theta) for the analyzer crystal, The diffuse scattering increases steeply wi th increasing dislocation density up to a critical value of D-d approx imate to 5 x 10(4) cm(-1). Then it reaches saturation and decreases sl owly as D-d increases. This behavior can be cm explained by the superp osition of the strain fields of neighboring dislocations above a criti cal density, so that only the heavily distorted regions near the dislo cation core participate in scattering. This is confirmed by the fact t h-dt the DXS measured for different alpha values follows The Stokes-Wi lson scattering (I(DXS)proportional to q(-4); q being the scattering v ector). We show that: the diffuse scattering technique is a very sensi tive tool to detect relaxation at relatively low levels of dislocation densities , where diffractometric techniques that measure the lattice constants are D-d less than 5x10(4) cm(-1), near their resolution lim its. (C) 1997 American Institute of Physics.