Lattice curvature induced substrate X-ray line broadening in InGaP/GaAs heterostructures

The interfacial coherency of InGaP/GaAs heterostructure wafers grown by the metal-organic chemical vapor deposition technique is examined and its effects on the X-ray line broadening of the GaAs substrate are investigated. Lattice mismatches are measured using both (400) symmetric and {511} asymmetric reflections. The strain-free chemical lattice misfit and the elastic strain are also calculated. The X-ray full width at half maximum (FWHM) of the substrate is measured, and its dependence on the degree of lattice mismatch is found. In order to understand this observation, measurements of lattice curvature are carried out using the automatic Bragg angle control method. It is found that the radius of curvature varies with the elastic strain and the substrate FWHM. Using the results obtained, the misfit stress is also determined. Various contributions to the substrate line broadening are separated out. Calculated line widths are shown to be in good agreement with measured values. It is thus concluded that the primary factor affecting the X-ray line width of the substrate is misfit stress induced lattice curvature. The results presented demonstrate that interfacial coherency is of major importance in influencing the structural properties of InGaP/GaAs heterostructures through elastic strain and lattice curvature.