Comparison of X-ray diffraction methods for determination of the critical layer thickness for dislocation multiplication

We present a comparison of x-ray diffraction methods for the determination of the critical layer thickness for dislocation multiplication in mismatche d heteroepitaxy. The conventional x-ray diffraction method for determinatio n of the critical layer thickness is based on the direct observation of the lattice relaxation in measurements of strain (the "strain method"). An ind irect method is based on the observation of the x-ray rocking curve broaden ing by the threading dislocations, which are introduced concurrently with m isfit dislocations (the "full width at half maximum (FWHM) method"). For th is study, we have applied both methods to ZnSe grown on GaAs (001)by metalo rganic vapor phase epitaxy (MOVPE). We have compared the resolution of the two x-ray diffraction methods both theoretically and experimentally for the case of 004 reflections using Cuk alpha(1) radiation. Theoretically, we ha ve shown that in this case the FWHM method is 2.6 times more sensitive to r elaxation than the strain method. This conclusion is supported by our exper iments, in which we determined a critical layer thickness value of 140 nm b y the FWHM method, compared to 210 nm as determined by the strain method.