Determination of the anharmonicity constant of GaAs by means of the Bijvoet relation of the weak (666) reflection

Abstract

As a result of the influence of anomalous dispersion the weak (hhh) and (hhh) reflections of the zinc blende structure differ from each other. At large scattering vectors this difference, described by the Bijvoet relation B, depends solely on the size of the anharmonic force constant /3. It can be determined by measuring B near the K-absorption edge of any constituent. This experiment was performed for the (666) and (666) reflections of GaAs between A = 0.90 and 0.97 A, using synchrotron radiation. Outside the extended X-ray absorption fine-structure spectroscopy region the integrated intensities decrease in a different manner with increasing A for both reflections measured at 'umweganregung' free azimuthal positions. Under the assumption of/3Oa = --/3As and using the measured wavelength dependence of B, the anharmonicity constant is evaluated to /3 = -1.75 (0.15) × 10-17j •-3 which is nearly the same as that for germanium.