X-RAY STUDY OF LATERAL STRAIN AND COMPOSITION MODULATION IN AN ALGAASOVERLAYER INDUCED BY A GAAS LATERAL SURFACE GRATING

A lateral surface grating has been prepared by holographic photolithog raphy followed by wet chemical etching on a slightly misaligned GaAs [ 001] substrate. The structural parameters were investigated before and after thermal annealing by triple-axis high resolution x-ray diffract ion (HRXRD) and scanning electron microscopy (SEM). In particular HRXR D was used to collect reciprocal space maps providing periodicity and shape of the grating. After overgrowth of the free standing nanostruct ure with AlxGa1-xAs the HRXRD technique fails. Only first order gratin g truncation rods remain in the (004) HRXRD map. They disappear comple tely running asymmetric reflections. On the other hand SEM at the clea vage plane reveals the perfection of the overgrowth process and the sm oothness of the sample surface. Thus nondestructive analysis of the bu ried lateral nanostructure was performed by triple-axis x-ray grazing incidence diffraction using synchrotron radiation. This method is excl usively sensitive to the lateral strain profile and provides the possi bility of depth resolution. Using two complementary in-plane reflectio ns we found lateral strain modulation within the GaAlAs overlayer acco mpanied by a compositional modulation with the same period as the grat ing itself. This periodicity still appears close below the sample surf ace. (C) 1998 American Institute of Physics.