X-ray Coherent Scattering on GaP/Si for III-V Monolithic Integration on Silicon

Abstract : GaP, quasi-lattice matched to Si, allows growth of low defect density III-V/Si pseudosubstrates [1]. However, Antiphase boundaries (APB) likely appear and must be avoided. In this context, X-ray nanodiffraction and Bragg coherent diffraction imaging (BCDI) have been used as non-destructive techniques for local characterization of APB configuration [2]. Different GaP/Si nanolayers were studied at ID01/ESRF with an 8 keV coherent xray beam. Here a 140nm thick GaP presents annihilated APB (less than 3/m emerging APB). Bragg geometry ptychography of the APB has been attempted using (002) GaP weak reflection. This shows a peak splitting, characteristic of a heterogeneous APB density. But a still too high defect density precludes successful phase retrieval imaging. Two-dimensional fast mapping (kmap) [3] over the (004) and the (002) reflections shows for different regions of integrated intensities (ROI) (Fig. 1a) weak (Bragg maximum -0.5° on rocking angle) and strong scattering conditions (Fig. 1b and 1c respectively). As shown fig. 1b), the weak scattered intensity in ROI1, exhibits contrast lines oriented along both [1 1 0] and [-1 1 0] crystallographic directions. This contrast corresponds to regions of high tilt, surrounding misfit dislocations [3]. Strong scattering conditions performed on the (004) (Fig. 1c) and the (002) Bragg reflections present a quite different contrast with large spotty regions. We believe that this anisotropic contrast is due to weak tilt/strain, associated to the APD annihilation process.1. Y. P. Wang et al., Appl. Phys. Lett. 107, 191603 (2015).2. S. Labat et al., ACS Nano 9, 9210 (2015).3. M. H. Zoellner et al., ACS Appl. Mater. Interfaces 7, 9031 (2015).