Mosaic Spread of the Heteroepitaxial Structures from Renninger Scan
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MOSAIC SPREAD OF THE HETEROEPITAXIAL STRUCTURES FROM RENNINGER SCAN
S.L. MORELHAO AND L.P. CARDOSO INSTITUTO DE FfSICA - UNICAMP, CP 6165 13081, CAMPINAS, SP, BRAZIL
ABSTRACT In this work, a method of obtaining mosaic spread of the heteroepitaxial structures using Renninger scan (RS) peak profiles is reported. A simulation program was developed in order to account for the influence of the wavelengths, incident beam divergence, sample mosaic spread (layer and substrate) in the profile of the RS peaks. Surface three beam multiple diffraction cases with a forbidden or even very weak primary reflections are used to provide simpler intensity expressions and high intensity in RS. GaAs/Si samples have been analyzed as an application of this method.
INTRODUCTION
The multiple diffraction (MD) phenomenon is systematically produced by rotating a single crystal around the normal to the crystalline planes (called primary), usually parallel to the sample surface, while the diffracted beam is monitored. By rotation (0 is the rotation angle), several planes (called secondary) within the single crystal with any kind of orientation are simultaneously diffracting with the primary. Their contributions appear in the Iprimary x 4 pattern called Renninger Scan (RS) [1]. The interactions among the primary and the several secondary reflections are established through the coupling reflections. The secondary beams which are diffracted parallel to the primary planes (surface secondary beams) are very important since they should provide high intensity in the layer RS (2] and they also represent the simpler multiple diffraction case to be analyzed. Scans for heteroepitaxial structures can present contributions from the layer together with those from the layer/substrate interactions called hybrid (3], which occurrence in a RS has already been reported [4]. In this work, the developed simulation program is applied to GaAs/Si structures to provide the layer (01) and the substrate (Ts) mosaic spreads. It accounts for the normal layer MD path (secondary and coupling reflections in the layer lattice - LL peak) and also the hybrid MD path (secondary in the substrate lattice and coupling in the layer lattice - SL peak).
RENNINGER SCAN PEAK PROFILE FOR MOSAIC CRYSTALS
The incident beam in the reciprocal space is represented by the double wave vector r = -2k., where Irl = R = 2/A. The primary beam direction is represented by r' being go the primary reciprocal vector whereas the beam diffracted by the secondary planes (represented by gV) has its. direction given by rl. The coupling vector g 2 = go - g1 scatters the secondary beam towards the primary direction. Fig. 1, shows the geometry involved in a Mat. Res. Soc. Symp. Proc. Vol. 262. @1992 Materials Research Society
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Primary beam
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secondary beam
Figure 1: Geometry of a three beam MD case. The incident beam is simultaneously diffracted by the primary and secondary planes. In turn, the secondary beam is diffracted by the coupling towards the primary direction.
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