Required skills: basic knowledge of crystallography and x-ray characterization, ability in programming language

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Required skills: basic knowledge of crystallography and X-ray characterization, ability in programming language.
Sujet/Subject : Modelisation of antiphase domains in GaP/Si nanolayers and X-ray diffraction
Our laboratory is highly skilled in molecular beam epitaxy (MBE) growth of InAs QDs on InP, for laser devices with potential applications telecommunication (emission at
1.55m). In order to extend these applications to laser emission on Si for very large
scale integration, GaP (III-V) growth on silicon is studied. Several types of defects are observed on such layer and are detrimental for applications. Amongst them APB and thus anti-phase domains (APD) are difficult to avoid since they are due to the intrinsic nature of the interface. The fig. 1a presents a typical APD above a single monolayer (ML) Si step (indeed 1 GaP ML corresponds to 2 Si ML). As shown on figure 1b, a broad peak is observed in X-ray diffraction around the (002) “antiphase” reflection. This feature can be interpreted in term of distribution of APD included in a coherent GaP matrix.

The aim of this training period is to modelize the atomic positions in the vicinity of an APD, taking into account two things :

i) the lattice mismatch of GaP/Si and the strain of positions induced by Si steps

ii) the strain induced by the presence of different atomic bounds at the APB and at GaP/Si interface. Depending on traing period duration and affinity, the candidate could participate to experimental X-ray acquisitions.

This model will be used to simulate the X-ray diffraction diagrams in interaction with experimental ones. This will increase the characterization power of X-ray diffraction and will have a large impact in the success of a ANR project : GaPhoSiX.

a)	b)
Fig. 1 a : Scheme of APD on Si monostep b :X-ray rocking curves around (004) and (002) of GaP.