Istituto dei materiali per l'elettronica ed il magnetismo     
Frigeri C., Attolini G., Bosi M., Pelosi C., Germini F. Composition determination of the interlayer at the inverted interfaces in InGaP/GaAs heterojunctions. In: BIAMS 2008 - BIAMS 2008, 9th International Workshop on Beam Injection Assessment of Microstructures in Semiconductors (Toledo (E), 29/06 - 03/07/ 2008). Abstract, pp. 111 - 111. J. Piqueras, Ed (eds.). Universidad Complutense, Madrid (E), 2008.
TEM in the (200) dark field (DF) mode was used in combination with high resolution X-ray diffraction (HRXRD) to determine the composition of the interlayer at the inverted interfaces in InGaP/GaAs heterojunctions The investigated samples were made of two InGaP/GaAs heterojunctions embedded between a GaAs buffer and an InGaP cap. They were grown by MOVPE at 600 C on (100) GaAs. The reagents were TMG, TMI and PH3 and AsH3 diluted (10%) in H2. The (200) DF observations were performed in the thinnest areas of the TEM specimen (thickness 8- 10 nm) so that the kinematical theory could be applied for the evaluation of the DF contrast. On the other hand, the experimental HRXRD rocking curves were simulated by using the dynamical theory. The GaAs and InGaP layers exhibited their expected (200) DF contrast except at the inverted GaAs-on-InGaP interface where a contrast darker than that of GaAs was detected indicating the presence of an extra interlayer there. No such interlayer was seen at the InGaP-on-GaAs direct interface. HRXRD results could be fit only assuming an extra interlayer at the inverted interface that turned out to have a negative (tensile) strain of -2x10-2 with respect to GaAs. Simulations of the (200) DF contrast for all possible compounds that may form at the inverted interface showed that only 3 compounds can account for the observed features of the interlayers, i.e., InxGa1-xAs1-yPy, GaAs1-yPy and InxGa1-xAs. The latter one must be excluded as it is always in compression to GaAs. The allowed compositions for the other 2 compounds determined by DF cover a quite large range for both InxGa1-xAs1-yPy and GaAs1-yPy. To restrict it use was made of the fact that the interlayer has a negative strain to GaAs of -2x10-2 in association with evaluation of the strain of InxGa1-xAs1-yPy or GaAs1-yPy with respect to GaAs as a function of their composition. It was thus seen that the interlayer at the inverted interface can be either GaAs0.45P0.55 or InxGa1-xAs1-yPy with 0
Subject Characterization
III-V compounds

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