STRUCTURAL AND OPTICAL INVESTIGATION OF INASXP1-X INP STRAINED SUPERLATTICES/

We report a complete characterization of InAsxP1-x/InP (0.05<x<0.,59) superlattices epitaxially grown by low pressure metalorganic chemical vapor deposition and by chemical beam epitaxy, Samples were obtained b y both conventional growth procedures and by periodically exposing the just-grown InP surface to an AsH3 flux. Using the latter procedure, v ery thin InAsxP1-x/InP layers (10-20 Angstrom) are obtained by P<->As substitutions effects, Arsenic composition of the so obtained layers d epends both on AsH3 flux intensity and exposure times, Samples have be en characterized by means of high resolution x-ray diffraction, high r esolution transmission electron microscopy, 3 IC photoluminescence, an d extended x ray absorption fine structure spectroscopy, The combined use of high resolution x-ray diffraction and of 4 K photoluminescence, with related simulations, allows us to predict both InAsP composition and width, which are qualitatively confirmed by electron microscopy. Our study indicates that the effect of the formation of thin InAsP lay ers is due to the as incorporation onto the InP surface exposed to the As flux during the AsH3 exposure, rather than the residual As pressur e in the growth chamber during InP growth, Arsenic K-edge extended x-r ay absorption fine structure analysis shows that the first shell envir onment of As at these interfaces is similar to that found in bulk InAs xP1-x, alloys of similar composition, In particular we measure an almo st constant As-in bond length (within 0.02 Angstrom), independent of A s concentration; this confirms that epitaxy with InP is accompanied by local structural distortions, such as bond angle variations, which ac commodate the nearly constant As-In bond length. In our investigation we characterize not only very high quality heterostructures but also s amples showing serious inter-face problems such as nonplanarity and/or a consistent chemical spread along the growth axis, In the study pres ented here we thus propose a general method, based on several independ ent techniques, for the characterization of the interface quality of s emiconductor superlattices, (C) 1998 American Institute of !Physics. [ S0021-8979(98)06602-X].