Structural characterization of InAlAsSb/InGaAs/InP heterostructuresfor solar cells

Abstract

tIn this work, we have characterized by transmission electron microscopy techniques the structural prop-erties of InAlAsSb/InGaAs/InP heterostructures, with target applications in high efficiency solar cells.Previous photoluminescence (PL)1analysis suggested the existence of compositional fluctuations inthe active layer of these heterostructures. 220 bright field (BF)2diffraction contrast micrographs haverevealed strong strain contrast in the InGaAs buffer layer, related to the existence of these compositionalfluctuations. The effect of a decomposed buffer on the growth of the InAlAsSb layer has been analyzedthrough the simulation of the strain fields in the heterostructure using the finite elements method (FEM).3These simulations have shown that the strain in the buffer layer due to the compositional fluctuations onlyaffects the first few nm of the InAlAsSb layer. The analysis by aberration corrected high angle annulardark field scanning transmission electron microscopy (HAADF-STEM)4and electron energy loss spec-troscopy (EELS)5of the composition of the InAlAsSb layer reveals that any compositional fluctuation isonly observed as an average effect, rather than in the form of clustering or atomically sharp transitions.The limitations of these techniques for the detection of small 3D compositional fluctuations are discussed.