Transmission electron microscopy study of the InP/InGaAs and InGaAs/InP heterointerfaces grown by metalorganic vapor-phase epitaxy

Abstract

InP/InGaAs and InGaAs/InP interfaces in heterostructures grown by metalorganic vapor-phase epitaxy (MOVPE) have been studied by transmission electron microscopy (TEM). Cross-sectional TEM 002 dark field images of the direct (InP–InGaAs) and inverted (InGaAs–InP) interfaces revealed a great difference in abruptness. Whereas the direct interface is always well defined and flat, the inverted one is compositionally graded and shows surface undulations. InP–InGaAs heterostructures were studied for different layer thicknesses and phosphine flow rates. The results indicate that this effect originates more from the substitution of arsenic by phosphorus atoms in subsurface InGaAs monolayers rather than from As carryover to the InP layer. The strong As–P exchange observed over several InGaAs monolayers is related to the large difference in chemical bond strength between Ga–As and Ga–P. This is supported by comparison with InP/InAlAs/InP and InP/In1−xGaxAsyP1−y/InP (0.1<x<0.4) heterostructures. The inverted InAlAs/InP interface is much more abrupt than the InGaAs/InP one and does not show any surface undulations. Furthermore, the In1−xGaxAsyP1−y/InP interface surface undulations increase with x composition. These results, valid for our experimental configuration, indicate that MOVPE grown InGaAs/InP interfaces can be improved by using very low hydride flow during the switching sequence.