High-resolution Electron Microscopy of GaInAsP: Implications for the study of interfaces and decomposition phenomena

The quaternary semiconducting compound GaxIn1-xAsyP1-y has important applications in optoelectronic devices, in the form of heterostructures and quantum wells. Lattice matching between two materials with a composition difference (Δx,Δy) is achieved if Δy≈2.2Δx. Furthermore, decomposition structures have been described in these compounds; the decomposition is expected to follow Δy≈=Δx (Fig. 1). In the present study the sensitivity of high-resolution electron microscope (HREM) images for these composition variations is investigated.GaxIn1-xAsyP1-y layers lattice-matched to InP (x=0, y=0) have been studied with HREM in [001] plan view specimens, and in and cross-sections. The experimental images were interpreted using image simulations. The observations can be summarized as follows: (1) Even small differences in composition between lattice-matched layers (Δx≈0.17, Δy≈0.37) lead to appreciable HREM-image contrast in cross-section specimens (Fig. 2). -orientations are less sensitive, but interfaces associated with Δx≈0.26, Δy≈0.56 still show good composition contrast (Fig. 3).