Influences of Interfacial Misfit Stress on Modulated Microstructures of InGaAsP / InP Heterostructures

Abstract

The misfit stresses of metallorganic chemical vapor deposition grown InGaAsP/InP heterostructure wafers were determined and their effects on the modulated mierostructures of InGaAsP epilayer were investigated. Lattice mismatches were measured using {511} asymmetric and (400) symmetric x-ray reflections. Elastic strains were obtained from the parallel mismatches and were used for determining the misfit stresses. Transmission electron microscopy results showed the presence of the modulated mierostructures (spinodal decomposition) in the epilayer. It was found that the modulation periodicity varies with the lattice mismatches. To investigate this observation, the interaction elastic energy induced by misfit stress was derived and used to explain the experimental results. Good agreement was obtained between the measured and calculated modulation wavelength. Also, contributions from the composition and misfit stress to variation of modulation periodicity were separated out, and the misfit stress was found to have the larger contribution. Thus, it is concluded that the interfaeial coherency and misfit stress have large influences on the mierostructures of the InGaAsP epilayer, particularly on the modulation wavelength.There has been extensive interest in In~ xGaxASyPl_y quaternary epitaxial layers lattice matched to InP substrate. Such heterostructures are of significance for various devices such as laser diodes, light-emitting diodes, and photodiodes. This system is important because energies of the direct bandgap cover the range where the optical losses in silica-based optical fibers reach a minimum. 1 One main requirement in the fabrication of perfect heterostruetures is the maintenance of coherency of the interface between the epilayer and the substrate. When the lattice is mismatched, misfit stress is developed. Lattice mismatch and misfit stress have been shown to have a large influence on physical properties such as photoluminescence (PL) and electrical properties of these devices. ~ It is well accepted that a miscibility gap exists in the InGaAsP/InP system. 3 Since the first report of immiscibility of this system, the observation and the interpretation of phase separation in this alloy have been interesting and controversial subjects. Attention has been focused mainly on comprehension of the origin of this phenomenon 4-6 and on its resulting effects on the optoeleetronic and structural properties] Little attention, however, has been paid to the influence of stress field on the microstruetures of this alloy. Since the misfit stress is always present in compound semiconductor multilayered systems, it is fun damentally significant to understand its effects on the microstructure, especially on the composition modulation wavelength. The most noteworthy study made on the influence of misfit stress on the mierostructure is the substrate-indueed stabilization theory developed by deCremoux. ~ This theory, however, has been used only to justify the existence of modulated structures, and is not expected to yield...