Raman spectra of GaAs with ultrathin InAs layers inserted are measured and interpreted by comparing with spectra calculated based on the linear-chain model. The samples are grown by molecular-beam epitaxy, and the InAs layer thickness is varied from 2 ML (monolayers) to 10 ML. Both (001)-oriented and slightly misoriented substrates are used. From the transmission electron micrograph observation, it is found that the introduction of misfit dislocations is delayed on the misoriented substrate compared with the oriented substrate. When the InAs thickness is less than 6 ML, optical phonon modes in InAs are not observed. This is due to coupling of the InAs vibration to the vibration of the GaAs host lattice. At a thickness of 6 ML, the InAs longitudinal-optical mode begins to appear for the sample on the oriented substrate, but it is still unobservable for that on the misoriented substrate. Thus, the intensity of the InAs mode is stronger in a more heavily dislocated structure. This is because the InAs vibration is decoupled from the host GaAs vibration owing to dislocations at the heterointerfaces.

• Received 2 November 1994

DOI:https://doi.org/10.1103/PhysRevB.51.13231