Role of thin InP cap layer and anion exchange reaction on structural and optical properties of InAs quantum dots on InP (001)

Structural and optical properties of InAs quantum dots (QDs) or InP (001) substrates were studied during low-pressure metalorganic chemical vapor deposition (MOCVD), using photoluminescence (PL) and transmission electron microscopy (TEM). To clarify how the properties of QDs can be controlled through surface reactions, two kinds of source gas supply sequence were compared. With a double-capping procedure, PL changed into a series of multiple peaks arising from different integer numbers of InAs monolayers. PL studies revealed that the spectra of double-capped samples are not affected by a long phosphine (PH3) exposure during growth interruption, indicating reactions relevant to arsenic (As)/phosphorus (P) exchange at the QD surface is self-limited. TEM observations clarified that the shape of double-capped QDs dramatically changes into a thin plate-shape with flat upper and lower interfaces while the density of QDs remains unchanged. In contrast, under the normal capping procedure, the structural and optical properties on QDs are sensitive to the duration of PH3 before InP capping. Results suggest that As/P exchange is not self-limiting, leading to decreased QD density and,enlarged QD diameters. We discuss the role the thin InP initial cap layer plays in the anion exchange reaction during the double-capping procedure and the technical importance of controlling the emission wavelength of QDs. 0 2005 American Vacuum Society.