Selective area chemical beam epitaxy is used to fabricate submicron [100]-oriented InP ridges with well-defined, defect-free (011) sidefacets and (001) tops. Following the deposition of two monolayers of InAs on such nanotemplates and subsequent capping with InP, photoluminescence spectra show for wider ridges strong emission from a thin InAs, quantum well and, as the ridge width is reduced, a gradual appearance of a quantum dot emission at lower energy. The method allows continuous tuning on a given sample in a single growth run of both the quantum dot density and the emission wavelength. The result is a consequence of adatom diffusion from the ridge sidefacets onto the top (001) facet, which increases the amount of InAs beyond the critical thickness for three-dimensional nucleation to occur. Compared with growth on planar InP(001) substrates, InAs self-assembled quantum dots grown on these nanotemplates are more uniform as revealed by a twofold reduction in emission linewidth at 4 K.