The two- (2D) to three-dimensional (3D) growth mode transition during the initial stages of growth of highly strained InGa1-xAs on GaAs is used to obtain quantum dot structures. Transmission electron micrographs (TEM) reveal that when the growth of InxGa1-xAs is interrupted exactly at the onset of this 2D-3D transition, dislocation-free islands (dots) of InGaAs result. Size distribution measurements from TEM images indicate that these dots are less than 300 angstrom in diameter and remarkably uniform. A phase diagram is constructed, showing the growth conditions under which these strained coherent uniform dots form. Photoluminescence from layers containing these dots is observed and correlated with growth conditions and with structural data obtained from TEM images. We observe that the photoluminescence emitted from the dots and an underlying reference quantum well are nearly equal, indicating a high quantum efficiency for these quantum dots.