We report on the preparation of 10 nm lateral size semiconductor structures based on island formation in strained layer growth in molecular beam epitaxy. Red light emitting InP quantum dot injection lasers are presented. They contain densely stacked layers of self-assembled InP quantum dots embedded in a Ga0.51In0.49P wave guide layer. In the second part of this contribution we report on a new atomic layer precise etching technique in MBE, which allows improved interface control for the preparation of semiconductor nanostructures. The etching process involves AsBr3 exposure of a GaAs or AlGaAs surface. Switching between atomic layer precise growth and etching is possible within a few seconds.