Chemically assisted ion beam etching (CAIBE) of InP-based materials has been newly developed with BCl3/Ar in comparison to Cl2/Ar and IBr3/Ar. Using halogen gases and an argon ion beam at 400 V a very good surface morphology was obtained at a low substrate temperature of -5 °C in any case; with BCl3/Ar a surface roughness of 0.2 nm was observed. The etch rates were in the range of 40–75 nm/min depending on the reactive gas. Mixing the reactive gases or tilting the substrate with respect to the impinging ion beam allowed us an excellent control of the etched sidewall slope. By mixing BCl3 and IBr3 we were able to tune the sidewall slopes between 15° (measured to the surface normal) for pure BCl3 and 38° for the pure IBr3, respectively. Tilting the substrate allowed us to adjust the slope angle between 0° and 60°. In addition we have analyzed the etched surfaces by energy dispersive x-ray measurements. The low temperature processes yielded stoichiometric InP surfaces, etching at higher substrate temperatures results nonstoichiometric surfaces. These low temperature halogen CAIBE processes were successfully applied for the fabrication of gratings, ridge waveguides and facets for long wavelength (InGa)(AsP) and (AlInGa)(AsP) laser diodes. In this article we present ridge waveguide (InGa)(AsP)/InP lasers (1.55 μm) with direct CW modulation bandwidths of 9.5 GHz. © 1998 American Vacuum Society.