Use of atomic force microscopy for analysis of high performance InGaAsP/InP semiconductor lasers with dry-etched facets

We report on the use of an atomic force microscope (AFM) to directly measure the quality of InGaAsP/InP laser facets formed by a CH4:H2:Ar reactive ion etching process. From the AFM data, we obtain values for rms surface roughness and transverse angular tilt that have previously only been estimated through laser operating characteristics or inferred from scanning electron microscope analysis. The etched facet reflectivity, calculated from device slope efficiency data and far-field beam profiles, is in excellent agreement with AFM measurements. We show methane-based dry etching can achieve a rms facet roughness of 22 nm. This value surpasses the generally accepted roughness parameter of λ/10 and is competitive with the best chlorine-based facet etching to date. We also report a transverse angular facet tilt of 2°, which we believe to be the most vertical, CH4-based facet etch reported to date. The output performance of these devices is nearly identical to cleaved devices.