Broad‐area InGaAsP/InP lasers emitting at 1.55 &mgr;m have been fabricated from material grown by liquid phase epitaxy. The effects of different levels of zinc doping of the antimeltback layer combined with light doping (≤5×1017cm−3) of the InP cladding layers have been studied. Threshold current densities of 2.1–2.3 kA cm−2are found under a range of zinc‐doping levels. The quantum efficiencies are highest, approximately 19% per facet, when the antimeltback layer is undoped. With zinc doping, the quantum efficiencies drop by a factor of 2–3. Photoelectrochemical etching has been used to reveal thep‐njunction. The etching shows that the zinc doping yields an increase in the small scale variations in the placement and abruptness of thep‐njunction.