The efficiency and operating range of a photonic crystal laser are improved by passivating the In-GaAs quantum well gain medium and GaAs membrane using a (NH4)S treatment. The passivated laser shows a fourfold reduction in nonradiative surface recombination rate, resulting in a fourfold reduction in lasing threshold. A three-level carrier dynamics model explains the results and shows that typical parameters of such lasers lead to a lasing threshold as much determined by surface recombination as by the overall impact of the cavity quality factor. Surface passivation therefore appears crucial in operating such lasers under practical conditions. (c) 2007 American Institute of Physics.