Optical and electrical characteristics of AlGaAs lasers with separate confinement heterostructures are modeled by using Synopsys's Sentaurus TCAD, and open source software. We propose a modified exponential I − V dependence to describe electrical properties. A simple analytical, phenomenological model is found to describe optical efficiency, η, with a high accuracy, by using two parameters only. A link is shown between differential electrical resistivity r = dU/dI just above the lasing offset voltage, and the functional η(U ) dependence.