Depth profile analysis by high-resolution secondary ion mass spectrometry (SIMS) can accurately determine C and Si concentrations within monolithic reflectors of vertical cavity surface-emitting lasers (VCSELs). These SIMS depth profiles are quantified to atomic concentrations using relative sensitivity factors and calibration standards, and are correlated to the laser characteristics. We compare the light output versus current and voltage of a conventional oxide-confined VCSEL with a self-pulsating VCSEL. We show that SIMS depth profiling of VCSELs can be useful as a diagnostic method for VCSEL epitaxial wafers, and that the doping level of oxide aperture layers can dramatically impact the device performance. (C) 2004 American Vacuum Society.