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In this work we have measured the lateral spontaneous emission profile for the lasers, using scanning near-field optical microscopy (SNOM). Since the near-field of the spontaneous emission maps the lateral carrier distribution in the active region, this measurement provides a way to directly measure the lateral diffusion. The obtained profile therefore represents the optical mode which is well confined beneath the ridge. Carriers that diffuse outside the ridge can hence not contribute to optical gain and are therefore associated with a leakage current.