High resolution cathodoluminescence microscopy (CL) under a magnetic field is proposed and used to study the interface structure of GaAs-AlGaAs single quantum wells. This principle called, Lorentz-force Carrier-confinement (LC), successfully improves the resolution by up to a few thousand Angstrom. Periodic light and dark stripe patterns are observed in LC-CL monochromatic images of the single quantum wells on the intentionally-tilted substrates. It is shown that the stripes represent stair-like stepped interfaces and that the observed terraces are extended and the steps are clustered. Based on the results, a new interface structure model is proposed, that takes the tilting into account.