We report on photoluminescence studies on a high mobility 2-dimensional electron gas (2DEG) in a heterostructure. We observe an intense recombination line which originates from the 2DEG. By applying a semi-transparent Schottky gate we prove that the line originates form the 2DEG. The intensity can be changed by varying the electron density between 0 and 7·1011 cm-2. We observe a blue shift of the recombination line induced by photocarriers. The blue shift is about 10 meV for an excitation density of 1 W/cm2. It is related to electrostatic effects due to built-up of photogenerated carriers causing bandstructure modifications. In particular, a shallow confinement potential for the holes occurs. From the strong temperature dependence of the luminescence around 10 K, the depth is estimated to be 1.5 meV.