The electrostatic potential profile across the p-n junction of an InGaAs light-emitting diode with linearly graded AlGaAs triangular barriers has been measured using off-axis electron holography. Simulations of the junction profile show small discrepancies with experimental measurements in the region of the p-and n-doped AlGaAs barriers, which are located away from the InGaAs quantum wells. Revised simulations reproduce the measurements reasonably when a carrier-trap density of 6x10(16) cm(-3) in the AlGaAs barriers is subtracted from the dopant concentrations. The presence of oxygen impurities is considered as the most likely reason for the reduction in doping efficiency.