Potential imaging of operating light-emitting devices using Kelvin force microscopy

We report on the measurements of two-dimensional potential distribution wit h nanometer spatial resolution of operating light-emitting diodes. By measu ring the contact potential difference between an atomic force microscope ti p and the cleaved surface of the light emitting diode, we were able to meas ure the device potential distribution under different applied external bias . It is shown that the junction built-in voltage at the surface decreases w ith increasing applied forward bias up to flatband conditions, and then inv erted. It is found that the potential distribution is governed by self-abso rption of the sub-band-gap diode emission. (C) 1999 American Institute of P hysics. [S0003-6951(99)01320-0].