Single-level interface states inn-type GaAs, which were incorporated by planar doping of deep-level defects, are investigated. Discrete electronic traps are directly identified as interface states by admittance-bias spectra. It is experimentally demonstrated that the characteristic response time is determined by both the emission and the capture rate when interface states are investigated by admittance spectroscopy. The transition between capture- and emission-controlled admittance spectra is observed. ©1997 American Institute of Physics.