Using photo-lithography and plasma etching processes, we have fabricated high-field-applicable diamond p-i-p structures. Current-voltage (I-V) characteristics of devices thus fabricated, revealed rapid increases in current due to substantial impact excitations, whereas space-charge-limited currents such as I alpha V-2 were observed at sufficiently high electric fields. There were substantial differences in I-V and electroluminescence (EL) properties observed above 1 x 10(6) V/cm between N-contained high-temperature/high-pressure-synthesized diamond and undoped chemical-vapor-deposited (CVD) diamond, indicating that these characteristics strongly depend on the Fermi level of the diamond i layer employed. Cathodoluminescence data were also compared with the EL data. (c) 2004 Published by Elsevier B.V.