Bipolar n(+)pp(+) diodes fabricated by nitrogen implantation and passivated with a deposited oxide have been characterized. Current-voltage measurements in a large temperature range have been analyzed. We also used the optical beam induced current method to represent the depleted zone at the surface around a reverse-biased device. We show that phenomena as the diameter-dependent current for low reverse and forward biases, the specific value for the energy activation of current under low bias equal to 0.65 eV, the reverse current-voltage characteristics evolution with time, or the anomalous spread of the depleted layer around a reverse-biased diode can be correlated with the presence of the deposited oxide as a passivation layer. A study of the current-time characteristic, obtained for a set reverse bias, is used to prove the presence of charges in the oxide and interface states responsible for an eventual inversion channel along the mesa. (C) 1998 American Institute of Physics.