The mechanism of low-threshold electron emission from heavily nitrogen-doped diamond was clarified using computer simulation. Possibility of internal field emission at metal-diamond contact was evaluated expecting that the electron injection can explain the low-threshold electron emission. As a result, it was proved that electron injection could be achieved even for a deep donor of 1.7 eV, when donor concentration exceeded 1e20 cm (3). The result was in good agreement with previous experiments. (C) 2008 Elsevier B. V. All rights reserved.