Hybrid diamond materials (HBDs) were synthesized using a two-step bias enhanced nucleation and growth process (BEN-BEG). The secondary BEG process efficiently altered the granular structure of the underlying ultrananocrystalline diamond (UNCD) films, rather than growing a nanocrystalline diamond (NCD) film on the top of the UNCD layer. Nanographite clusters were formed when the coalescence of ultra-small diamond grains was induced due to the secondary BEG process that enhanced the transport efficiency of electrons and thus improved the electron field emission (EFE) properties of the HBD films. However, the depth of interaction increased with the magnitude of the bias voltage applied in the secondary BEG process. Therefore, large enough bias voltage (− 300 V) is required in the secondary BEG process to convert the whole thickness of UNCD films into HBD ones. The EFE properties of HBD− 300 V films can be turned on at a low field of E0 = 3.36 V/μm and attained a high EFE current density of Je = 4.57 mA/cm2 at an applied field of 6.4 V/μm. The synthesis of HBD films with high conductivity and excellent EFE behavior enables them to be better EFE emitters with improved performance in flat panel display applications.