Performance enhancement of diamond p+–i–n+ diodes employing electron injection through heavily nitrogen–doped layers

Nitrogen (N) is an attractive dopant candidate for n–type diamond because it can be incorporated at higher concentrations than phosphorus, yet the practical use of N–doped n–type diamond has been hindered by poor room–temperature conductivity and large resistive losses. To improve the conductivity in diamond pin diodes with heavily N–doped n + –type layer, we fabricated two device structures with intentionally thinned intrinsic and n + –type layers: a p + –p–i–n + diode for excitonic electroluminescence (EL) and a p + –i–n + diode for high–current evaluation. The heavily N–doped n + –type layer was precisely controlled to ∼100 nm, enhancing the electric field at the metal / n + –type layer interface to facilitate effective reduction of the contact resistance. Excitonic deep–ultraviolet EL measurements confirmed electron injection and bipolar operation, exhibiting free–exciton–related emission peaks at 235 and 242 nm and a turn–on behavior around 3 V. The optimized p + –i–n + diode showed forward J – V characteristics comparable to pin diodes with phosphorus–doped n + –type layer and achieved an approximately five–orders–of–magnitude increase in forward current density compared with previously reported pin diodes with N–doped layer. Differential–resistance analysis revealed that the effective n–type contact resistance decreased to ∼10 −1 Ω·cm 2 at ∼6 V, highlighting N as a practical dopant for forming an electron–injection layer in diamond and motivating further optimization toward higher–current bipolar operation.