The demonstration of diamond devices has substantiated the superior capability of diamond in high power electronics that relied on the preparation of p-type and n-type diamond through boron and phosphorus doping, respectively, and the growth of high purity intrinsic diamond. We present an approach for electrical contacts to homoepitaxial, phosphorus doped, n-type, diamond that utilizes an interfacial layer of highly nitrogen doped, nanostructured carbon grown by plasma enhanced CVD (PECVD). This contact strategy was utilized in a pin diamond diode for electron source applications. The pin-nano-carbon structure was prepared on HPHT type IIb (111) oriented substrates with intrinsic, n-type, and nano-carbon layer grown in dedicated PECVD systems. The nanostructured nitrogen doped carbon layer was synthesized under argon addition to promote re-nucleation. Diodes from this pin-nano-carbon structure were prepared by lithography and mesa-etched devices contacted by Ti/Pt/Au metallurgy. Final processing in a hydrogen plasma established negative electron affinity properties for electron emission. Electrical characterization of the diodes commenced in vacuum after annealing at ~600 °C for 15 min and observation of exciton light emission indicated bipolar transport. At a forward bias of 14 V a current of 0.1A was measured and at 17 V its increase to 0.5A corresponded to a current density >1500 A/cm2. Compared to conventional pin diodes, the introduction of the nano-carbon layer enhanced the diode and electron emission current by more than an order of magnitude. This was attributed to the reduced contact resistivity of 5.5 × 10−3 Ω cm2 at room temperature. Light emission and diode operation at temperatures >750 °C indicated superior stability of the electrical contact. The n-type layer was characterized by SIMS indicating a phosphorus incorporation of ~2 × 1019cm-3 and for the nano-carbon layer a nitrogen incorporation of ~5 × 1020cm−3. Addressing contact limitations to n-type diamond through the growth of moderately phosphorus doped epilayers followed by highly nitrogen doped nano-carbon layers could provide a preferred approach for electronic devices that could also be extended to (100) surfaces.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Mechanical Engineering
- Materials Chemistry
- Electrical and Electronic Engineering