Unveiling n-type surface charge transfer doping of diamond via MgO nanocubes: A first-principles study

The application of ultra-wide bandgap diamond in semiconductor technologies relies on precise control of carrier type and density. However, conventional n-type bulk doping remains difficult due to diamond's strong covalent bonds and deep donor levels. Surface charge transfer doping (SCTD) offers a promising alternative by exploiting energy-level differences between dopants and the semiconductor, avoiding activation energy. While organic molecules and alkali metals as surface dopants can achieve n-type doping on oxygen-terminated diamond (100) surfaces, their thermal and chemical instabilities hinder long-term device stability. In this work, we use first-principles calculations to investigate n-type SCTD on oxygen-terminated diamond (100) surfaces using MgO nanocubes as stable electron donors. MgO enables efficient electron transfer, shifting the Fermi level—the highest occupied electronic state at 0 K—into the conduction band, thereby confirming successful n-type doping. The maximum areal electron density reaches 1.98 × 10¹³ cm⁻²—comparable to organic doping (~2.60 × 10¹³ cm⁻²) and about one order lower than alkali metal doping (~2.50 × 10¹⁴ cm⁻²)—with significantly improved stability. The doping performance is tunable via the thickness of the diamond and MgO layers, as well as nanocube size and density. Additionally, MgO enhances the infrared response of diamond by introducing a 0.4 eV absorption peak with an absorption coefficient of 7 × 10³ cm⁻¹. These results offer atomic-level insights into stable, tunable n-type doping and point to MgO-modified diamond surfaces as promising candidates for mid-infrared optoelectronic applications.