Electronic properties of c-BN/diamond heterostructures for high-frequency high-power applications

Using first principles calculations, this work investigates the suitability of diamond/c-BN heterojunctions for high frequency, high power device applications. The key quantities of band offsets and interface charge polarization are examined for different crystallographic orientations [(110), (111), or (100)], bond terminations (CB or CN), and substrates (diamond or c-BN). The results indicate that both the (111) and (100) structures with polar interfaces are likely to be a type-I alignment with the diamond conduction and valence band extrema nested within the c-BN bandgap, whereas the non-polar (110) counterpart may form type II as the valence band of c-BN is shifted down substantially lower. The valence band offsets are estimated to be around 0.2–0.55 eV and 1.2–1.3 eV for types I and II, respectively, with only a modest dependence on the order of layer stacking and bond termination. The (111) and (100) structures also show net charge polarization in a narrow region at the interface. The electron-deficient and electron-rich nature of the CB and CN bonding are found to induce charge redistribution leading to an essentially 2D sheet of negative and positive polarization, respectively, with a density on the order of 1012−1013q/cm2 (q=1.6×10−19 C). With the predicted band alignments suitable for carrier confinement as well as the possibility of the modulation and polarization doping, the diamond/c-BN heterostructures are a promising candidate for high-performance electronic devices with a highly conductive 2D channel. Both p-type and n-type devices appear possible with a judicious choice of the heterojunction configuration.