Boron–oxygen complex yields n-type surface layer in semiconducting diamond

Significance

Diamond is a uniquely attractive wide-bandgap semiconductor for future electronic devices where its remarkable physical properties may enable switches, transistors, and diodes for extreme applications. Whereas p-type semiconducting diamond is well developed with boron doping, the synthesis of n-type diamond, required to complete purely diamond-based electronics, has been a great challenge in materials science. We report the creation of n-type diamond via a new type of defect complexes of boron and oxygen that can be tuned by controlling the experimental parameters for diamond crystallization, leading to a shallow donor state with high carrier concentration that is several orders of magnitude higher than achieved by sulfur or phosphorus doping. The results provide a new strategy for producing n-type diamond-based devices.

Abstract

Diamond is a wide-bandgap semiconductor possessing exceptional physical and chemical properties with the potential to miniaturize high-power electronics. Whereas boron-doped diamond (BDD) is a well-known p-type semiconductor, fabrication of practical diamond-based electronic devices awaits development of an effective n-type dopant with satisfactory electrical properties. Here we report the synthesis of n-type diamond, containing boron (B) and oxygen (O) complex defects. We obtain high carrier concentration (∼0.778 × 10 ²¹ cm ⁻³) several orders of magnitude greater than previously obtained with sulfur or phosphorous, accompanied by high electrical conductivity. In high-pressure high-temperature (HPHT) boron-doped diamond single crystal we formed a boron-rich layer ∼1–1.5 μm thick in the {111} surface containing up to 1.4 atomic % B. We show that under certain HPHT conditions the boron dopants combine with oxygen defects to form B–O complexes that can be tuned by controlling the experimental parameters for diamond crystallization, thus giving rise to n-type conduction. First-principles calculations indicate that B ₃O and B ₄O complexes with low formation energies exhibit shallow donor levels, elucidating the mechanism of the n-type semiconducting behavior.