Using the first-principles pseudopotential method, we have studied simultaneous isovalent and $n$-type doping in diamond. We show that Si induces fully occupied isovalent levels near the valence band maximum. The Si levels interact with N donor levels, making them much shallower. The donor transition energy level of the $\mathrm{N}+4\mathrm{S}\mathrm{i}$ defect complexes is found to be 0.09 eV below the conduction band minimum, which is the shallowest level found thus far for this system. The binding energy of the $\mathrm{N}+4\mathrm{S}\mathrm{i}$ complex is also large enough to insure its stability.

• Received 17 June 2003

DOI:https://doi.org/10.1103/PhysRevLett.91.126406