Design of shallow donor levels in diamond by isovalent-donor coupling.

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 N + 4Si 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 N + 4Si complex is also large enough to insure its stability.