P and N compensation in diamond molecular orbital theory

Cluster models and the atom superposition and electron delocalization molecular orbital theory calculations lead to an explanation for the ability of nitrogen to cause phosphorous incorporation in low pressure grown diamond films as observed recently by Cao and coworkers.(5-7) The theory shows that substitutional N compensates substitutional P, creating stable P+-N- disubstitutional pairs. These ionized systems are calculated to be deep donors, which explains the absence of measurable electrical conductivity or phosphorous induced luminescence. The possibility of creating donor P defects by the annealing reaction P-N+N-->P+N-N is discussed. The issues of atom site and electronegativity and their influence on donor capability are addressed. It is shown that the difference between substitutional P, a shallow donor, and substitutional N, a deep donor, is predominantly due to the larger size of P; its lower electronegativity makes a relatively small contribution. (C) 1997 American Institute of Physics.