Low temperature excitation spectrum of phosphorus in diamond

A set of n-type diamond thin films was investigated by infrared absorption spectroscopy from 4 K to 300 K. The films were grown by CVD on {111} synthetic diamond, and phosphorus-doped using from [P]/[C] = 100 to 1000 ppm of phosphine in the gas phase during growth. The phosphorus concentration in the films ranges from approximately 5 x 10(17) cm(-3) to 5 X 10(18) cm(-3). At low temperature new absorption peaks were observed for the first time, and attributed to the 3P(+/-) excited state: of phosphorus and phonon-assisted electronic transitions. The energy of this new excited state is in accordance with the effective mass approximation, confirming the shallow level behaviour of phosphorus in diamond. Furthermore, this good agreement allowed us to propose accurate values of the electron effective masses (m(perpendicular to) and m(parallel to)) and of the optical ionisation energy. A correlation between the electron mobility and the broadening of the phosphorus excited states was observed among the samples, giving new insights on the processes reducing the electron mobility. (C) 2001 Elsevier Science B.V. All rights reserved.