Electronic states of phosphorus in diamond

A set of rt-type diamond thin films was investigated by infra-red absorption spectroscopy. The films were grown by CVD on {111} synthetic diamond, and phosphorus-doped using [P]/[C] = 100-5000 ppm of phosphine in the gas phase during growth. The phosphorus concentration in the films ranged from around 5 x 10(17) cm(-3) to 2 x 10(19) cm(-3). A continuum of absorption, attributed to the photoionisation of neutral phosphorus, is observed together with two peaks at 523 and 562 meV attributed to electronic transitions from the ground level of phosphorus to its first and second excited states. The energy difference between these two peaks is in agreement with the effective mass approximation applied for the rt-type diamond, suggesting that phosphorus behaves like a shallow level centre. Assuming that phosphorus is a perfect shallow level, the optical ionisation energy of 600 meV (+/- 20 meV) is deduced, consistent with the thermal activation energy. (C) 2000 Elsevier Science S.A. All rights reserved.