A large range of boron doping with low compensation ratio for homoepitaxial diamond films

A large range ([B] from 5 x 10(16) to 8 x 10(20) cm(-3)) of boron concentration has been obtained for homoepitaxial diamond films. From the variation of the conductivity versus temperature between 300 and 1000 K, a simpler method is used to derive the activation energy(ies) E-a and the compensation ratio than from the variation of the hole concentration and mobility with temperature. For [B] < 2 x 10(17) cm(-3), a saturation of the conductivity is observed between 680 and 1000 K, E-a = E-i (ionisation energy of the boron), and compensation ratio around 10% is deduced. Then, up to 10(19) cm(-3), an additional E-a = E-i/2 = 185 meV is observed between 500 and 1000 K, with compensation ratio <10%. At higher [B], an additional nearest neighbour hopping contribution to the conduction is obtained from the formation of the boron impurity band. It dominates and gives metallic conductivity when [B] = 3 x 10(20) cm(-3). (C) 1999 Elsevier Science Ltd. All rights reserved.