Boron–hydrogen complexes in diamond and their vibrational properties

Abstract

Diamond is a promising candidate material for high power, high temperature and high frequency electronics. Boron is well known as a shallow acceptor in diamond. Recently diamond has been successfully shallow n-type doped by introducing an excess of deuterium in high quality B doped diamond, enabling a reversible p-type to n-type conversion of B doped diamond. However, the nature of this new shallow donor has been the subject of debate. We calculate the properties of boron and its complexes with hydrogen in diamond, using accurate ab initio plane wave Density Functional Theory (DFT) methods, and show that BH 2 centres are stable with small binding energies of 0.23 to 0.71 eV, consistent with experimentally observed dissociation of the new donor at relatively low temperatures of 200 °C, and explain the two-step deuteration process in high quality boron doped diamond. Our ab initio Plane Wave periodic supercell DFT theory calculations confirm the existence of a BH induced level at E c – 0.96 eV. We further show that the BH 2 centre possesses a very deep donor level, excluding the possibility of BH 2 doping the BH impurity band previously suggested. To facilitate experimental determination of the nature of the new shallow donor, we determine the Local Vibrational Modes of BH and BH 2 centres in different charge states, together with isotope shifts, which may be compared with experiment, towards establishing the nature of the new donor.