Bulk electronic properties of diamond

Abstract

A review of electronic properties of insulating-, boron- and phosphorus-doped diamond is given. The main goal is, to show data in a wider context, to reveal trends and limitations with respect to carrier mobilities, conductivities, p- and n-type doping. Undoped diamond is an insulator with conductivities significantly smaller than 10^-17 Ohmcm at room temperature. Mostly, these insulating films show conductivity activation energies of 1.7 eV, an indication that small amounts of substitutional nitrogen dominates the Fermi-level. The electron and hole mobilities are very high (> 20.000 cm2/Vs at T = 80 K) and are limited by acoustic phonon scattering. By phosphorus and boron doping diamond becomes semiconducting with an n-type donor activation energy (phosphorus) of 600 meV and an acceptor activation energy (boron) of 370 meV. Both dopands are hydrogen-like in nature. Due to the deep donor levels conductivity at room temperature is limited, electronic application will therefore be high-temperature devices. Both, electrons and holes show nearly the same mobilities which is promising for bi-polar applications, however, due to the very different doping levels low temperature devices will be governed by holes with increasing contribution of electrons towards higher temperatures. The effect of temperature on the carrier activation from donors and acceptors, on carrier scattering as well as on transport via hopping is shown in combination with some basic physical models and descriptions. The results confirm the superior electronic properties of diamond which makes it very promising for future electronic applications.