Photoconductivity of undoped, nitrogen-and boron-doped CVD-and synthetic diamond

摘要

Nitrogen-doped CVD- and synthetic type IIa and Ib diamonds were investigated by the constantphotocurrent method (CPM). Nominally undoped CVD-films containing nitrogen show broadabsorption bands with threshold energies at 1, 2.3, 3 and 4.2eV. The typical nitrogen donorabsorption band with a threshold at 1.7 eV is partially masked by the 1 eV band in CVD-films. Theabsorption bands are too broad to be described by simple theories based on photoionization of singleunbroadened impurity levels. Boron-doped CVD- and type IIb synthetic diamond was studied byphotoconductivity and photothermal ionization in the near infra-red. The large electron-phononcoupling in diamond gives rise to oscillatory photoconductivity minima due to fast capture of holes bythe excited states of boron acceptors. In CVD-films with boron concentrations around 10{sup}19cm{sup}-3, the oscillation pattern inverts at low temperatures and sharp minima were found in thespectrum.