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

Abstract

Abstract Nitrogen-doped CVD- and synthetic type IIa and Ib diamonds were investigated by the constant photocurrent method (CPM). Nominally undoped CVD-films containing nitrogen show broad absorption bands with threshold energies at 1, 2.3, 3 and 4.2 eV. The typical nitrogen donor absorption band with a threshold at 1.7 eV is partially masked by the 1 eV band in CVD-films. The absorption bands are too broad to be described by simple theories based on photoionization of single unbroadened impurity levels. Boron-doped CVD- and type IIb synthetic diamond was studied by photoconductivity and photothermal ionization in the near infra-red. The large electron-phonon coupling in diamond gives rise to oscillatory photoconductivity minima due to fast capture of holes by the excited states of boron acceptors. In CVD-films with boron concentrations around 1019 cm−3, the oscillation pattern inverts at low temperatures and sharp minima were found in the spectrum.