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

: Rohrer, E.; Nebel, C.E.; Stutzmann, M.; Floter, A.; Zachai, R.; Jiang, X.; Klages, C.-P.


Diamond and Related Materials 7 (1998), No.6, pp.879-883
ISSN: 0925-9635
Journal Article
Fraunhofer IST ()
photoconductivity; CVD- and synthetic diamond; boron; nitrogen

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 eV band in CVD-films. The absorption bands are too broad to be described by simle 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 accepters. In CVD-films with boron concentrations around 10(19) cm(-3), the oscillation pattern inverts at low temperatures and sharp minima were found in the spectrum.