PHOTOCONDUCTIVITY OF UNDOPED, NITROGEN-DOPED AND BORON-DOPED CVD-DIAMOND AND SYNTHETIC DIAMOND

Nitrogen-doped CVD- and synthetic type IIa and Ib diamonds were invest igated by the constant photocurrent method (CPM). Nominally undoped CV D-films containing nitrogen show broad absorption bands with threshold energies at 1, 2.3, 3 and 4.2 eV. The typical nitrogen donor absorpti on band with a threshold at 1.7 eV is partially masked by the 1 eV ban d in CVD-films. The absorption bands are too broad to be described by simple theories based on photoionization of single unbroadened impurit y 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 oscillat ory photoconductivity minima due to fast capture of holes by the excit ed states of boron accepters. In CVD-films with boron concentrations a round 10(19) cm(-3), the oscillation pattern inverts at low temperatur es and sharp minima were found in the spectrum. (C) 1998 Elsevier Scie nce S.A.