PHOTOELECTRONIC PROPERTIES OF YBA2CU3O6

The photocurrent and luminescence properties of thin (1 mum) YBa2Cu3O6 films on sapphire at 77 and 300 K are reported. We demonstrate that t he luminescence mechanism of YBa2Cu3O6 depends considerably on the wav elength of the excitation used. Completely different luminescence resp onses are observed with the 351 and 458 nm lines. A fair agreement, li ke that in semiconductors with band-to-band transitions, is found betw een photocurrent and luminescence excited by the 458 nm line. The infl uence of high electric fields (less-than-or-equal-to 5 780 V cm-1) on the photocurrent and luminescence of YBa2Cu3O6 is investigated for the first time. Similar effects on photon-induced tunneling phenomena (Fr anz-Keldysh effect) are observed. However, we show that the observed e ffects cannot be explained by photon-induced tunneling phenomena only since the influence of an electric field on the band structure of YBa2 Cu3O6 is not only restricted to a bending of bands but modifies the ba nd structure in a more complex manner.