Light-induced Charge Transport Research Articles

Paramagnetic defects in BaTiO3 and their role in light-induced charge transport ? Optical studies

On the basis of a previous identification of paramagnetic defects in nominally undoped as grown BaTiO3 single crystals, we have investigated the changes of the concentrations of these centers and their optical absorptions under illumination with light of varying wavelengths. The most pronounced charge transfers occur by hole ionization of Fe4+ and — to a lesser extent — of Cr5+ and Cr4+. At low temperatures the created holes are trapped in the form of O−-ions next to Al3+ or unknown acceptor defects. Corresponding Fe4+ and O− absorptions have been identified.

Paramagnetic defects in BaTiO3 and their role in light-induced charge transport. I. ESR studies

An overview on paramagnetic defects in BaTiO3 single crystals, used in photorefractive applications, is given. New results concerning cation defects include the investigation of double quantum transitions in isolated F3+, identification of the parameters of Fe4+-V0, analysis of Co2+, the report of Co4+-V0, Jahn-Teller-induced spin-lattice relaxation effects of Pt3+, identification of Rh2+, Rh4+, Ir4+ and Pt5+. In the field of anion defects O- trapped hole centres associated with unknown acceptors and with Al3+ are reported. The role of the identified defects in light-induced charge transport processes is discussed.

Photovoltaic holographic recording in BaTiO3:Fe

Abstract We demonstrate significant contributions of photovoltaic effects to the light-induced charge transport during hologram recording in BaTiO3:Fe. The photovoltaic effects are attributed to the motion of holes.

Applying Kukhtarev's Charge Transport Model to Multiple Quantum-Well Hetero-Nipis

ABSTRACTWe present a model for light-induced charge transport in long-period multiple-quantum-well hetero-nipi structures that is based on Kukhtarev's transport model developed for understanding photorefractive grating formation. We give a simple analytical expression for the steady-state space-charge field in a hetero-nipi under illumination as a function of light intensity.

Photorefractive effects in electrooptic crystals

Abstract The mechanisms responsible for tight-induced refractive index changes are discussed. Special emphasis is paid to the formation of space charge fields and index changes, to Bragg diffraction and selfdiffraction, to photorefractive centers and light-induced charge transport, to various possibilities of nondestructive read-out and to holographic scattering. The ability to tailor certain crystal parameters over wide ranges offers favourable perspectives for future devices.

Light-induced charge transport in LiNbO3:Mg,Cr crystals

Etude des transports de charge induits par la lumiere dans LiNbO 3 :Mg, Cr et LiNbO 3 :Cr par mesures d'absorption optique et holographie. Mise en evidence de l'existence de Cr 4+ et augmentation de la photoconductivite de LiNbO 3 par dopage au magnesium

The light-induced charge transport in LiNbO3:Mg, Fe crystals

Abstract Light-induced charge transport properties of LiNbO3 crystals containing Mg dopants of different concentrations as well as Fe ions in different valence states are studied to obtain quantitative information on the influence of Mg. The experimental results indicate that the photovoltaic effect and the holographic sensitivity are mainly determined by the Fe2+ concentration and depend very weakly on Mg doping or the Li/Nb ratio in the crystals. The photoconductivity, however, increases considerably with increasing Mg concentration thus diminishing the saturation value of light-induced refractive index change.

Influence of Mg doping and composition on the light-induced charge transport in LiNbO3

Light-induced charge transport properties of LiNb03 crystals containing Mg dopants as well as Fe ions in different valence states are studied to obtain quantitative information on the influence of Mg. Also investigated are LiNbO3:Fe crystals with different Li/Nb ratio. The experiments indicate that the photovoltaic effect is determined by the Fe2+ concentration only and depends very weakly on the Li/Nb ratio or Mg doping. The photoconductivity, however, is considerably increased by Mg dopants thus diminishing the light-induced refractive index changes. Lichtinduzierte Ladungstransporteigenschaften werden in LiNbO3-Kristallen mit Mg-Dotierungen und Fe-Ionen in verschiedenen Valenzzustanden untersucht, um quantitative Aussagen uber den Einflus von Mg zu erhalten. Bei den Messungen werden auch LiNbO3:Fe-Kristalle mit unterschiedlichem Li/Nb-Verhaltnis benutzt. Die Experimente zeigen, das der photovoltaische Effekt von der Fe2+-Konzentration bestimmt wird und nur ganz schwach vom Li/Nb-Verhaltnis oder von Mg-Zusatzen abhangt. Dagegen wachst die Photoleitung bei Mg-Dotierung betrachtlich an, und dadurch werden lichtinduzierte Brechungsindexanderungen entsprechend verkleinert.

Light induced charge transport in doped LiNbO3and LiTaO3

Abstract The influence of special dopants on photovoltaic effects and photoconductivity of LiNbO3 and LiTaO3 single crystals is investigated. The measurements clearly indicate that the light induced transport properties can be completely controlled by dopants in suitable valence states. The results yield quantitative correlations thus permitting the derivation of simple models for various contributions to the charge transport.