Molecular-based light-activated thyristor

A photoinduced electrical conductivity switching is observed in the molecular conductor of alpha-[bis(ethylenedithio)tetrathiafulvalene](2)I-3 at different temperatures with different irradiation light intensities. The threshold voltage for the differential-negative-resistance effect appearing in the current-voltage characteristic curve decreases and increases, respectively, as the light intensity is increased and as the temperature decreases below the insulator-metal phase transition. The potential application of molecular conductor in bidirectional light-activated thyristor devices is demonstrated. (c) 2007 American Institute of Physics

Single-atomic-layered quantum wells built in wide-gap semiconductors LnCuOCh (Ln=lanthanide, Ch=chalcogen)

LnCuOCh (Ln=lanthanide, Ch=chalcogen) layered oxychalcogenides are wide-gap p-type semiconductors composed of alternately stacked (Ln2O2)2+ oxide layers and (Cu2Ch2)2- chalcogenide layers. Energy band calculations revealed that Cu-Ch hybridized bands only spread in the (Cu2Ch2)2- layers, which suggests that hole carriers in these bands are confined by the potential barriers formed by the (Ln2O2)2+ layers. Stepwise absorption spectra of a series of LnCuOCh experimentally verified that an exciton in the (Cu2Ch2)2- layers shows a two-dimensional behavior. These theoretical and experimental results indicate that LnCuOCh has “natural multiple quantum wells” built into its layered structure

Degenerate p-type conductivity in wide-gap LaCuOS1–xSex (x = 0–1) epitaxial films

Epitaxial films of LaCuOS1–xSex (x = 0–1) solid solution were grown on MgO (001) substrates and their electrical and optical properties were examined. Sharp emission due to room-temperature exciton with binding energy of ~50 meV is observed for all x values. Hall mobility becomes large with an increase in the Se content and it reaches 8.0 cm2V–1s–1 in LaCuOSe, a comparable value to that of p-type GaN:Mg. Doping of Mg2+ ions at La3+ sites enhances a hole concentration up to 2.2×1020 cm–3, while maintaining the Hall mobility as large as 4.0 cm2V–1s–1. Consequently, a degenerate p-type electrical conduction with a conductivity of 140 S cm–1 was achieved

Excitonic blue luminescence from p-LaCuOSe/n-InGaZn5O8 light-emitting diode at room temperature

A hetero p/n junction diode was fabricated by laminating an amorphous n-type InGaZn5O8 layer to a p-type LaCuOSe film epitaxially grown on a MgO (001) substrate. It exhibited a relatively sharp blue electroluminescence (EL) that peaked at ~430 nm at room temperature when a forward bias voltage above 8 V was applied. The wavelength and bandwidth of the EL band agreed well with those of the excitonic photoluminescence band in LaCuOSe, which indicates that the EL band originates from the exciton in LaCuOSe. This experiment strongly suggests that layered compounds, LnCuOCh (Ln=lanthanide, Ch=chalcogen), are promising as the light-emitting layer in optoelectronic devices that operate in the blue–ultraviolet region

Intrinsic excitonic photoluminescence and band-gap engineering of wide-gap p-type oxychalcogenide epitaxial films of LnCuOCh (Ln = La, Pr, and Nd; Ch = S or Se) semiconductor alloys

The optical spectroscopic properties of layered oxychalcogenide semiconductors LnCuOCh (Ln = La, Pr, and Nd; Ch = S or Se) on epitaxial films were thoroughly investigated near the fundamental energy band edges. Free exciton emissions were observed for all the films between 300 and ~30 K. In addition, a sharp emission line, which was attributed to bound excitons, appeared below ~80 K. The free exciton energy showed a nonmonotonic relationship with lattice constant and was dependent on lanthanide and chalcogen ion substitutions. These results imply that the exciton was confined to the (Cu2Ch2)2– layer. Anionic and cationic substitutions tune the emission energy at 300 K from 3.21 to 2.89 eV and provide a way to engineer the electronic structure in light-emitting devices

Third-order optical nonlinearity originating from room-temperature exciton in layered compounds LaCuOS and LaCuOSe

We have studied the third-order optical nonlinearity ((3)) of epitaxial thin films of layered compounds LaCuOS and LaCuOSe at room temperature by a spectrally resolved degenerative four-wave mixing technique with femtosecond time resolution. The (3) values in both films are sharply resonant to optical absorption bands in the ultraviolet (UV) light region due to room-temperature exciton. The peak values are evaluated to be as large as 2–4×10–9 esu with a fast time response of 250–300 fs. These findings indicate that LaCuOS and LaCuOSe are promising materials for emerging optical nonlinear devices that operate in the UV light region compatible for GaN-based lasers

Intrinsic excitonic photoluminescence and band-gap engineering of wide-gap p-type oxychalcogenide epitaxial films of LnCuOCh (Ln = La, Pr, and Nd; Ch = S or Se) semiconductor alloys

The optical spectroscopic properties of layered oxychalcogenide semiconductors LnCuOCh (Ln = La, Pr, and Nd; Ch = S or Se) on epitaxial films were thoroughly investigated near the fundamental energy band edges. Free exciton emissions were observed for all the films between 300 and ~30 K. In addition, a sharp emission line, which was attributed to bound excitons, appeared below ~80 K. The free exciton energy showed a nonmonotonic relationship with lattice constant and was dependent on lanthanide and chalcogen ion substitutions. These results imply that the exciton was confined to the (Cu2Ch2)2– layer. Anionic and cationic substitutions tune the emission energy at 300 K from 3.21 to 2.89 eV and provide a way to engineer the electronic structure in light-emitting devices