The sensitization of natural semiconducting anatase crystals from two different locations was investigated using a ruthenium-based dye ͑cis-di͑thiocyanato͒-bis͑2,2Ј-bipyridyl-4,4Ј-dicarboxylate͒ruthenium͑II͒, also known as N3͒. A maximum incident-photon to sensitized photocurrent conversion efficiency of 3.2 ϫ 10 Ϫ4 was measured. The crystal face dependence of the sensitization efficiency was also investigated as well as the adsorption kinetics for N3. The efficiency of sensitization of the ͑101͒ face was approximately one order of magnitude higher than for the ͑001͒ face. Various surface binding geometries for N3 on the two anatase crystal surfaces are discussed. Sensitization yields that varied by a factor of four were also observed on ͑101͒ faces depending on the identity of the crystal. Examination of the morphology of the crystal surfaces with atomic force microscopy and scanning electron microscopy indicated that differences in sensitization efficiency on different faces and crystals were not solely the result of differences in microscopic surface areas. The rise time for sensitized photocurrents decreased with higher light intensities and higher N3 coverages suggesting that trap states, associated with trapping and detrapping of injected electrons, can be saturated. The comparison of the sensitization behavior between anatase single crystals ͑natural and synthetic͒ and nanocrystalline anatase films revealed that the absorbed photon-to-current efficiency of the nanocrystalline films is approximately three to seven times greater than on single crystals.

No abstract

Tin disulfide is a layered semiconductor, crystallizing in the cadmium iodide structure, with a band gap of 2.2 eV. The layered structure makes it useful for many experiments where a semiconductor with a reproducible renewable surface is needed. The easy cleavage of the surface exposes a clean atomically flat surface for use as a substrate for the deposition of solid-state materials or molecules or scanning probe microscopy experiments. Its semiconducting properties are also useful for photoelectrochemical dye sensitization studies. We report the crystal growth of this material by a Bridgman method with control of the dopant identity and level to obtain useful n-type semiconducting properties. Doping levels measured with both Hall effect and Mott Schottky analysis were well correlated. The electron mobility and hole diffusion lengths were also measured for the various doped crystals using solid-state and photoelectrochemical techniques.

No abstract

The surface morphology of (100) n-InP samples photoelectrochemically etched in homogeneous white light was studied. The photoelectrochemical etches were strongly anisotropic and resulted in the production of microstructures, the size and shape of which depended on the charge density and applied potential, respectively _At more positive etching potentials V-grooves aligned along the [011] axis were formed, delineated by the ( 111) and ( 111) indium etch stop planes, whereas etching at more negative potentials resulted in the formation of rectangular shaped pits oriented along the [0111 axis. These pits were composed of large ( 111) and ( 111) indium etch stop planes and a more complex stepped structure which was analyzed in detail. We explain the relationship between the etching potential and the resulting structures by calculating the distribution of photogenerated minority carriers in the region below the surface of the semiconductor. InfroductionThe morphology of etched semiconductor surfaces is an area of direct concern to the microelectronics industry.' Isotropic etching of semiconductors is used to produce polished surfaces while maintaining the identity of the initial crystalline plane. Anisotropic etching, on the other hand, can be used to expose crystalline planes other than the initial surface. Anisotropic etching through a mask can result in the formation of a V-groove profile, such as that employed in the fabrication of V-groove field effect tran-sistors2 or multijunction solar cells.3 However, if an entire crystalline surface is submitted to anisotropic etching it can develop a strong texture.4'5 This texture can be used to substitute antireflective coatings on photovoltaic materials such as Si, GaAs, and InP, thereby increasing light