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Zinc oxide (ZnO) single crystals were grown by the hydrothermal method using a platinum inner container. The 2 inch ZnO wafers obtained from these bulk crystals possess an extremely high crystallinity and purity. The electrical resistivity is highly uniform over the entire wafer area. After annealing, the step-and-terrace structure was observed on the surface of the wafer. The etch pit density was decreased to less than 80 cm −2 . These results suggest that these 2 inch ZnO wafers are suitable for wide band gap device applications.

Intestinal stem cells (ISCs) are required for maintenance of the proper cell composition in the adult intestine. To ensure permanent recruitment of newly differentiated cells, the ISC undergoes asymmetric cell division that generates an ISC itself and a progenitor cell. In the Drosophila midgut, cell fate for the absorptive cell is determined by Notch (N) signal in the progenitor cells that receive a ligand Delta (Dl) produced by the ISCs. Although most of the ISCs and progenitor cells are distantly located, they should retain their attachment when N is activated because the Dl–N interaction requires cell adhesion. Furthermore, N cannot be activated before completion of cell division. Thus, the moment after cell division and before cell separation should be prolonged for certain N activation, although the mechanism for this remains unclear. Here, we demonstrate that E‐cadherin (E‐cad) is required for stable attachment between the two cells. When E‐cad does not function, N is not activated and cell differentiation is attenuated. We also show that the ISC tumor by N inactivation is assisted by a defect in E‐cad down‐regulation. These findings reveal one of the normal N functions used to inhibit tumorigenesis through lowering of E‐cad for proper midgut cell turnover.

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Photoconductivity of ZnO single crystals grown by a hydrothermal method for ultraviolet light was measured. The ZnO single crystals have photo response in a range of wavelengths shorter than 380 nm. Ofaces of ZnO single crystals of the c-plane showed higher photocurrents and wider spectral response than did Zn-faces. It is thought that band bending at the surface regions of ZnO crystals is large at the O-face but small at the Zn-face, because the surface state density for electron capture at the O-face was higher than that of the Zn-face and, therefore, carriers generated at the surface region by UV light were effectively separated at the O-face region before their recombination. The difference between photoresponces of the O-face and the Zn-face is also useful for determining the polarity of a ZnO crystal.