The As doping mechanism in (100) CdTe layers grown on ( 100) GaAs by atmosphericpressure metalorganic vapor phase epitaxy was studied. Triethylarsine (TEAS) was used as a dopant source. The source materials used were dimethylcadmium (DMCd) and diethyltelluride (DETe) . The As incorporation was enhanced by decreasing the DETe flow rate under a fixed DMCd flow condition, and by lowering the growth temperature. Assuming 100% activation of As, the As incorporation efficiency was estimated to be about 0.1%. The As incorporation was dominated by the sticking rate of the As species onto the Cd species. The hole concentration was controlled from 2x 1015 to 3 x lOi cm -3 in proportion to the TEAS flow rate below 1 x lo-' mol/min. Those doped layers showed hole mobilities as high as 75 cm2/V s. Low-temperature photoluminescence (PL) studies revealed that a neutral-acceptor bound-exciton at 1.5901 eV is due to a substitutional As acceptor on the Te site. The As ionization energy was about 90 meV from the PL and electrical measurements.

CdS films were cathodically electrodeposited from acidic solutions (pH=2.5) containing CdSO4 and Na2S2O3. Raman scattering of these films was measured using the 514.5 nm line of an Ar ion laser as the light source. The longitudinal-optical (LO) phonon peak of CdS was observed between 300–310 cm-1. The full width at half-maximum (FWHM) of the peak was a large value of 18.2 cm-1 for as-deposited films, but decreased to 12.7 cm-1 after the films were annealed at 500° C. These results are consistent with those of other structural and optical characterizations, and thus the Raman spectroscopy was found to be useful for the characterization of the electrodeposited CdS films.

SYNOPSIS Responses of Paramecium bursaria to light intensity changes were investigated. The resting paramecia show a direction changing response (photophobic response) to a sudden decrease of light intensity, whereas no response was shown to an increase in intensity. The critical intensity decrease dIc necessary to show the response was measured at various values of initial light intensity, and the ratio dIc/I was found to be equal to ∼0.15. The swimming paramecia show different behavior depending on their swimming direction in the spatial gradient of light intensity. Paramecia show direction change more frequently when they are swimming down the gradient than in the opposite direction. This difference in the rate of direction changing is 13–17%. These results may offer an explanation for the mechanism of photoaccumulation.

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