Kazuya Kogure

Tilt Compensation Method of Two-Beam Angle Multiplexing Holographic Memory

In a two-beam angle multiplexing holographic memory, there is a problem that the tilt margin is small. Therefore, we propose a radial tilt compensation method (radial tilt is a tilt in the vertical direction to a surface that is made by reference and signal beams). When the radial tilt occurred during the reading, we brought the relative angles of interference fringes and the reference beam near the state at the time of recording. Concretely speaking, we shifted the disc to the circumferential direction slightly to obtain the optimum signal-to-noise ratio (SNR) and then recovered the hologram. In our experiments, we recorded 1 hologram (no multiplexing) and 51 multiplexing holograms, and recovered them using this compensation method. As a result, we confirmed that our method improved the tilt margin markedly in both cases. This compensation method is thus effective for interchangeability without the need for an additional mechanism and making for smaller drives.

Crystalline Silicon Solar Cells with Two Different Metals

We propose crystalline silicon solar cells with Al and Au metals. P-type substrates were coated with 100-nm-thick thermally grown SiO2 layers. The top SiO2 layer was thinned to about 1.5 nm. Stripes of Al and Au were formed with a gap of 0.29 mm on the top surface in order to cause an internal built-in potential in silicon because of the difference between their work functions. Solar cell characteristics were observed by halogen lamp illumination at 21.7 mW/cm2. The short-circuit current density, open-circuit voltage, and fill factor were 5.8 mA/cm2, 0.49 V, and 0.57. The conversion efficiency was 7.5%. Photo-induced holes and electrons flowed into Au and Al electrodes, respectively, by the tunneling effect.

Minority Carrier Lifetime Measurements by Photoinduced Carrier Microwave Absorption Method

We propose a measurement system for photoinduced minority carrier absorption of 9.35 GHz microwaves using periodically pulsed light illumination at 620 nm. The ratio of average carrier density when light illumination is ON to that when light illumination is OFF, P, was theoretically analyzed for different light pulse widths. The analysis of P resulted in a formula giving the minority carrier lifetime τeff of silicon under continuous light illumination. τeff for holes was experimentally determined using the formula, and its spatial distribution was obtained to be from 1.0 ×10-3 to 1.28 ×10-3 s for n-type silicon substrates with a thickness of 520 µm coated with 100-nm-thick thermally grown SiO2 layers. We also demonstrated that τeff depended on the means of light illumination for a defective sample. Two different τeff values were obtained, 7 ×10-5 and 1.73 ×10-4 s, in the cases of light illumination to the top surface and rear surface, respectively, when the SiO2 layer was etched up to 2 nm at the top surface.