The SiO<sub>x</sub>/Si quantum wells (QWs) structures were fabricated by using the successive deposition technique, as quantum confinement device to increase the effective energy bandgap and passivation effect in Si surface for the third generation solar cell applications. In Si/SiO<sub>x</sub> QWs, the thicknesses of Si layers and SiOx layers were varied between 1 to 5 nm, respectively. The roughness of sputter-deposited Si on SiO<sub>x</sub> was less than 4 Å in the thickness of 2 nm. By using the SiO<sub>x</sub>/Si QW structures on Si surfaces, the lifetime measured by u-PCD technique increased as a result of passivated surface effects. The tunneling phenomena and good interface properties were observed in the fabricated QWs structures.
Mechanically grooved silicon solar cells with buried contact copper electrode were attempted. In order to groove a simple mechanical grooving system was home-made, in which synchronous motors in hard disc driver (HDD), audio amplifier, signal generator were used. For the anti-reflection films sputtering condition for SiN<sub>x</sub> films was optimized. With increasing input power, pressure, index of refraction of the films increased so that a very low etching rate of 0.8 nm/min could be achieved with a condition of Ar and N<sub>2</sub> flow rate of 5 SCCM, input power of 300 W and sputtering pressure of 1 × 10<sup>-2</sup> torr. Annealing condition for the formation of nickel silicie from electroless plated Ni-P layer was optimized as well as plating condition of copper electrode. However, the conversion efficiency of the BCSC in this study is 3.6% which is unexpectedly small. It seems that the reason for the low efficiency is due to short circuit forming in the lancet of the pyramid.
A cholesteric liquid crystal cell was fabricated possessing 1-D photonic bandgap structure. From the measurement of the linear absorption spectrum of the cell, a bandgap was identified, centered at 1.08 eV (1143 nm) with the gap width of 0.1 eV (100 nm). Based on the linear absorption spectra, the dispersion of the principal refractive indices along the parallel and perpendicular directions of the molecule was determined as 1.631 and 1.476 at the wavelength of 1064 nm through Berreman matrix method. A Q-switched Nd:YAG laser (1064 nm) was employed to investigate the nonlinear optical changes of photonic bandgap. As the laser intensity was increased to 320 MW/cm<SUP>2</SUP>, the transmittance decreased from 0.51 to 0.47, corresponding to an 8% change. The nonlinear transmittance change was analyzed numerically by Berreman matrix method with the incorporation of Kerr nonlinearity in the optical response of the molecules forming cholesteric liquid crystal. The changes in the refractive indices along the parallel and perpendicular directions were 3.46 and 1.51 X 10<SUP>-10</SUP> (cm<SUP>2</SUP>/W). The changes in the position and width of bandgap were 0.02 eV and 0.03 eV at the laser intensity of 320 MW/cm<SUP>2</SUP>.