No abstract

We successfully increased the haze value of zinc oxide (ZnO) films fabricated using metal–organic chemical vapor deposition (MOCVD) by conducting glass-substrate etching before film deposition. It was found that with increasing the glass treatment time, the surface morphology of ZnO films changed from conventional pyramid-like single texture to greater cauliflower-like multi texture. Further, the rms roughness and the haze value of the films increased remarkably. Using ZnO films with a high haze value as front transparent conductive oxide (TCO) films in hydrogenated microcrystalline silicon (µc-Si:H) solar cells, we improved the quantum efficiency of these cells particularly in the long-wavelength region.

Undoped, n- and p-type hydrogenated nanocrystalline cubic silicon carbide (nc-3C–SiC:H) films were successfully deposited on glass and silicon substrates at a low substrate temperature of about 300 °C by hot-wire chemical vapor deposition. The structural, optical, and electrical properties of the films were investigated by X-ray diffraction (XRD), Fourier transform infrared absorption (FTIR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry, photothermal deflection spectroscopy (PDS), and conductivity measurements. The XRD and FTIR measurements revealed a clear correlation between the average grain size and width of the SiC stretching mode vibration of the films. The dark conductivity of the films was increased from 5.8×10-11 to 6.2×10-6 S/cm with increasing the grain size from 6.4 to 16.6 nm. The detailed analysis of the dark conductivity indicates that the Fermi level position is affected by the grain size of the films. Spectroscopic ellipsometry measurements showed that the dielectric functions of the films are strongly affected by the grain size. The n- and p-type nc-3C–SiC:H films were also successfully deposited using phosphine, hexamethyldisilazane, and dimethylaluminumhydride as dopants. For the n- and p-type films, the dark conductivities of 5.32×10-0 and 7.67×10-4 S/cm were achieved, respectively. The optical absorption spectra of the doped films indicate that p-type doping significantly affects absorption coefficients above the bandgap of nc-3C–SiC:H compared with n-type doping. For the n-type films, the absorption coefficients below the bandgap are affected by free carrier absorption as well as by localized states within the bandgap.

Heterojunction p-Cu2O/n-β-Ga2O3 diodes were fabricated on an epitaxially grown β-Ga2O3(001) layer. The reverse breakdown voltage of these p-n diodes reached 1.49 kV with a specific on-resistance of 8.2 mΩ cm2. The leakage current of the p-n diodes was lower than that of the Schottky barrier diode due to the higher barrier height against the electron. The ideality factor of the p-n diode was 1.31. It indicated that some portion of the recombination current at the interface contributed to the forward current, but the diffusion current was the dominant. The forward current more than 100 A/cm2 indicated the lower conduction band offset at the hetero-interface between Cu2O and Ga2O3 layers than that predicted from the bulk properties, resulting in such a high forward current without limitation. These results open the possibility of advanced device structures for wide bandgap Ga2O3 to achieve higher breakdown voltage and lower on-resistance.

We investigated hydrogenated aluminum oxide (a-Al1-xOx:H) as a high quality rear surface passivation layer of crystalline silicon solar cells. The a-Al1-xOx:H films were deposited by plasma-enhanced chemical vapor deposition (PECVD) using a mixture of trimethylaluminum (TMA), carbon dioxide (CO2), and hydrogen (H2) at a low substrate temperature of about 200 °C. The ratio of CO2 to TMA during deposition and thermal annealing after the film deposition are the key factors in achieving high quality passivation. A 28-nm-thick a-Al1-xOx:H film deposited by PECVD showed a low surface recombination velocity of about 10 cm/s.