Aluminum nitride/indium nitride bilayer and multilayer thin film systems as coatings for solar cells and longwave-pass filters

The optical properties of sputtered AlN/InN/bilayer and multilayer thin film systems onto quartz substrates have been investigated in the visible and near infrared (NIF) regions. The designed multilayer was optimized at 500 nm and 50 -70 incidence for bilayers of alternate high and low index configuration. Analysis of these designs revealed that by increasing number of layers the reflectivity decreased to very low values (0%-8%) over a broad range of wavelengths (300-1400 nm). The transmissivity tended to increase smoothly from about zero at 750 nm to 88% in the NIR region while the absorptivity showed a tendency to decrease with increasing wavelength in the same region. Also, we found that the absorptivity increases with the total physical thickness of the multilayer system over the visible spectra (20% - 99%). Therefore, the nitride bilayer and multilayer systems could be used as a longwave-pass filter. However, since these systems provided extremely high absorptivity anywhere within the visible spectra they could be used as coatings for solar cells. X-ray diffraction (XRD) spectra of AlN/InN/quartz multilayer systems were measured. The XRD patterns of the systems revealed a polycrystalline structure with a strong InN (002) diffraction peak at 31.2 . (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)