OPTICAL REFLECTANCE OF ALUMINUM-DOPED ZINC-OXIDE POWDERS

Changes in the electronic properties of zinc oxide powders doped with aluminum were related to the optical reflectance characteristics. ZnO powders doped as a solid solution, having from 0.035 to 1.00 mol % Al, were characterized. Diffuse optical reflectance was measured over near-ultraviolet and visible wavelengths from 340 to 700 nm. Diffuse infrared reflectance was used to characterize the free-electron density in each powder. Free-electron densities ranged from 2.5 x 10(14) cm-3 for undoped ZnO to 3.5 x 10(17) cm-3 for the 1.00-mol % Al powder. The Al-doped powders showed significant resistance to color center formation, whereas the undoped powder did not. The suppression of the optical absorption at approximately 400 nm in the Al-doped powder may be related to the suppression of a band state to localized defect state charge transfer.