Photoacoustic spectra of ZnO-CoO alloy semiconductors

Photoacoustic spectra (PA) of Zn1-xCo2O alloy semiconductors sintered as po wdered samples were measured to estimate the optical absorption. Photoacous tic spectroscopy (PAS) is insensitive to the light scattering effects on th e samples. CoO molecular percentages in the alloy were changed from 0 to 20 mol%. The samples were sintered at 600 or 950 degreesC for 24 h in a quart z glass tube. From the PA spectra in the short wavelength region. we plotte d (phv)(2) vs hv and estimated the band-gap energy (E-g) of the alloy semic onductors. where rho is the PA signal intensity and hv is the excitation li ght photon energy. E-g of ZnO-CoO alloy decreases as the COO content increa se and reaches to 2.19 eV in the 20mol% CoO sample. Although the band-gap v ariation in the lower-CoO-content samples (COO content below 10mol%) is lar ge, it becomes small in the high COO concentration samples. This result con curred with the result of dissolving COO in ZnO as obtained by X-ray diffra ction measurement.