Low temperature wavelength-modulated reflectivity measurements of isotopically engineered $\mathrm{ZnO}$ samples have yielded the dependence of their A, B, and C excitonic band gaps on the isotopic masses of Zn and O. The observed dependence is analyzed in terms of the band gap renormalization by zero-point vibrations via electron-phonon interaction and the volume dependence on isotopic mass. A simplified, two-oscillator model, employed in the analysis, yields zero-point renormalizations of the band gaps, $-154\pm 14\mathrm{meV}$ (A), $-145\pm 12\mathrm{meV}$ (B), and $-169\pm 14\mathrm{meV}$ (C), for $\mathrm{ZnO}$ with natural isotopic composition.

• Received 4 May 2006

DOI:https://doi.org/10.1103/PhysRevB.74.165203