What is the bandgap value of SiO2?
For thermally grown amorphous $\ce{SiO2}$ films, a bandgap of 9.3 eV was measured by Weinberg.

Measurements on $\alpha$-quartz by Calabrese give $E_g(\Gamma)$ = 6.3 eV, compared to 9.2 eV calculated by Chelikowsky and Schlüter.

Calculations by Ramos on $\beta$-cristobalite with the space groups $Fd3m$ (face-centred cubic, fcc), $I\bar{4}2c$ (body-centred tetragonal, bt), and $P2_13$ (simple cubic, sc) gave direct bandgaps of $E_g(\Gamma)$ = 5.48, 5.79 and 5.73 eV, respectively.