Magnetophotoconductivity studies of ${\mathit{D}}^0$ and ${\mathit{D}}^{\mathrm{-}}$ centers in GaAs quantum wells in metallic and insulating states

${\mathit{D}}^0$ and ${\mathit{D}}^{\mathrm{-}}$ states in GaAs quantum wells are studied simultaneously by far-infrared magnetophotoconductivity. In high magnetic fields, the observed sharp transitions are attributed to transitions between ground and excited states of ${\mathit{D}}^0$ and ${\mathit{D}}^{\mathrm{-}}$ centers, respectively. In low magnetic fields, the spectra are dominated by free-electron response. The changes in spectral responses are explained in terms of a magnetic-field-induced metal-insulator transition of the ${\mathit{D}}^{0\mathrm{-}}$${\mathit{D}}^{\mathrm{-}}$ band.