Definitive identification of ${\mathit{D}}^{\mathrm{-}}$ centers in GaAs quantum wells by tilt-induced line splitting in a magnetic field

${\mathit{D}}^{\mathrm{-}}$ centers have been unambigously identified in GaAs/(Ga,Al)As quantum wells by analysis of the dependence of the observed photoconductivity spectrum on the applied magnetic field and sample orientation. Theoretical investigations show that in magnetic fields of interest the ${\mathit{D}}^{\mathrm{-}}$ transitions do not involve photoionization of the centers as has been previously supposed but proceed from the ground state to discrete ${\mathit{p}}_{\mathrm{-}1}$- or ${\mathit{P}}_{+1\mathrm{}}$-like ${\mathit{D}}^{\mathrm{-}}$ levels, which lie above the N=0 and N=1 Landau-level energies, respectively. Tilting the sample leads to a predicted anticrossing of discrete ${\mathit{p}}_0$- and ${\mathit{p}}_{+1\mathrm{}}$-like ${\mathit{D}}^{\mathrm{-}}$ levels. Excellent agreement with experiment is obtained without any adjustable parameters.