Effects of Confinement on Shallow Donors and Acceptors in GaAs/AlGaAs Quantum Wells

Far-infrared magnetospectroscopy at low temperatures has been used to study MBE-grown GaAs/AlGaAs quantum wells selectively doped with donors (Si) and acceptors (Be). Measurements on samples doped with donors over different regions of the GaAs wells have demonstrated dramatic differences in absorption line profiles attributed to dopant redistribution during growth. These measurements are capable of resolving impurity position along the growth direction within about 10 Å. Samples doped in the well and the AlGaAs barriers display strong absorption features attributed to electrons in the wells bound to parent ionized donors in the barriers. Quantum wells doped with acceptors in the well centers display absorption features displaced to higher energies compared to similar measurements on bulk epitaxial layers. The magnetic field and temperature dependence of the absorption in both QW and bulk samples have been used to elucidate the effects of the confinement on the acceptors.