Abstract
The binding energy of residual donors in nominally 300-Å-wide GaAs/As quantum wells has been determined from the results of low-temperature photoluminescence (PL), PL-excitation (PLE), and resonant-excitation (RE) measurements. The center of each quantum well was δ doped with 3× Be acceptors, resulting in ionization of residual donors and allowing the observation of free-heavy-hole-to-donor (,h) transitions. The n=1 (,h), transition for center-well donors was observed in PL, and the n=2 (,h) transition for center-well donors was observed in PLE. Two transitions associated with (,h) were observed in PLE; it is proposed that both the 2s and 2 excited states of the donor are being observed. The calculated binding energy of the 2s and 2 excited states can be added to the measured transition energy from the heavy-hole subband to the respective excited states. This method gives a donor binding energy of 8.0±0.5 meV. The calculated binding energy of the donor for a 300-Å-wide well is 8.7 meV according to Greene and Bajaj. The observed energy separation between the 2s and 2 excited states of the donor is 0.7 meV, in reasonably good agreement with the calculated value of 0.5 meV. We note that this work is an observation of the n=2 state of the donor from PLE spectra, as well as the detection of the 2s and 2 levels.
- Received 8 April 1991
DOI:https://doi.org/10.1103/PhysRevB.44.8869
©1991 American Physical Society