Fermi-edge-induced magnetophotoluminescence in high-carrier-density single heterojunctions

Fermi-edge-induced excitonic magnetophotoluminescence (MPL) of second (${\mathit{n}}_{\mathit{c}}$=2)-subband electrons and photoexcited holes X(${\mathit{n}}_{\mathit{c}}$=2,h) is reported in high-carrier-density GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As single heterojunctions for two-dimensional carrier densities in the range (6.6–16.2)×${10}^{15}$ ${\mathrm{m}}^{\mathrm{-}2}$. The MPL shows magneto-oscillatory behavior of intensity, photon energy, and peak width. Furthermore, ${\mathit{n}}_{\mathit{c}}$=2 subband recombination with light holes X(${\mathit{n}}_{\mathit{c}}$=2,l) is reported. A splitting of the X(${\mathit{n}}_{\mathit{c}}$=2,h) is reported at low carrier density, which results from the separate interaction of the two spin-split states of the ${\mathit{n}}_{\mathit{c}}$=1 Landau level in which the Fermi level resides on the second subband. The dependence of the spectra on both excitation density and temperature indicates strongly that photoluminescence (PL) from the ${\mathit{n}}_{\mathit{c}}$=3 subband occurs. PL originating from the two-dimensional electron gas (2DEG) and that from the GaAs buffer layer could be distinguished by excitation below and above the GaAs band gap. In the highest-carrier-density sample, evidence is found for the formation of a band of localized states betwen the spin components of a Landau level. Recombination occurs between the exponentially decaying tails of the photoexcited holes, which relax to the flat-band region of the GaAs. Additional information on the 2DEG was obtained via resonant-excitation experiments. Phonon replicas of both the second-subband exciton and the unpopulated third subband are observed. The latter very sharp replica appears if a nonequilibrium electron concentration is created in the resonantly excited third subband. Resonant excitation also reveals the recombination of electrons in the ${\mathit{n}}_{\mathit{c}}$=2 subband with holes located at neutral acceptors. Strong indications were found for PL of the ${\mathit{n}}_{\mathit{c}}$=1 lowest Landau level upon resonantly exciting the X(${\mathit{n}}_{\mathit{c}}$=2,h) transition in the lowest-carrier-density sample.