The PL spectra of and samples at 3.6 K temperature at two different laser excitation intensities of and . The symbols and indicate the and exciton transitions, indicates the exciton-polariton, and —the donor and acceptor bound exciton transitions. is the free electron-neutral residual acceptor transition, and depict the first and the second phonon replicas. , and indicate the residual donor to residual acceptor transitions and its first and second LO-phonon replicas. is the first emission band. is the second emission band with the first, and second LO-phonon replicas. is the energy of the LO-phonon in GaAs.
The PL spectra of the sample (top curve) and the -GaAs active layer of the same structure (bottom curve) at 3.6 K and a laser excitation intensity of . The inset shows the exciton region of the PL spectrum in a linear scale of PL intensities. The symbol QW indicates a band of the PL spectrum emitted from quantum wells grown in a buffer layer. The symbols and denote heavy-hole and light-hole excitonic transitions. marks possible defect-related PL emission band and marks recombination of free electrons with free holes. The other symbols are identical to those of Fig. 1.
The PL spectra of the sample at different temperatures from 3.6 to 150 K and at a laser excitation intensity of . The spectra are shifted along the vertical axis for clarity. The symbols are identical to those of Fig. 1.
Dependence of spectrally integrated PL of the sample on an excitation intensity at 3.6 K (open circles) and 12 K (solid circles). The dashed line is a guide line of the square law dependence. Experimental data at 12 K is shifted up by three orders along vertical axis for clarity.
Temperature dependence (a) of spectrally integrated PL of the sample. (b) Lorentzian approximation of FWHM of excitonic line (open circles) and exciton-polariton line (open triangles). The dashed line is a linear approximation of FWHM of the excitonic line at low temperatures.
The dependence of Lorentzian approximation FWHM of excitonic line (circles) and exciton-polariton line (triangles) on laser excitation intensity of sample at 12 K (a) and 3.6 K (b) temperatures.
The PL spectra of the sample at different laser excitation intensities and of the -GaAs layer of the same structure (two bottom curves) at 3.6 K. The symbols are according to Figs. 1 and 2.
Numerical calculations of the energy band diagram (top), electron concentration (middle) and built-in electric field (bottom) of the sample (a) and the sample (b). Surface potential of was used in the calculations.
Sample parameters and summary of characteristics. is the thickness of Si-doped layer, is the doping concentration, is sheet electron concentration measured at 300 K, is the thickness of spacer layer, represents excitonic line amplification coefficient and symbols represents FWHM of the excitonic line. (*Selectively doped heterostructure without specially prepared buffer layer.)
Energies of various transitions in MBE-grown GaAs epitaxial layers observed in the PL spectrum at low temperatures collected from different sources.
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