Photoluminescence and Hall characterization of pseudomorphic GaAs/InGaAs/AlGaAs heterostructures grown by molecular-beam epitaxy
Hall electrical properties measured by the van der Pauw method and low-temperature photoluminescence (77 K PL) spectra of pseudomorphic GaAs/InyGa1-yAs/AlGaAs modulation-doped field-effect transistor-type heterostructures grown by molecular-beam epitaxy were compared. By using these two characterization methods, the influences of the growth temperature T(s), the InGaAs quantum-well channel thickness d(ch), and its indium composition y were studied. Interesting correlations were established between their 77 K PL spectra and their transport properties measured either in the dark or under white-light illumination. The PL spectra exhibit one or two bands which are attributed to transitions from electronic states belonging to the first or to the second subband formed in the conduction quantum well, the second transition at higher energy being observed only when the two-dimensional concentration exceeds a critical value n(c) which, in the dark, is approximately 2.4 X 10(12) CM-2 (i. e., d(ch) almost-equal-to 108 angstrom) for the homogeneously doped heterostructures with y=0.25.