E. Ribeiro et al., An optical study of self-assembled InxGa1-xAs/GaAs quantum dots embedded in a two-dimensional electron gas, J APPL PHYS, 87(11), 2000, pp. 7994-7998
We studied the low temperature (77 K) photomodulated reflection and transmi
ssion as well as the photoluminescence at 2.2 K of a self-assembled InxGa1-
xAs quantum dot layer grown on a (100) GaAs substrate in the vicinity of a
two-dimensional electron gas. The dot layer was grown without rotation of t
he substrate in order to achieve a gradual variation of the In concentratio
n along the wafer diameter. This resulted in an increase in the density of
quantum dots along the In concentration gradient, which is reflected in a c
haracteristic dependence of the relative intensities of the spectral lines.
A consistent assignment of the optical structure observed in all spectra l
eads to an estimate of the average value of the Fermi energy in the conduct
ion band of the wetting layer (E(F)similar or equal to 13.4 meV). The varia
tion of this Fermi energy along the composition gradient can be obtained fr
om the spectra, and an estimate of the gradient of the density of quantum d
ots along this direction can be made. A careful comparison of the variation
of the critical energy of the different lines suggests that the average qu
antum dot size depends on the In molar fraction of the alloy, which is seen
to vary more or less linearly across the wafer diameter. (C) 2000 American
Institute of Physics. [S0021-8979(00)06510-5].