Optical studies of low-dimensional semiconductors
During my graduate studies, I have identified for the first time
the Negatively Charged Exciton line in GaAs quantum wells. This and other
results are summarized below.
We have identified the negatively charged excitons in a dilute 2D electron
gas [G. Finkelstein et al., Phys. Rev. Lett. 74, p. 976 (1995)]. It was
the first correct identification of this complex in GaAs. In fact, the
charged exciton line had been reported in many earlier publications on
nominally undoped GaAs quantum wells, but was erroneously ascribed to biexcitons,
impurity or well-width-fluctuations bound excitons, "dark" excitons etc.
Later on we completed the list of the charged intrinsic complexes in quantum
wells by the observation of the positively charged excitons [G. Finkelstein
et al., Phys. Rev. B53, p. R1709 (1996)]. We extensively studied the properties
of these complexes at zero and high magnetic fields. In particular, we
compared the radiative lifetimes of the neutral and negatively charged
excitons by the resonantly excited time-resolved photoluminescence. This
unique technique allowed us to investigate in detail the highly nonequilibrium
dynamics of the neutral-charged excitons system and to extract the formation
time of the charged excitons [G. Finkelstein et al., Phys. Rev. B58, p.
2DEG at the transition to the localized regime:
|Photoluminescence spectra of a gated 2D
electron gas at different gate voltages (and
hence electron densities). The localization
transition at -1.5 V shows up as an abrupt
change in the spectra.
We simultaneously studied optical and transport properties of a gated
2D electron gas at low densities. We observed a strong correlation between
changes in the local characteristics (as probed by photoluminescence) and
abrupt drop of the electron conductivity [G. Finkelstein et al., Phys.
Rev. Lett. 74, p. 976 (1995)]. This correlation indicates that in the 2D
electron gas the change of the microscopic properties gives rise to the
onset of localization.
Shakeup processes in the photoluminescence of a 2DEG:
We have studied the shakeups in the photoluminescence spectra of a
2D electron gas at high magnetic fields. In shakeup processes the recombining
electron-hole pair creates excitations (magnetoplasmons) in the 2DEG. These
processes, proved out to be extremely sensitive to the details of the many-body
interactions in the 2D electron gas [G. Finkelstein et al., Phys. Rev.
B56, p. 10326 (1997)]. Observation of the shakeup lines in the recombination
spectra of the negatively charged exciton directly proves that it is indeed
a three-particle complex [G. Finkelstein et al., Phys. Rev. B53, p. 12593