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Polarization-resolved infrared techniques have been applied to study the optical properties of the quasi-two-dimensional electron gas in doped InGaAs quantum wells and to show that inter- and intrasubband processes can be distinguished by their polarization sensitivity. Distinct excitations of inter- and intrasubband transitions at the Γ(q=k=0) point in delta-doped narrow InGaAs/AlAs single quantum wells were resolved through the use of quantum well structures designed to increase their energy difference and thus diminish the coupling between these two processes. Longitudinal qz intrasubband plasmons were observed at 1550 cm−1 and were excited by transverse-magnetic (TM) polarized light; the intersubband transitions occurred at around 4000 cm−1 and were both transverse-electric (TE) and TM polarization active.
Peng et al. (1993) studied this question.