Raman, photoluminescence and modulation spectroscopy of semiconductor heterostructures

Collective and localized excitations in semiconductor heterostructures can be discovered and delineated with a number of spectroscopic techniques. When subjected to an alternating strain, the piezomodulated optical properties display signatures characteristic of electronic transitions. Results for single, double, and multiple quantum wells in GaAs/Al(x)Ga(1-x)As quantum well structures reveal electronic transitions in the wells, the barriers, and the buffer layer with exceptional clarity. Raman scattering in a single quantum well of GaAs sandwiched between Al(x)Ga(1-x)As layers reveals longitudinal optical (LO) phonons confined to the well, resonance of the scattered radiation with the electronic transitions of the well being exploited. The frequencies of the confined LO phonons agree well with these deduced from the bulk dispersion of GaAs. Also observed in the Raman spectrum of superlattices of such structures are the interface optical phonons. Raman spectroscopy applied to heterostructures of diluted magnetic semiconductors show zone folded acoustic phonons, propagating and confined optical phonons, and interface optical phonons. The large magnetic field shifts in the photoluminescence associated with the electron transition in the quantum wells demonstrate the existence of large exchange interaction between the band electrons and the magnetic ions, as in the bulk. Magnetic excitations in diluted magnetic semiconductor heterostructure will be discussed.