Electronic Structure And Optical Polarization Anisotropy Of Self-Organized Inas/Gaas Quantum Dots

The lack of precise information regarding the shape of self-organized InAs/GaAs QDs has been a key obstacle in the development of optoelectronics technology based upon these structures. This knowledge is necessary to quantitatively model the electronic structure, optical spectra, and relaxation dynamics - all key parameters in the design of QD-based optoelectronic devices. We have recently determined the shape of self-organized InAs/GaAs quantum dots (QDs), based upon an intensive study utilizing RHEED, TEM and atomic force microscopy. Our results indicate that the bounding facets of InAs/GaAs quantum dots are of the {136} family. The resulting pyramidal structure possesses a parallelogram base that is substantially elongated along [1-10] and thus is characterized by C2v symmetry, quite different from square-base pyramidal or lens-shaped geometries which have been previously assumed. In this paper the relationship between the shape and the optical properties of self-organized InAs quantum dots is discussed. PL spectra exhibit multiple excited state transitions, each of which are linearly polarized, an experimental fact which is inconsistent with previous shape models of InAs/GaAs QDs. A coupled-band electronic structure calculation of {136}-bounded QDs is presented to show that the optical polarization anisotropy can be understood quantitatively by consideration of the true shape of the QD structures. Our main conclusion is that the spectral polarization anisotropy provides a signature which is uniquely sensitive to shape; polarization measurements provide a more stringent rest of electronic structure models than simple comparison to PL peak positions.