טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentGuliamov Rahamim
SubjectMicrowave and Magneto-Optical Studies of the GaAs Quantum
Structures
DepartmentDepartment of Chemistry
Supervisor Professor Efrat Lifshitz


Abstract

Low-dimensional semiconductor structures are at the forefront of basic solid state physics and applied research. Despite the great progress in understanding quantum well band structures and exciton phenomena in undoped quantum wells, more information is needed about photoexcited electrons and holes, and other photogenerated species. Namely, about their photogeneration, dissociation, recombination processes and their interaction.

            Our work mainly focused on the study of the photoluminescence (PL) spectrum resulting of the indirect recombination of barrier electrons and the two-dimensional hole gas (2DHG) that are excited in a structure of mixed type I - type II GaAs/AlAs quantum wells. This structure consists of alternating narrow and wide GaAs quantum wells (QW), and is distinguished by a staggered conduction band alignment that leads to a fast electron transfer from the narrow to the wide QW’s and a very slow hole transfer. Consequently, a 2DHG and a two-dimensional electron gas (2DEG) are formed in the narrow and wide QW’s, respectively. Their density is controlled by the photoexcitation intensity and is experimentally determined by fitting the band - shape of the wide well direct recombination PL spectra (in the range of 1010<ne<5x1011 cm-2) ,6,7,.  A small fraction of the electrons recombine radiatively with the 2DHG while they are in the lowest X subband of the AlAs barrier, and the resulting spectrum is investigated at T = 1.4 K and for various excitation intensities.  The indirect transitions consist of a no - phonon band and momentum conserving (zone - edge) phonon sidebands. All these bands are blue shifted with increasing photoexcitation intensity. This shift is well explained by calculating the lowest X subband energy in the electrostatic potential, generated by the separate 2DEG and 2DHG charges, as a function of their density.