טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentGabbay Alon
SubjectFermi Edge Polaritons in a Modulation Doped Quantum Well
Embedded in a Microcavity: The Effect of a Two-
Dimensional Electron Gas
DepartmentDepartment of Physics
Supervisor Professor Emeritus Elisha Cohen
Full Thesis textFull thesis text - English Version


Abstract

 Semiconductor microcavities (MC) are structures consisting of a cavity layer cladded by a distributed Bragg reflector on each side. A heterostructure, such as a quantum well (QW) or heterojunction, is embedded within the MC. In these structures the

photon mode is spatially confined inside the cavity layer. When the cavity layer width is comparable to the exciton wavelength , the exciton energy matches the confined photon energy, and a resonant interaction takes place. The interaction strength can be

described in two regimes: (a) the weak coupling regime where this interaction can be described by perturbation theory. (b) The strong coupling regime, where the system eigenenergies are admixed exciton-photon states (termed cavity polaritons) and a Rabi

splitting between them is observed .

In this work, we study, by reflection and photoluminescence (PL) spectroscopy, polariton formation and the effect of a magnetic field on these cavity polaritons in a structure containing a two-dimensional electron gas (2DEG). The structure used is a

modulation doped quantum well (MDQW), which is a type I GaAs QW , with a thin layer of Si doping within the wide bandgap material . At equilibrium, charge transfer occurs from the Si layer to the QW, in order to equalize the chemical potential on both sides . Hence the ground state of the system is a 2DEG in the quantum well. The effect of a magnetic field on a 2DEG embedded in a microcavity is compared with that on a bare MDQW .

The main observations of this study are: (a) Reflection measurements from a MDQW embedded in a MC exhibit sharp polaritonic lines. These polaritons are composed of a cavity photon which is in strong interaction with unbound electron-hole (e-h) pair excitations, located at the Fermi edge of the 2DEG. (b) The coherence between all these e-h pair excitations, which is required for strong interaction, is induced by the strong interaction with the cavity mode. This is in contrast to exciton-polaritons, in which the coherence between the e-h transitions stems from the Coulomb interaction between the electron and hole. (c) Measurements under an applied magnetic field provide further evidence for the ability of the confined cavity mode to interact strongly with unbound e-h pair excitations .