טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentYosef Michaeli
SubjectFermi Edge Polaritons Formed by Electron-Hole Pairs
Interacting with Cavity-Confined Photons
DepartmentDepartment of Physics
Supervisor Professor Emeritus Cohen Elisha
Full Thesis textFull thesis text - English Version


Abstract

Semiconductor microcavities (MC) are structures consisting of a heterostructure, such as a quantum well (QW) or a heterojunction, which are embedded between two high reflectivity distributed Bragg reflectors (DBR). Recently, reflection and photoluminescence (PL) spectroscopy studies of such structures containing a two dimensional electron gas (2DEG) have been reported, revealing sharp polaritonic lines, 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. We present a theoretical framework for the modeling of MCs with embedded QWs, and investigate the interaction of such electron-hole pairs with the light field excitations within these structures near the Fermi edge. First we consider the electronic properties of a bare QW via a two-level k.p method, where the 2DEG influence is incorporated through a self-consistent the Schrödinger-Poisson model. Light-matter interaction in the QW is modeled via a semi classical approach.

We assume a dipole light-matter interaction, and discuss two approximated methods for optical properties of the considered QW: (a) the free-carrier model and (b) the screened Coulomb-correlated model, where we incorporate both the Coulombic interactions between the charge carriers and also discuss the mutual screening effect. This calculation is performed with and without the presence of the 2DEG in the well region of the QW, yielding the complex electrical susceptibility, absorption and spontaneous emission spectra of the investigated of the structure.

Next, the obtained electronic and optical properties of a bare QW are then used to calculate the   reflection spectra of the full MC structure, with QW embedded in their cavity region. This is achieved by using the refractive index spectrum of the QW in the transfer matrix calculation of the entire MC reflection spectrum. Finally, the formulated approach is utilized to calculate the reflection anti-crossing curves of the investigated MC structures, which are analyzed manually and through a fitting procedure to the coupled-oscillator model.

We show that the strong interaction of the cavity-confined photon with the interband excitations of the two dimensional electron gas leads to the formation of cavity polaritons. The most significant result is the demonstration that cavity polaritons are indeed formed for high 2DEG densities at the Fermi edge energies. The coherence between all these e-h pair excitations is induced by the strong interaction with the cavity mode, in contrast with the exciton-polaritons case, where the coherence stems from the Coulomb interaction between the electron and hole.