טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentBen Isaac Eyal
SubjectEffect of Excitation Intensity on the Polariton Spectrum in
Microcavities Containing a 2D Electron Gas
DepartmentDepartment of Physics
Supervisor Professor Emeritus Elisha Cohen


Abstract

The objective of this work is to study the spectroscopic properties of a 2DEG generated in a modulation doped quantum well (MDQW) that is embedded in a microcavity (MC) structure, under the influence of external light sources:1. Above barrier excitation (a HeNe laser) that depletes the 2DEG. 2. Resonant excitation (Ti-sapphire laser) that is used to increase the density of the electron-hole pairs. 3. White light source (Halogen-Tungsten lamp) that is used as a probe beam for the reflection spectra .


It is known that in GaAs MDQW, above the critical 2DEG density ne = 5x1010cm-2 the screening effect is strong enough to prevent the formation of excitons. This study demonstrate that for a 2DEG density ne = 1011cm-2 exciton like-lines are photoexcited. The reflection spectra exhibit a strong interaction regime, and a Rabi splitting of about 1.5meV is observed. This is done by utilizing the strong confined photon-exciton interaction in a MDQW/MC system .


Additional observation of this study are: (a) The enhancement of the PL line over the reflection line, when the lasers are introduce and the cavity photon mode is in resonance with the lowest exciton level. (b) For excitations where just the above barrier laser is varied, the integrated PL spectra exhibit a transition from sub linear to super linear behavior, depending on the cavity energy. (c) When the intensity of the above barrier is increased above 0.5meV/cm2 PL lines are observed at higher polariton energy levels. This means that the recombination process is more significant than the thermalization process. (d) The

coupling strength was extracted using coupled oscillator model and it appeared to be constant with a value of about 1.5meV .