טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentMagidson Valentin
SubjectFano-Type Interference in the Raman Spectrum of Photo-
Excited Silicon
DepartmentDepartment of Physics
Supervisor Professor Emeritus Robert Beserman


Abstract

In this work, we present an optical study of the photoexcited electron-hole plasma in silicon. In particular, we report on the asymmetric Fano-type line shape in the Raman spectrum of the silicon under high continuous wave excitation intensities. This line shape is attributed to interference between Raman scattering processes of phonon and of photoexcited holes. We show that the Fano resonance phenomenon provides a tool for measuring the electronic density by means of Raman light-scattering, which is more conventionally used for studying phonon modes of the crystal lattice. We demonstrate a new method, which allows determining precisely the electron-hole plasma density from the Raman measurements. We thus suggest a new tool for better characterization of a physical system, which is both theoretically and technologically important. In our studies, the laser beam is tightly focused to a sub-micron spot. The heat transfer from this spot is three-dimensional, and thus very efficient. We achieved optically excited free carrier plasma concentration of 3*1019cm-3 with sample heating of only 1000C. The density of the free carrier plasma was carefully estimated by comparison with the Raman scattering spectra of heavily doped samples in a wide range of temperatures. In order to verify our Raman measurement results, we simultaneously performed complimentary experiments. We spatially resolved the photoluminescence and the modulated transmission of the photoexcited samples. The Fano interference effect is well known in other fields of physics. It occurs in many systems in which a discrete spectrum interferes with a continuous one. This work provides an excellent test system for the effect itself. Namely - high purity photo-excited  bulk silicon.