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Basak, Amlan Kumar (2010) ULTRAFAST CARRIER AND LATTICE DYNAMICS STUDIES IN GaAs WITH INTENSE OPTICAL EXCITATION. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Detailed understanding of basic scattering mechanisms of high density and highly energetic carriers (electrons and holes) are important for future semiconductor device technology. During these scattering processes carriers interact among themselves and with the lattice. Most of the scattering events occur in few tens of femtoseconds to picosecond timescale. Ultrafast lasers, with improving performance, make it possible to observe these fundamental interactions as they happen and detailed study on them becomes possible.Here we present ultrafast carrier and lattice dynamics studies in the technologically important III-V semiconductor GaAs. We performed ultrafast pump-probe spectroscopy in transient reflection and reflective electro optic sampling geometries on n-doped GaAs with 10^18-10^20 cm^-3 photoexcited electron-hole pair density. Coherent phonons and plasmons are generated in the semiconductor as a result of interaction between the photocarriers and the lattice; they modulate the dielectric properties of the sample, which can be detected by measuring transient reflectivity. By varying the excitation laser fluence, we varied the excited carrier density and measured the response of the semiconductor at different photoexcited carrier density levels. Detailed analysis of density dependent response sheds light on generation mechanism of coherent phonons and plasmons and subsequent dynamics and transport. Further analysis using a dielectric response model shows that the carrier density dependent coupled plasmon-phonon dynamics represents the hole plasma response. We also performed symmetry selective generation and detection of coherent phonons and plasmons by exciting and probing the crystal along different crystallographic directions. These results tell us about the dominating processes responsible for the generation and detection of these modes. We further analyzed the changes in the frequency response with time and probed the plasmon-phonon response at various photon energies of the exciting and probing pulse. Time dependent frequency of the coupled plasmon-phonon mode indicates transient changes in the plasma density, most likely involving transport of the interacting carriers from the observed region on the sample.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Basak, Amlan
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairPetek, Hrvojepetek@pitt.eduPETEK
Committee MemberSnoke, David Wsnoke@pitt.eduSNOKE
Committee MemberChen, Kevin Ppec9@pitt.eduPEC9
Committee MemberDevaty, Robert Pdevaty@pitt.eduDEVATY
Committee MemberLiu, W.
Date: 28 September 2010
Date Type: Completion
Defense Date: 22 July 2010
Approval Date: 28 September 2010
Submission Date: 12 July 2010
Access Restriction: 5 year -- Restrict access to University of Pittsburgh for a period of 5 years.
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Physics
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: carrier density; coherent phonon; coupling; gallium arsenic; plasmon; semiconductor
Other ID:, etd-07122010-152325
Date Deposited: 10 Nov 2011 19:50
Last Modified: 15 Nov 2016 13:45


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