PHOTOGENERATED CARRIER DYNAMICS IN SEMICONDUCTOR QUANTUM WELLS.
Item
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Title
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PHOTOGENERATED CARRIER DYNAMICS IN SEMICONDUCTOR QUANTUM WELLS.
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Identifier
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AAI8801762
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identifier
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8801762
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Creator
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SHUM, KAI.
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Contributor
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R.R. Alfano
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Date
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1987
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Electronics and Electrical
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Abstract
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Subpicosecond laser and streak camera technologies and steady state photoluminescence spectroscopy were used to investigate the ultrafast dynamics of photogenerated carriers and hot-phonons in III-V undoped GaInAs and GaAs quantum well structures fabricated by state-of-art MBE technique as well as in II-VI CdS{dollar}\sb{lcub}\rm x{rcub}{dollar}Se{dollar}\sb{lcub}\rm 1-x{rcub}{dollar} spherical quantum wells.;We have demonstrated what experimental data from optical transitions should be used in order to determine the band offsets in the sensitive zone of well thickness ranging from 15 to 80A. A critical discussion on the creditability of our model is given.;A theoretical study on the electron scattering rate by LO phonon was carried out by treating phonon momentum in the confined z-direction as a ramdom variable. The calculated results show that the emission rate at the onset of phonon emission is 3 times smaller than previously reported and has a weak well width dependence. The experimentally observed variation of carrier temperature with well thickness using photoluminescence indicates that the phonon scattering rate for carriers confined in quantum wells does not strongly depend on the well width within our experimental accuracy.;Time-resolved photoluminescence from an undoped GaAs multiple symmetric and a single asymmetric quantum well structures at 4K excited by 500fs laser pulse were measured by a streak camera detection system with 2ps time resolution. The hot-phonon effect on energy relaxation of hot carriers is experimentally verified. We have found that hot-phonons are responsible for the ultrafast carrier density decay within the first 30ps after the end of 500fs laser pulse excitation. The diffusivity D of photoexcited carriers in the asymmetric well has been directly determined to be 10{dollar}\sp{lcub}6{rcub}cm\sp2/ s{dollar} at 4K, which is about four orders magnitude larger than the thermodynamic value in bulk GaAs.;The recombination lifetimes for the radial and angular quantum number conserved {dollar}1S\to 1S{dollar} and {dollar}1P\to 1P{dollar} transitions in CdS{dollar}\sb{lcub}\rm x{rcub}{dollar}Se{dollar}\sb{lcub}\rm 1-x{rcub}{dollar} spherical quantum wells (quasi-OD) were measured by time-resolved and steady-state photoluminescence spectroscopy and compared with theory.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Engineering
