A theory is developed for the luminescence linewidth in a quantum well made of ternaries when the two-dimensionally free excitons undergo alloy disorder scattering. The expression for linewidth shows a L-1 dependence on the well width L for infinite barrier height. For thin wells leakage of wave function into the barrier is considered. A comparison between the experimental data and the present values points out the dominant role of alloy disorder scattering. For wells thinner than 40 Å the calculated values decrease with decreasing well width, indicating the importance of surface roughness scattering.

P K BASU

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University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Linewidth of free excitons in quantum wells: Contribution by alloy disorder scattering

Applied Physics Letters

The expressions for absorption and luminescence linewidths of Wannier excitons in short-period superlattices are derived for several scattering mechanisms. The wave function of the 1s excitons is assumed to be a product of (i) a variational function describing relative motion of electrons and holes, and (ii) the envelope functions for the electrons and holes obtained from the Kronig-Penney model. The scattering rates are calculated by using Fermis golden rule for deformation potential, interface roughness, and alloy-disorder scattering. The linewidth due to interface-roughness scattering is also expressed by employing the self-consistent Born approximation. Numerical values presented for GaAs/Al0.3Ga0.7As superlattices indicate that the deformation-potential scattering is weak and that the alloy-disorder scattering is significant for lower values of the superlattice period. The most significant contribution to the linewidth comes from the interface-roughness scattering; the golden rule yields quite large values, whereas reasonable values are obtained from the self-consistent Born approximation. © 1992 The American Physical Society.

Physical Review B

Low-temperature exciton linewidth in short-period superlattices

The power loss of hot two-dimensional excitons in GaAs/AlxGa1-xAs multiple quantum wells and the corresponding energy relaxation times are calculated in the present work. A simplified variational envelope function is assumed for the 1s excitonic level in an infintely deep well and the exciton distribution is described by an effective exciton temperature. For deformation-potential acoustic-phonon scattering, a simple expression for the power loss derived by Takagahara is used, while for polar-optic-phonon scattering the expression is developed in the present paper. The calculated values indicate that for lattice and exciton temperatures below 150 K, polar-optic-phonon scattering contributes little to the power loss. The energy relaxation time due to the acoustic-phonon scattering is found to be about 34 times higher than the experimental estimate and hence the higher-lying states have to be considered to obtain enhanced energy relaxation rate. © 1992 The American Physical Society.

Energy relaxation of hot two-dimensional excitons in a GaAs quantum well by exciton-phonon interaction

We have derived expressions for the linewidth of excitons in a quantum well in the presence of interface roughness scattering, by using the Fermi golden rule and also by introducing the self-consistent Born approximation (SCBA). The fluctuation in the well width is assumed to have a Gaussian autocorrelation and is characterized by a height and a correlation length. The linewidth obtained from the golden rule depends on 2 and changes as L-6 with well width L. The SCBA expression is proportional to, shows a weak dependence on, and varies as L-3. It also agrees with the expression obtained under a statistical-fluctuation model. The calculated results of the linewidth for a GaAs-AlxGa1-xAs quantum well under the golden rule are quite high, while the SCBA results are closer to the experimental data. © 1991 The American Physical Society.

Effect of interface roughness on excitonic linewidth in a quantum well: Golden-rule and self-consistent-Born-approximation calculations

We have calculated the mobility of two-dimensionally free excitons in a quantum well by considering various scattering processes. The relaxation times are derived by using a variational wave function for the 1s exciton in the lowest subband in an infinitely deep well. The calculated mobilities for the GaAs well at first increase with temperature due to the predominance of the interface-roughness scattering, then attain a peak, and finally decrease with temperature as the deformation-potential scattering dominates. The piezoelectric scattering has less importance. The calculated values agree with the experimental data for 8- and 15-nm-wide wells up to about 150 K; however, the disagreement between the values for a 4-nm-wide well indicates that the effect of a finite barrier should be considered. The polar-optic-phonon scattering has been included to explain the rapid decrease of the experimental data above 150 K; however, the single-subband approximation gives too high a value for the mobility, while the values for bulk excitons are quite low compared to the experimental data. © 1991 The American Physical Society.

Calculation of the mobility of two-dimensional excitons in a GaAs/AlxGa1-xAs quantum well

Korean Lawyers Association Journal

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Journal	Applied Physics Letters
Publisher	-
ISSN	0003-6951