Effect of lateral size and thickness on the electronic structure and optical properties of quasi two-dimensional CdSe and CdS nanoplatelets

The effect of lateral size and vertical thickness of CdSe and CdS nanoplatelets (NPLs) on their electronic structure and optical properties are investigated using an effective-mass envelope function theory based on the 8-band k ⋅ p model with valence force field considerations. Volumetrically larger...

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Main Authors: Bose, Sumanta, Song, Zhigang, Fan, Wei Jun, Zhang, Dao Hua
Other Authors: School of Electrical and Electronic Engineering
Format: Article
Language:English
Published: 2017
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Online Access:https://hdl.handle.net/10356/83586
http://hdl.handle.net/10220/42689
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spelling sg-ntu-dr.10356-835862020-03-07T13:57:26Z Effect of lateral size and thickness on the electronic structure and optical properties of quasi two-dimensional CdSe and CdS nanoplatelets Bose, Sumanta Song, Zhigang Fan, Wei Jun Zhang, Dao Hua School of Electrical and Electronic Engineering Centre for OptoElectronics and Biophotonics II-VI semiconductors Carrier density The effect of lateral size and vertical thickness of CdSe and CdS nanoplatelets (NPLs) on their electronic structure and optical properties are investigated using an effective-mass envelope function theory based on the 8-band k ⋅ p model with valence force field considerations. Volumetrically larger NPLs have lower photon emission energy due to limited quantum confinement, but a greater transition matrix element (TME) due to larger electron-hole wavefunction overlap. The optical gain characteristics depend on several factors such as TME, Fermi factor, carrier density, NPL dimensions, material composition, and dephasing rate. There is a red shift in the peak position, more so with an increase in thickness than lateral size. For an increasing carrier density, the gain spectrum undergoes a slight blue shift due to band filling effect. For a fixed carrier density, the Fermi factor is higher for volumetrically larger NPLs and so is the difference between the quasi-Fermi level separation and the effective bandgap. The transparency injection carrier density (and thus input current density threshold) is dimension dependent and falls for volumetrically larger NPLs, as they can attain the requisite exciton count for transparency with a relatively lower density. Between CdSe and CdS, CdSe has lower emission energy due to smaller bandgap, but a higher TME due to lower effective mass. CdS, however, has a higher so hole contribution due to a lower spin-orbit splitting energy. Both CdSe and CdS NPLs are suitable candidates for short-wavelength LEDs and lasers in the visible spectrum, but CdSe is expected to exhibit better optical performance. MOE (Min. of Education, S’pore) Published version 2017-06-14T02:55:34Z 2019-12-06T15:26:11Z 2017-06-14T02:55:34Z 2019-12-06T15:26:11Z 2016 Journal Article Bose, S., Song, Z., Fan, W. J., & Zhang, D. H. (2016). Effect of lateral size and thickness on the electronic structure and optical properties of quasi two-dimensional CdSe and CdS nanoplatelets. Journal of Applied Physics, 119(14), 143107-. 0021-8979 https://hdl.handle.net/10356/83586 http://hdl.handle.net/10220/42689 10.1063/1.4945993 en Journal of Applied Physics © 2016 American Institute of Physics (AIP). This paper was published in Journal of Applied Physics and is made available as an electronic reprint (preprint) with permission of American Institute of Physics (AIP). The published version is available at: [http://dx.doi.org/10.1063/1.4945993]. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper is prohibited and is subject to penalties under law. 11 p. application/pdf
institution Nanyang Technological University
building NTU Library
country Singapore
collection DR-NTU
language English
topic II-VI semiconductors
Carrier density
spellingShingle II-VI semiconductors
Carrier density
Bose, Sumanta
Song, Zhigang
Fan, Wei Jun
Zhang, Dao Hua
Effect of lateral size and thickness on the electronic structure and optical properties of quasi two-dimensional CdSe and CdS nanoplatelets
description The effect of lateral size and vertical thickness of CdSe and CdS nanoplatelets (NPLs) on their electronic structure and optical properties are investigated using an effective-mass envelope function theory based on the 8-band k ⋅ p model with valence force field considerations. Volumetrically larger NPLs have lower photon emission energy due to limited quantum confinement, but a greater transition matrix element (TME) due to larger electron-hole wavefunction overlap. The optical gain characteristics depend on several factors such as TME, Fermi factor, carrier density, NPL dimensions, material composition, and dephasing rate. There is a red shift in the peak position, more so with an increase in thickness than lateral size. For an increasing carrier density, the gain spectrum undergoes a slight blue shift due to band filling effect. For a fixed carrier density, the Fermi factor is higher for volumetrically larger NPLs and so is the difference between the quasi-Fermi level separation and the effective bandgap. The transparency injection carrier density (and thus input current density threshold) is dimension dependent and falls for volumetrically larger NPLs, as they can attain the requisite exciton count for transparency with a relatively lower density. Between CdSe and CdS, CdSe has lower emission energy due to smaller bandgap, but a higher TME due to lower effective mass. CdS, however, has a higher so hole contribution due to a lower spin-orbit splitting energy. Both CdSe and CdS NPLs are suitable candidates for short-wavelength LEDs and lasers in the visible spectrum, but CdSe is expected to exhibit better optical performance.
author2 School of Electrical and Electronic Engineering
author_facet School of Electrical and Electronic Engineering
Bose, Sumanta
Song, Zhigang
Fan, Wei Jun
Zhang, Dao Hua
format Article
author Bose, Sumanta
Song, Zhigang
Fan, Wei Jun
Zhang, Dao Hua
author_sort Bose, Sumanta
title Effect of lateral size and thickness on the electronic structure and optical properties of quasi two-dimensional CdSe and CdS nanoplatelets
title_short Effect of lateral size and thickness on the electronic structure and optical properties of quasi two-dimensional CdSe and CdS nanoplatelets
title_full Effect of lateral size and thickness on the electronic structure and optical properties of quasi two-dimensional CdSe and CdS nanoplatelets
title_fullStr Effect of lateral size and thickness on the electronic structure and optical properties of quasi two-dimensional CdSe and CdS nanoplatelets
title_full_unstemmed Effect of lateral size and thickness on the electronic structure and optical properties of quasi two-dimensional CdSe and CdS nanoplatelets
title_sort effect of lateral size and thickness on the electronic structure and optical properties of quasi two-dimensional cdse and cds nanoplatelets
publishDate 2017
url https://hdl.handle.net/10356/83586
http://hdl.handle.net/10220/42689
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