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

Journal Article · Thu Apr 14 00:00:00 EDT 2016 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4945993· OSTI ID:22594581

Bose, Sumanta; Zhang, D. H. ^[1]; Song, Zhigang ^[1]

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1. School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore)

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.

• OSTI ID: 22594581
• Journal Information: Journal of Applied Physics, Vol. 119, Issue 14; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
CADMIUM SELENIDES
CADMIUM SULFIDES
CARRIER DENSITY
CURRENT DENSITY
EFFECTIVE MASS
ELECTRONIC STRUCTURE
ELECTRONS
FERMI LEVEL
GAIN
HOLES
L-S COUPLING
MATRIX ELEMENTS
NANOSTRUCTURES
OPACITY
PHOTON EMISSION
PHOTONS
RED SHIFT
THICKNESS
TWO-DIMENSIONAL CALCULATIONS
WAVE FUNCTIONS