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Title: Free electron-driven photophysics in n-type doped silicon nanocrystals

Abstract

Although there have been extensive speculation regarding the applicability of doped silicon nanocrystals (Si NCs) in optoelectronic technologies, a quantitative analysis on the photophysical workings of introduced free carriers remains elusive. Here, we present a comprehensive study on the photophysics of ~7.5 nm heavily phosphorous-doped Si NCs, using a combination of spectroscopic techniques. We correlate the carrier dynamics with the location of the free carriers - which we tune from NC core to surface depending on the state of oxidation. The strength of the Coulomb interactions between the photoexcited electron-hole pairs and the doping-induced free carriers depends on (1) the concentration of free carriers, (2) the location of these carriers, and (3) the diameter of the NCs. In contrast to prior studies, the photoexcited carrier dynamics in these n-type doped Si NCs are dominated by strong Coulomb interactions with doping-induced free electrons, characterized by a negative trion lifetime of around 9 ns. While radiative recombination in doped direct bandgap NCs can often still compete with trion recombination (allowing emission to be present), emission in our doped Si NCs is completely quenched due to the relatively slow radiative recombination in these indirect bandgap NCs. Furthermore, multi-exciton interaction times are slightly shortenedmore » compared to those of intrinsic Si NCs, which we attribute to an increased number of free electrons, enhancing the oscillator strength of Auger recombination. These results constitute a framework for the optimization of doped Si NC synthesis techniques and device engineering directions for future doped-Si NC-based optoelectronic and photovoltaic applications.By making use of multiple spectroscopic techniques we provide a comprehensive understanding of the photophysics of n-type doped Si nanocrystals.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]
  1. National Renewable Energy Laboratory; Golden; USA
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE National Renewable Energy Laboratory (NREL), Laboratory Directed Research and Development (LDRD) Program
OSTI Identifier:
1458906
Report Number(s):
NREL/JA-5900-71012
Journal ID: ISSN 2040-3364; NANOHL
DOE Contract Number:
AC36-08GO28308
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nanoscale; Journal Volume: 10; Journal Issue: 25
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 77 NANOSCIENCE AND NANOTECHNOLOGY; silicon nanocrystals; phosphorus doping; coulomb interactions; ultrafast spectroscopy

Citation Formats

Limpens, R., and Neale, N. R. Free electron-driven photophysics in n-type doped silicon nanocrystals. United States: N. p., 2018. Web. doi:10.1039/C8NR02173B.
Limpens, R., & Neale, N. R. Free electron-driven photophysics in n-type doped silicon nanocrystals. United States. doi:10.1039/C8NR02173B.
Limpens, R., and Neale, N. R. Mon . "Free electron-driven photophysics in n-type doped silicon nanocrystals". United States. doi:10.1039/C8NR02173B.
@article{osti_1458906,
title = {Free electron-driven photophysics in n-type doped silicon nanocrystals},
author = {Limpens, R. and Neale, N. R.},
abstractNote = {Although there have been extensive speculation regarding the applicability of doped silicon nanocrystals (Si NCs) in optoelectronic technologies, a quantitative analysis on the photophysical workings of introduced free carriers remains elusive. Here, we present a comprehensive study on the photophysics of ~7.5 nm heavily phosphorous-doped Si NCs, using a combination of spectroscopic techniques. We correlate the carrier dynamics with the location of the free carriers - which we tune from NC core to surface depending on the state of oxidation. The strength of the Coulomb interactions between the photoexcited electron-hole pairs and the doping-induced free carriers depends on (1) the concentration of free carriers, (2) the location of these carriers, and (3) the diameter of the NCs. In contrast to prior studies, the photoexcited carrier dynamics in these n-type doped Si NCs are dominated by strong Coulomb interactions with doping-induced free electrons, characterized by a negative trion lifetime of around 9 ns. While radiative recombination in doped direct bandgap NCs can often still compete with trion recombination (allowing emission to be present), emission in our doped Si NCs is completely quenched due to the relatively slow radiative recombination in these indirect bandgap NCs. Furthermore, multi-exciton interaction times are slightly shortened compared to those of intrinsic Si NCs, which we attribute to an increased number of free electrons, enhancing the oscillator strength of Auger recombination. These results constitute a framework for the optimization of doped Si NC synthesis techniques and device engineering directions for future doped-Si NC-based optoelectronic and photovoltaic applications.By making use of multiple spectroscopic techniques we provide a comprehensive understanding of the photophysics of n-type doped Si nanocrystals.},
doi = {10.1039/C8NR02173B},
journal = {Nanoscale},
number = 25,
volume = 10,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2018},
month = {Mon Jan 01 00:00:00 EST 2018}
}