Publication detail

Near-field optical measurement of carrier recombination in InAs/GaAs quantum dots

TOMÁNEK, P., DOBIS, P., BENEŠOVÁ, M., GRMELA, L.

Original Title

Near-field optical measurement of carrier recombination in InAs/GaAs quantum dots

Czech Title

Měření rekombinace nábojů v InAs/GaAs kvantových jamách pomocí SNOM

English Title

Near-field optical measurement of carrier recombination in InAs/GaAs quantum dots

Type

abstract

Language

en

Original Abstract

The applicability of scanning near-field scanning optical microscopy (SNOM) for optical characterization of semiconductors with InAs/GaAs quantum dots is discussed. Highly uniform and sharply aligned InAs QDs were grown on metastable In-GaAs/GaAs structures with cross-hatched dislocation patterns induced by thermal annealing. Photoexcited carrier dynamics are studied using time-resolved photoluminescence in the optical near-field. Comparison with randomly distributed InAs quantum dots grown on planar substrates shows that different channels are responsible for recombination of free carriers. In the case of aligned QDs, the PL intensity increases superlinearly with excitation power, a clear indication of the importance of non-radiative recombination. The carrier dynamics can be described by a set of rate equations that model the capture of holes and electrons from inside the QDs to the dislocation-related traps and to the point traps close to the quantum dots. Numerical calculations show excellent agreement with the experimental results for all excitation powers. Then changing the barrier of sample from 5 nm to the 10 nm, only the capture rate for the dislocation related traps changes due to the larger distance between dots and dislocations. For the sample with 20 nm barrier, a higher concentration of traps near the dots is needed to explain the short carrier lifetimes in the dots for this sample. It should be noted that when simulations were performed with just one type of trap, independently of its parameters, no good fit to the experiment could be obtained. The correlation of experimental data and calculation leads us to presume that several of the standard optical characterization methods can be coupled with SNOM to provide higher spatial resolution in the local measurements. The applicability of SNOM as a real-time in-situ probe shares some of the problems of other proximal probe methods, but offers enough new capabilities to warrant its application.

Czech abstract

V článku je diskutována použitelnost SNOM pro charakterizaci polovodičů s InAs/GaAs kvantovými jámami. Vysoce uniformní ostře seřazené jámy vyrostly na metastabilních In-GaAs/GaAs strukturách s dislokacemi indukovanými teplotním žíháním. Dynamika fotoexcitovaných nábojů je zkoumána pomocí fotoluminiscence s časovým rozlišením v optickém blízkém poli. Porovnání s náhodně rozloženými InAs kvantovými jámamai na planárním povrchu ukazuje, že různé kanály jsou zodpovědné za rekombinaci volných nosičů. V případně seřazených QD, vzrůsté PL intenzita s energií excitace, což jasně ukazuje na význam nezářivé rekombinace. Dynamika nosičů může být popsána systéme poměrových rovnic, které modelují zachycení elektronů a děr z hloubi QD do pastí na dislokacích a do bodových pastí v blízkosti jámy. Výpočet ukazuje shodu s experimentálním výsledky pro různé excitační energie. Změnou bariéry z 5 nm na 10 nm se mění poměr zachycení pouze pro dislokační pasti, což je způsobeno velkou vzdáleností mezi jámami a dislokacemi. Pro vzorek s 20 nm bariérou je třeba vyšší koncentrace pastí v blízkosti jam k tomu, aby se vysvětlily kratší živostnosti nábojů v jamách vzorku. Jsou-li simulace provedeny pouze s jedním typem pastí, nazávisle na jejích parametrech, není možné dostat shodu s experimentem. Korelace experimentálních dat s výpočetem vede k předpokladu, že některé z SNOM charakterizačních technik mohou být použity k dosažení vyšší rozlišovací schopnosti. Použitelnost SNOM jako in-situ sondy v reálném čase vykazuje stejný typ problémů jako u ostatních sondových metod, ale nabízí i některé zajímavé kapcity v měření.

English abstract

The applicability of scanning near-field scanning optical microscopy (SNOM) for optical characterization of semiconductors with InAs/GaAs quantum dots is discussed. Highly uniform and sharply aligned InAs QDs were grown on metastable In-GaAs/GaAs structures with cross-hatched dislocation patterns induced by thermal annealing. Photoexcited carrier dynamics are studied using time-resolved photoluminescence in the optical near-field. Comparison with randomly distributed InAs quantum dots grown on planar substrates shows that different channels are responsible for recombination of free carriers. In the case of aligned QDs, the PL intensity increases superlinearly with excitation power, a clear indication of the importance of non-radiative recombination. The carrier dynamics can be described by a set of rate equations that model the capture of holes and electrons from inside the QDs to the dislocation-related traps and to the point traps close to the quantum dots. Numerical calculations show excellent agreement with the experimental results for all excitation powers. Then changing the barrier of sample from 5 nm to the 10 nm, only the capture rate for the dislocation related traps changes due to the larger distance between dots and dislocations. For the sample with 20 nm barrier, a higher concentration of traps near the dots is needed to explain the short carrier lifetimes in the dots for this sample. It should be noted that when simulations were performed with just one type of trap, independently of its parameters, no good fit to the experiment could be obtained. The correlation of experimental data and calculation leads us to presume that several of the standard optical characterization methods can be coupled with SNOM to provide higher spatial resolution in the local measurements. The applicability of SNOM as a real-time in-situ probe shares some of the problems of other proximal probe methods, but offers enough new capabilities to warrant its application.

Keywords

quantum dot, near-field optics, local spectroscopy, carrier recombination

Released

23.06.2004

Publisher

Vutium, Brno

Location

Brno

ISBN

80-214-26732-X

Book

Material structure & micromechanics of fracture

Pages from

115

Pages to

115

Pages count

1

BibTex


@misc{BUT59955,
  author="Pavel {Tománek} and Pavel {Dobis} and Markéta {Benešová} and Lubomír {Grmela}",
  title="Near-field optical measurement of carrier recombination in InAs/GaAs quantum dots",
  annote="The applicability of scanning near-field scanning optical microscopy (SNOM) for optical characterization of semiconductors with InAs/GaAs quantum dots is discussed. 
Highly uniform and sharply aligned InAs QDs were grown on metastable In-GaAs/GaAs structures with cross-hatched dislocation patterns induced by thermal annealing. Photoexcited carrier dynamics are studied using time-resolved photoluminescence in the optical near-field. Comparison with randomly distributed  InAs quantum dots grown on planar substrates shows that different channels are responsible for recombination of free carriers. In the case of aligned QDs, the PL intensity increases superlinearly with excitation power, a clear indication of the importance of non-radiative recombination. 
The carrier dynamics can be described by a set of rate equations that model the capture of holes and electrons from inside the QDs to the dislocation-related traps and to the point traps close to the quantum dots. Numerical calculations show excellent agreement with the experimental results for all excitation powers. Then changing the barrier of sample from 5 nm to the 10 nm, only the capture rate for the dislocation related traps changes due to the larger distance between dots and dislocations. For the sample with 20 nm barrier, a higher concentration of traps near the dots is needed to explain the short carrier lifetimes in the dots for this sample. It should be noted that when simulations were performed with just one type of trap, independently of its parameters, no good fit to the experiment could be obtained.

The correlation of experimental data and calculation leads us to presume that several of the standard optical characterization methods can be coupled with SNOM to provide higher spatial resolution in the local measurements. The applicability of SNOM as a real-time in-situ probe shares some of the problems of other proximal probe methods, but offers enough new capabilities to warrant its application.
",
  address="Vutium, Brno",
  booktitle="Material structure & micromechanics of fracture",
  chapter="59955",
  institution="Vutium, Brno",
  year="2004",
  month="june",
  pages="115",
  publisher="Vutium, Brno",
  type="abstract"
}