Epitaxie de nouvelles hétérostructures pour la filière GaAs : puits/boîtes quantiques GaInAs sur surfaces structurées et alliages GaAsBi

Une des forces des semi-conducteurs composés et de leurs alliages est de permettre une ingénierie très flexible des structures de bande et de couvrir une large bande spectrale intéressant de nombreuses applications optoélectroniques. De plus, il est possible de les réaliser sous forme de puits et boîtes quantiques, qui constituent des émetteurs efficaces pour les diodes laser. Mes travaux de thèse s'inscrivent dans le contexte du développement de nouvelles hétérostructures quantiques pour la filière GaAs en vue d'étendre sa gamme d'application. En premier lieu, la reprise d'épitaxie par jet moléculaire des puits quantiques de GaInAs et la croissance dirigée des boites quantiques d'InAs sur des surfaces nanostructurées de GaAs ont été visées. La structuration de surface a été réalisée par un procédé de nanoimpression que nous avons mis au point et par lithographie électronique. La désoxydation in situ par plasma hydrogène et sous flux de gallium a été étudiée et des surfaces lisses et propres ont été obtenues. L'influence de l'orientation et de la dimension des motifs sur les nanostructures a été précisée. La luminescence des nanostructures à température ambiante a été démontrée. En second lieu, la croissance des puits quantiques de GaAsBi a été développée après une optimisation des conditions de croissance de couches épaisses de GaAsBi. Une émission à température ambiante d'une longueur d'onde de 1.22 µm a été mesurée pour un puits contenant 7% de bismuth. Il présente des interfaces planes, une épaisseur uniforme et est déformé élastiquement. Par ailleurs, la présence d'états localisés a été mise en évidence par spectroscopie de photoluminescence. Nous avons montré que les recuits ne parviennent pas à guérir ces défauts.Compound semiconductors provide a high flexibility in band structure engineering and cover a wide spectral band, meeting requirements for a large amount of optoelectronic applications. Moreover, they can be structured as quantum wells or quantum dots to form efficient emitters for laser diodes. My thesis deals with the development of novel quantum heterostructures for GaAs technology with the aim to further extend this material system range of applications. I have investigated two kinds of nanostructures: growth on nanostructured surfaces and GaAsBi alloys. The first part of the work is dedicated to the molecular beam epitaxy of InGaAs quantum wells and InAs quantum dots on nanopatterned GaAs surfaces. Surface patterning was carried out using a nanoimprint lithography process that we have developed and by electron beam lithography. Critical to the success of the subsequent growth step was the development and optimisation of hydrogen plasma and Ga-triggered oxide desorption from patterned GaAs to obtain smooth and clean surfaces. Our results show that growth of quantum dots can be directed, with dependence in orientation and pattern size. Furthermore, photoluminescence from these nanostructures is observed at room temperature. In the second part of the thesis, the growth of GaAsBi quantum wells was studied after optimization of the growth conditions for thick GaAsBi layers. Room temperature emission up to a wavelength of 1.22 µm is demonstrated for a strained GaAsBi quantum well (7% Bi). This latter structure exhibits flat interfaces. Moreover, the presence of defect-related localized states was highlighted by photoluminescence spectroscopy. It is further shown that these defects cannot be entirely suppressed by a rapid thermal annealing treatment

GaSbBi alloys and heterostructures: fabrication and properties

International audienceDilute bismuth (Bi) III-V alloys have recently attracted great attention, due to their properties of band-gap reduction and spin-orbit splitting. The incorporation of Bi into antimonide based III-V semiconductors is very attractive for the development of new optoelectronic devices working in the mid-infrared range (2-5 µm). However, due to its large size, Bi does not readily incorporate into III-V alloys and the epitaxy of III-V dilute bismides is thus very challenging. This book chapter presents the most recent developments in the epitaxy and characterization of GaSbBi alloys and heterostructures

Epitaxie de nouvelles hétérostructures pour la filière GaAs : puits/boîtes quantiques GaInAs sur surfaces structurées et alliages GaAsBi

Compound semiconductors provide a high flexibility in band structure engineering and cover a wide spectral band, meeting requirements for a large amount of optoelectronic applications. Moreover, they can be structured as quantum wells or quantum dots to form efficient emitters for laser diodes. My thesis deals with the development of novel quantum heterostructures for GaAs technology with the aim to further extend this material system range of applications. I have investigated two kinds of nanostructures: growth on nanostructured surfaces and GaAsBi alloys. The first part of the work is dedicated to the molecular beam epitaxy of InGaAs quantum wells and InAs quantum dots on nanopatterned GaAs surfaces. Surface patterning was carried out using a nanoimprint lithography process that we have developed and by electron beam lithography. Critical to the success of the subsequent growth step was the development and optimisation of hydrogen plasma and Ga-triggered oxide desorption from patterned GaAs to obtain smooth and clean surfaces. Our results show that growth of quantum dots can be directed, with dependence in orientation and pattern size. Furthermore, photoluminescence from these nanostructures is observed at room temperature. In the second part of the thesis, the growth of GaAsBi quantum wells was studied after optimization of the growth conditions for thick GaAsBi layers. Room temperature emission up to a wavelength of 1.22 μm is demonstrated for a strained GaAsBi quantum well (7% Bi). This latter structure exhibits flat interfaces. Moreover, the presence of defect-related localized states was highlighted by photoluminescence spectroscopy. It is further shown that these defects cannot be entirely suppressed by a rapid thermal annealing treatment.Une des forces des semi-conducteurs composés et de leurs alliages est de permettre une ingénierie très flexible des structures de bande et de couvrir une large bande spectrale intéressant de nombreuses applications optoélectroniques. De plus, il est possible de les réaliser sous forme de puits et boîtes quantiques, qui constituent des émetteurs efficaces pour les diodes laser. Mes travaux de thèse s'inscrivent dans le contexte du développement de nouvelles hétérostructures quantiques pour la filière GaAs en vue d'étendre sa gamme d'application. En premier lieu, la reprise d'épitaxie par jet moléculaire des puits quantiques de GaInAs et la croissance dirigée des boites quantiques d'InAs sur des surfaces nanostructurées de GaAs ont été visées. La structuration de surface a été réalisée par un procédé de nanoimpression que nous avons mis au point et par lithographie électronique. La désoxydation in situ par plasma hydrogène et sous flux de gallium a été étudiée et des surfaces lisses et propres ont été obtenues. L'influence de l'orientation et de la dimension des motifs sur les nanostructures a été précisée. La luminescence des nanostructures à température ambiante a été démontrée. En second lieu, la croissance des puits quantiques de GaAsBi a été développée après une optimisation des conditions de croissance de couches épaisses de GaAsBi. Une émission à température ambiante d'une longueur d'onde de 1.22 μm a été mesurée pour un puits contenant 7% de bismuth. Il présente des interfaces planes, une épaisseur uniforme et est déformé élastiquement. Par ailleurs, la présence d'états localisés a été mise en évidence par spectroscopie de photoluminescence. Nous avons montré que les recuits ne parviennent pas à guérir ces défauts

Épitaxie de nouvelles hétérostructures pour la filière GaAs (puits-boîtes quantiques GaInAs sur surfaces structurées et alliages GaAsBi)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Contactless conductivity measurement for ITO nanolayers on AsGa substrats over a wide frequency range

International audienceWe report on the application of a new contactless method based on eddy currents with a view to characterizing some transport properties of a large range of semiconductors. The innovative approach of this work consists in measuring the impedance of the coil by reflectometry using a broadband multicarrier test signal. The device works well with silicon wafers with a constant conductivity over a wide frequency range. Because of their electrical conductivity and high optical transmittance in the visible and near-IR regions of electromagnetic spectrum, indium tin oxide (ITO) films have motivated great interests in experimental studies and technological applications. The estimation of their electrical conductivity is a key point to develop these devices. On this paper we show that the setup can be used for the frequency characterization of ITO and AsGa nanolayers wich exhibit a frequency dependent behavior. The low frequency measurement are found in agreement with the classical four point probe setup

Photoluminescence from InGaAs/GaAs quantum well regrown on a buried patterned oxidized AlAs layer

International audienceWe present a quasi-planar technological approach for forming a flexible and versatile confinement scheme based on oxidation of AlGaAs buried layers combined to an epitaxial regrowth. This method improves the electrical and optical confinements compared to the lateral oxidation since it allows to define confinement areas from a planar surface. This technique is suitable for the realization of advanced integrated photonic components arrays with close device-to-device spacing such as two-dimensional arrays of vertical-cavity surface-emitting lasers. Our results prove that the oxidation and epitaxial regrowth can be sequenced in a process flow, leading to viable confinement while preserving good radiative properties

Influence of chemical process on structural and optical properties of as-grown and thermal annealed GaAsBi alloys

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Thermal annealing effects on optical and structural properties of GaBiAs epilayers: Origin of the thermal annealing-induced redshift in GaBiAs

We report on an investigation of optical and structural properties of as-grown and thermal annealed GaBixAs1-x (x = 0.012, 0.018 and 0.03) epilayers by photomodulated reflectance (PR) spectroscopy, atomic force microscopy (AFM) and micro-Raman spectroscopy. PR spectra are analyzed by third derivative functional form (TDFF) lineshape. Optical transition energies are calculated using strain-included valence band anticrossing (VBAC) model. According to the results, optical transitions are from conduction bandedge to heavy hole bandedge and to light hole bandedge, which are affected by compressive strain and effect of strain is clearly seen when Bi concentration exceeds 2%. We also determine the band-anticrossing interaction parameter C-BiM as 1.33 eV. TDFF analysis of as-grown and thermal annealed samples reveal that thermal annealing causes an unexpectedly large redshift of -22 meV/Bi% in the bandgap that corresponds to the increase of Bi composition by -25% in the GaAs lattice. The origin of this redshift is analyzed by AFM and Raman spectroscopy. Surface morphology of the GaBiAs samples show that droplets appear on the GaBiAs surface and their sizes increase with increasing Bi concentration, but tend to decrease following thermal annealing process and some surface droplets leave pits in their locations. Raman spectroscopy and AFM results give hints of diffusion of some Bi atoms from surface into the epilayer that causes an increase in Bi concentration of the alloy. This increase explains the observed annealing-induced redshift of the bandgap in PR measurement. (C) 2016 Elsevier B.V. All rights reserved

Thermal annealing effects on optical and structural properties of GaBiAs epilayers: Origin of the thermal annealing-induced redshift in GaBiAs

International audienceWe report on an investigation of optical and structural properties of as-grown and thermal annealed GaBixAs1−x (x = 0.012, 0.018 and 0.03) epilayers by photomodulated reflectance (PR) spectroscopy, atomic force microscopy (AFM) and micro-Raman spectroscopy. PR spectra are analyzed by third derivative functional form (TDFF) lineshape. Optical transition energies are calculated using strain-included valence band anticrossing (VBAC) model. According to the results, optical transitions are from conduction bandedge to heavy hole bandedge and to light hole bandedge, which are affected by compressive strain and effect of strain is clearly seen when Bi concentration exceeds 2%. We also determine the band-anticrossing interaction parameter CBiM as 1.33 eV. TDFF analysis of as-grown and thermal annealed samples reveal that thermal annealing causes an unexpectedly large redshift of ∼22 meV/Bi% in the bandgap that corresponds to the increase of Bi composition by ∼25% in the GaAs lattice. The origin of this redshift is analyzed by AFM and Raman spectroscopy. Surface morphology of the GaBiAs samples show that droplets appear on the GaBiAs surface and their sizes increase with increasing Bi concentration, but tend to decrease following thermal annealing process and some surface droplets leave pits in their locations. Raman spectroscopy and AFM results give hints of diffusion of some Bi atoms from surface into the epilayer that causes an increase in Bi concentration of the alloy. This increase explains the observed annealing-induced redshift of the bandgap in PR measurement