The Structural and Magnetic Properties of MnP Films and Nanocrystals

Les semi-conducteurs magnétiques hétérogènes constitués de nano-aimants de pnictures de manganèse incorporés dans des matrices de semi-conducteurs ont des applications magnéto- électroniques et magnéto-optoélectroniques potentielles tel que la magnétorésistance géante et les effets magnétooptiques géants en raison de leurs fonctionnalités magnétiques. Parmi ces matériaux, les systèmes hétérogènes avec des températures de Curie élevées, comme MnSb, MnAs et MnP, ont fait l'objet de nombreuses études. Étant donné que la texture des nanoagrégats affecte fortement les fonctionnalités magnétiques des semi-conducteurs hétérogènes, nous devons avoir un contrôle sur la structure et la texture du système afin de réaliser les fonctions magnétiques souhaitées. Par conséquent, il est nécessaire de comprendre les propriétés de l'hétérostructure en fonction de sa structure. Les nanoparticules de MnP ferromagnétiques encastrées dans une matrice de phosphure de gallium (GaP), GaP:MnP, crues par épitaxie en phase vapeur (MOVPE) ont été étudiées comme un système modèle pour vérifier à quel niveau la texture pouvait être pré-conditionnée par synthèse. Malgré les études détaillées sur la façon dont certains éléments structuraux (par exemple la taille des nanoparticules) peuvent être contrôlés par les paramètres de croissance(par exemple la température de croissance), la complexité de ces systèmes n'a pas permis de résoudre cette dépendance. L'objectif général de ce travail est de comprendre le mécanisme de la croissance, de sélection de la texture du MnP dans le GaP et comment la texture pourrait être conditionnée par les paramètres de croissance. Pour atteindre notre objectif, nous avons choisi d'étudier un système moins complexe, des couches minces de MnP crues sur substrat de GaP, afin d'approfondir notre compréhension du mécanisme de croissance et d'évolution de la texture des hétérostructures. La comparaison de l'évolution de la texture de couches minces et de celle des hétérostructures nous aide à comprendre le rôle de la matrice de GaP, ce qui pourrait conduire à la conception de structures avec les propriétés souhaitées. Un autre objectif de ce travail est de développer une méthode simple pour déterminer la taille magnétique des nanoparticules de MnP ainsi que leur distribution. Puisque notre sujet d'intérêt porte sur la texture et la structure magnétique des nanoparticules, la taille magnétique, par opposition à la taille physique, des nanoparticules est la composante structurale pertinente à étudier. Il n'existe pas dans la littérature de modèle cohérent pour déterminer la distribution de la taille d'un ensemble de nanoparticules dont certaines sont superparamagnétiques et d'autres ferromagnétiques, tel que les nanoparticules de MnP dans le GaP.----------Abstract Heterogeneous magnetic semiconductors consisting manganese pnictide nanomagnets embedded in semiconductor matrices have potential magnetoelectronic and magnetooptoelectronic applications due to their enhanced magnetic functionalities, such as Giant Magneto- Resistance (GMR) and Giant Magneto-Optical (GMO) Kerr and Faraday eects. Among these, heterogeneous systems with higher Curie temperatures, such as manganese antimonide, manganese arsenide, and manganese phosphide (MnP) have been the focus of many studies. Since the texture of the nanoclusters highly aects the magnetic functionalities of the heterogeneous semiconductors, in order to achieve the desired magnetic functionalities we need to have a control over the structure and texture of the system. Hence, it is necessary to understand the properties of the heterostructure in relation to its structure. Ferromagnetic MnP nanoclusters embedded in gallium phosphide (GaP) matrix, GaP:MnP, grown by Metal-Organic Vapor Phase Epitaxy (MOVPE) has been studied as a model system to verify to what level the texture could be pre-conditioned by synthesis. Despite the valuable achievements of the studies on how some structural components (e.g. size of nanoclusters) can be controlled by growth parameters (e.g. growth temperature), the complexity of the structure did not allow to fully exploit this matter. The general objective of this work is to understand the growth mechanism and texture selection of MnP on GaP and how the texture could be pre-conditioned by growth. To achieve our goal we chose to study a less complex system, MnP thin lms grown on GaP, in order to expand the limits of our understanding on the growth mechanism and texture evolution of the heterostructure systems. Comparing the texture evolution of thin lms and heterostructures helps us understand the role of the surrounding GaP matrix on texture, which may potentially lead to designing structures with desired properties. Another objective of this work is to develop a simple method to determine the magnetic size distribution and magnetic size of MnP nanoclusters. Since our topic of interest deals with the texture and structure of magnetic nanoparticles, the magnetic size of the nanoparticles is the relevant structural component to study, rather than their apparent physical size. However, there is a lack of a consistent model to determine the magnetic size distribution of an assembly of superparamagnetic and ferromagnetic nanoparticles (such as MnP nanoclusters in GaP:MnP) in the literature. To analyze the texture of MnP lms we have used X-ray diraction (XRD) and electron microscopy (EM) techniques. We have shown that combining the XRD pole gures and electron diraction patterns obtained from EM makes a much stronger tool to analyze the texture compared to each of the techniques applied alone. Studying the growth time and temperature evolution of th

Growth and luminescence of polytypic InP on epitaxial graphene

Van der Waals epitaxy is an attractive alternative to direct heteroepitaxy where the forced coherency at the interface cannot sustain large differences in lattice parameters and thermal expansion coefficients between the substrate and the epilayer. Herein, the growth of monocrystalline InP on Ge and SiO2/Si substrates using graphene as an interfacial layer is demonstrated. Micrometer‐sized InP crystals are found to grow with interfaces of high crystalline quality and with different degrees of coalescence depending on the growth conditions. Some InP crystals exhibit a polytypic structure, consisting of alternating zinc‐blende and wurtzite phases, forming a type‐II homojunction with well (barrier) width of about 10 nm. The optical properties, investigated using room temperature nano‐cathodoluminescence, indicate the signatures of the direct optical transitions at 1.34 eV across the gap of the zinc‐blende phase and the indirect transitions at ≈1.31 eV originating from the alternating zinc‐blende and wurtzite phases. Additionally, the InP nanorods, found growing mainly on the graphene/SiO2/Si substrate, show optical transition across the gap of the wurtzite phase at ≈1.42 eV. This demonstration of InP growth on graphene and the correlative study between the structure and optical properties pave the way to develop hybrid structures for potential applications in integrated photonic and optoelectronic devices.J.A. and M.d.l.M. acknowledge funding from the Generalitat de Catalunya 2014 SGR 1638 and the Spanish MINECO project e‐TNT (MAT2014‐59961‐C2‐2‐R). ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV‐2013‐0295). O.M. acknowledges support from the NSERC‐Canada (Discovery Grants and Strategic Partnership Grants), the Canada Foundation for Innovation, the MRIF Québec (Coopération Québec‐Catalogne), and the Canada Research Chair. R.M.J. and M.S.A. acknowledges the support by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award # DE‐SC0016007. P.D. and R.M. acknowledge financial support from the NSERC.Peer reviewe

Growth and luminescence of polytypic InP on epitaxial graphene

Van der Waals epitaxy is an attractive alternative to direct heteroepitaxy where the forced coherency at the interface cannot sustain large differences in lattice parameters and thermal expansion coefficients between the substrate and the epilayer. Herein, the growth of monocrystalline InP on Ge and SiO/Si substrates using graphene as an interfacial layer is demonstrated. Micrometer-sized InP crystals are found to grow with interfaces of high crystalline quality and with different degrees of coalescence depending on the growth conditions. Some InP crystals exhibit a polytypic structure, consisting of alternating zinc-blende and wurtzite phases, forming a type-II homojunction with well (barrier) width of about 10 nm. The optical properties, investigated using room temperature nano-cathodoluminescence, indicate the signatures of the direct optical transitions at 1.34 eV across the gap of the zinc-blende phase and the indirect transitions at ≈1.31 eV originating from the alternating zinc-blende and wurtzite phases. Additionally, the InP nanorods, found growing mainly on the graphene/SiO/Si substrate, show optical transition across the gap of the wurtzite phase at ≈1.42 eV. This demonstration of InP growth on graphene and the correlative study between the structure and optical properties pave the way to develop hybrid structures for potential applications in integrated photonic and optoelectronic devices

Growth and Luminescence of Polytypic InP on Epitaxial Graphene

Van der Waals epitaxy is an attractive alternative to direct heteroepitaxy where the forced coherency at the interface cannot sustain large differences in lattice parameters and thermal expansion coefficients between the substrate and the epilayer. Herein, the growth of monocrystalline InP on Ge and SiO/Si substrates using graphene as an interfacial layer is demonstrated. Micrometer-sized InP crystals are found to grow with interfaces of high crystalline quality and with different degrees of coalescence depending on the growth conditions. Some InP crystals exhibit a polytypic structure, consisting of alternating zinc-blende and wurtzite phases, forming a type-II homojunction with well (barrier) width of about 10 nm. The optical properties, investigated using room temperature nano-cathodoluminescence, indicate the signatures of the direct optical transitions at 1.34 eV across the gap of the zinc-blende phase and the indirect transitions at ≈1.31 eV originating from the alternating zinc-blende and wurtzite phases. Additionally, the InP nanorods, found growing mainly on the graphene/SiO/Si substrate, show optical transition across the gap of the wurtzite phase at ≈1.42 eV. This demonstration of InP growth on graphene and the correlative study between the structure and optical properties pave the way to develop hybrid structures for potential applications in integrated photonic and optoelectronic devices