L’étude de l’InP et du GaP suite à l’implantation ionique de Mn et à un recuit thermique

This thesis is dedicated to the study of InMnP and GaMnP materials fabricated by ion implantation and thermal annealing.  More precisely we have investigated the possibility of forming by ion implantation homogeneous InMnP and GaMnP materials (alloys), containing up to 5 at. % of Mn, that would be in a ferromagnetic state for possible applications in spintronics.  In the first introductive chapter we give the motivations for this research and briefly comment the literature existent on this subject. The second chapter describes the principles of ion implantation, which is the technique used for the fabrication of the samples.  The effects of the energy, fluency and direction of the ion beam on the implantation profile and the formation of damages will be highlighted.  Also in this chapter we shall find information concerning the semiconducting substrates used for the implantation. The experimental techniques used for the structural, chemical and magnetic characterisation of the samples, together with their limitations are discussed in the third chapter.  Some theoretical principles of magnetism necessary for the understanding of the magnetic measurements are presented in chapter 4. The fifth chapter is dedicated to the study of the morphology and magnetic properties of the substrates used for implantation and the sixth chapter to the study of samples implanted with Mn without thermal annealing.  In particular we’ll see in this chapter that Mn implantation at more then 1016 ions/cm2 makes amorphous the implanted layer and the Mn atoms are distributed in depth following a Gaussian profile.  The implanted Mn atoms are in a paramagnetic state between 5 and 300 K having the spin value of 5/2. In chapter 7 we present the properties of samples annealed at low temperatures. We shall see that in these samples the implanted layer is polycristalline and the Mn atoms are still in a paramagnetic state. In the chapters 8 and 9 that contain most of the results of this thesis, we present the measurements on samples annealed at high temperatures:  in chapter 8 one shall find results on InP and GaP implanted with Mn and in chapter 9 one shall see results on InP co-implanted with Mn and P. Firstly, in chapter 8 we’ll see that thermal annealing at high temperatures leads to an epitaxial recrystallization of InMnP and GaMnP.  But most of the Mn atoms diffuse to the surface due to a segregation effect.  In the regions at the surface, highly concentrated in Mn, the XRD and TEM measurement identify the formation of MnP and In crystalline.  The magnetic measurements identify also the presence of ferromagnetic MnP.   Moreover in these measurements one finds that 60 % of the implanted Mn is in a paramagnetic state with the spin value reduced with respect to that found in un-annealed samples. In the InP samples co-implanted with Mn and P we have only a partial recrystallization but, the effect of segregation of Mn at the surface is much reduced.  In this case more than 50 % of the implanted Mn forms ferromagnetic MnP and the rest of it is diluted in InP, in a paramagnetic state with spin 5/2. Finally, in the last chapter 10 we present the principal conclusion that we have reached and discuss the results and their implications.

Keyphrases: InP, GaP, Mn, MnP, Ion implantation, InP, GaP, Mn, MnP, Segregation