The Local Structure Of The Mn-doped Gan Semiconductor Materials Research

Dilute magnetic semiconductor(DMS) materials are increasingly attracting intense interest as promising candidates for a new generation of multifunctional spintronics devices.In Mn dopedâ…¢-â…¤DMS,Mn minimally substitutes for the groupâ…¢atom and simultaneously provides a localized magnetic moment and a hole, leading to Mn 3d-host sp exchange and ferromagnetic ordering.Among theâ…¢-â…¤DMS,GaAs:Mn has bee studied rigorously for the last few years.Recently,the predictions that GaN:Mn have the higher Curie temperatures(T_C) exceeding room temperature by theoretical calculations on the basis of the mean-field Zener model of ferromagnetism have stimulated more experimental and theoretical studies on this system.In this thesis theâ…¢-â…¤DMS GaN:Mn and GaAs:Mn thin films with different Mn doping density are studied by synchrony radiation method.The local structures of Mn in the doping films are studied by the Mn L-edge X-ray absorption spectroscopy (XAS) measurement and the K-edge extended X-ray absorption fine structure (EXAFS) technique.The structural and vibrate properties of the thin films are studied by X-ray diffraction(XRD) and Raman spectra.The relationship between the nature of Mn,the p-d hybridization and Mn doping density is discussed by comparing with the theoretical calculations.The results show that the Mn doping density has a great effect on the Mn local structures and the p-d hybridization of the Mn and host.Mn occupations in GaN are strongly influenced by the Mn doping concentrations and have different geometry configurations at surfaces or in the bulk.A new structural model of Mn₅ microclusters is proposed for the GaMnN surface,which explains well the L₃ edge XAS experimental results,and is also supported by our total formation energy calculations.The combined analysis of Mn L₃ edge and K edge XAS measurements is applied to identify the different characters of Mn atoms at surface or in bulk and provides a useful method for understanding the local structure of Mn in GaMnN,which greatly depends on sample preparations and is really important for the magnetic properties of DMSs.One the other hand,the local structure around Mn in GaAs:Mn is studied by using Mn K-edge extended X-ray absorption fine structure and near edge X-ray absorption fine structure.It is worth to mention that as simulating experimental curves, a model based on mixture of various possible configurations for Mn atoms has been used to clarify the complex local structures of our samples with different doping density.For 5%Mn doping sample,the secondary phase of MnAs appears and the sample with 8%doping density after the annealed process can form Mn clusters. Therefore,it is imperative to understand the nature of Mn atoms in the host material to get an adequate understanding of the ferromagnetic behavior in DMSs.