Annealing Induced Modifications in (GaMn)As: Electron Spectroscopic Studies
Licentiate thesis, 2010
By incorporating magnetism into semiconductors, it may possibly be viable to enhance the functionality of materials. An exceptionally appealing material in this context is GaAs, which can be doped with Mn atoms. (GaMn)As has fascinated research community as a promising candidate for spintronic application. It is quite appealing due to both its compatibility with existing III-V technology and great progress in improving its magnetic properties. Being fabricated by low temperature molecular beam epitaxy (LT-MBE), due to thermal instability at elevated temperatures, the material contains a high density of various defects compensating Mn acceptors. It is a well-established fact that the ferromagnetic state of (GaMn)As can be stabilized via post growth annealing. Nevertheless, in general, the annealed (GaMn)As layers do not remain useful for further epitaxial overgrowth that might be
included in multilayer structure. In order to overcome this practical difficulty a procedure was devised in which annealing is carried out under amorphous As. The focus of the present thesis is to study the MBE grown (GaMn)As layers annealed under As capping using synchrotron based spectroscopy. The formation of epitaxial MnAs with a 1x2 reconstruction resulting from the reaction between out-diffusing Mn interstitials and As capping has been reported analysing the As3d core levels. The use of topmost MnAs layer of (GaMn)As annealed under As capping has also been described for depositing successive layers of Bi and Mn resulting in formation of uniform surface layers. Moreover Mn2p emission from annealed and as-grown (GaMn)As layers with varying GaAs overlayer thickness has been examined to describe the thickness dependent mechanism that stops the diffusing of interstitial Mn from reaching the surface.