Creation of GaMnAs ferromagnetic semiconductor by combined laser method

Abstract

GaMnAs layers made by pulsed laser deposition in vacuum on semi-insulating GaAs substrates have been studied. During the creation of the structures, the substrate temperature varied in the range from 200 to 350oC, and the thickness of the layers was ~ 50 nm. Samples of the manufactured structures were annealed by pulses of an excimer KrF-laser. The analysis of the Raman scattering spectra of annealed samples using their approximation by Lorentz functions showed, in addition to peaks in the LO- and TO-GaAs modes, the presence of a coupled phonon-plasmon mode. As a result of annealing, a significant increase in the hole conductivity of the layers is observed (the resistance decreases from Rs~107-109 Ω to Rs~ 900-3000 Ω). The type of magnetic field dependence of magnetization at room temperature changes significantly: there is a transition from a nonlinear characteristic with a hysteresis loop for the initial sample (appearing due to the presence of MnAs compound inclusions with a Curie temperature above room temperature) to a linear behavior for the annealed sample. The study of galvanomagnetic properties at temperatures from 10 to 150 K shows the existence of ferromagnetism in GaMnAs layers with a Curie temperature reaching 90 K. The observed effects allow us to conclude that the applied pulsed laser action leads to modification (dissolution) of MnAs inclusions, electrical activation of Mn and, as a consequence, to the formation of a single-phase ferromagnetic semiconductor GaMnAs. Keywords:: pulsed laser deposition, pulsed laser annealing, ferromagnetic semiconductor.