INELASTIC LIGHT SCATTERING STUDY OF DILUTED MAGNETIC SEMICONDUCTORS (SPIN-FLIP, PHONON, RAMAN).

摘要

We have investigated Raman scattering associated with the excitations of the Mn('2+) 3d electrons in diluted magnetic semiconductors in an applied magnetic field. A sharp Raman line due to the spin-flip of the 3d electrons, corresponding to the (DELTA)m(,s) = (+OR-)1 transition, occurs in the paramagnetic phase. Close to band gap resonance, this transition in combination with the zone center LO phonons as well as the (DELTA)m(,s) = (+OR-)2 transitions are present. This resonance suggests a new Raman mechanism involving interband transitions in conjunction with the exchange interaction between band electrons and Mn('2+), and was explored in more detail in magnetic field tuned resonant Raman scattering involving the large magnetic field induced exciton splitting. In the low temperature magnetic phase, the magnon feature of Cd(,1-X)Mn(,X)Te splits into two components in the presence of an applied magnetic field. As the temperature is lowered, the Mn('2+) spin-flip of the paramagnetic phase evolves into the higher energy component of the magnon.('); A spin-flip Raman scattering study of electrons bound to shallow donors was carried out in the diluted magnetic semiconductors Cd(,1-X)Mn(,X)Te and Cd(,1-X)Mn(,X)Se for x(, )< 0.30 and in Cd(,1-X)Mn(,X)S for x = 0.022 and 0.125. This spin-flip Raman scattering was observed for the temperatures range 1.8 K (LESSTHEQ) T (LESSTHEQ) 160 K and for magnetic fields (LESSTHEQ) 60 kG. The large measured spin-flip energies result from the exchange coupling of the electron with the Mn('2+) ions. Finite Raman shifts are observed in the absence of a magnetic field and are attributed to the bound magnetic polaron and thermal fluctuations in the local magnetization. The temperature and magnetic field dependence of the spin-flip energies and polarizations are compared with a statistical-mechanical model, the agreement is good for x(, )< 0.15.; Raman scattering from the vibrational modes in Zn(,1-X)Mn(,X)Te has been studied. The low frequency two-phonon density of states features exhibit a composition dependence. Low frequency disorder induced one-phonon density of states features are also present for x (GREATERTHEQ) 0.10. The optical phonons of Zn(,1-X)Mn(,X)Te exhibit a variation with x that is intermediate to the two-mode and one-mode situations. The optical modes of Zn(,1-X)Mn(,X)Te are compared with those of Cd(,1-X)Mn(,X)Te, and a random element isodisplacement model is used to describe the behavior of the optical phonons of both alloy systems.