Raman spectroscopy of two novel semiconductors and related superlattices: Cubic Cd1−xMnxSe and Cd1−xZnxSe

Abstract

The Raman scattering from ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Zn}}_{\mathrm{x}}$Se and ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Mn}}_{\mathrm{x}}$Se, grown by molecular-beam epitaxy on (001) GaAs substrates, shows zone-center optical phonons characteristic of a zinc-blende structure, indicating that these epilayers represent the cubic phase of these materials which in the bulk crystallize only in the wurtzite form. The variation of the frequency of the zone-center optical phonons as a function of composition x shows a ‘‘two-mode’’ behavior in ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Mn}}_{\mathrm{x}}$Se and a pattern inter- mediate between ‘‘two-mode’’ and ‘‘one-mode’’ in ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Zn}}_{\mathrm{x}}$Se. The modified–random-element–isodisplacement model provides a satisfactory basis for these patterns. In the case of ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Mn}}_{\mathrm{x}}$Se, the large Raman shifts associated with the spin flip of donor-bound electrons and the huge Zeeman shifts of an excitonic component observed in photoluminescence (including saturation at high magnetic fields and low temperatures), show that the large sp-d exchange interaction characteristic of diluted magnetic semiconductors is manifested also in the zinc-blende phase of this alloy.