Photoluminescence of ZnSe/ZnMnSe superlattices under hydrostatic pressure

Photoluminescence near 4450 Å (violet) and 5900 Å (yellow) from ZnSe/Zn_1-xMn_xSe strained-layer superlattices (SLS) is studied as a function of applied hydrostatic pressure up to ∼90 kbar for x=0.23, 0.33, and 0.51 at 9 K. For each of the three SLSs, the peak energy of the near-band-gap violet photoluminescence (PL) from exciton recombination increases sublinearly with pressure, and closely follows that of ZnSe. The observed dependence is consistent with type-I band alignment, at least at pressures where the violet PL intensity remains strong. For the x=0.23 SLS, the energy of the biexciton PL increases faster than that of the exciton, which suggests decreased confinement. The yellow PL is due to the ⁴T ₁ →⁶A₁ intraionic transition in Mn ²⁺ and the nearly linear decrease of the peak energy of this signal with pressure is explained by crystal-field theory. In most cases examined, the intensities of the violet and/or yellow PL decrease abruptly above a certain pressure that increases with x from ∼65 to ∼90 kbar. For the different cases, this suggests either the occurrence of a phase transition in the Zn _xMn_1-xSe layers or a band crossing.