Diluted magnetic semiconductors

The optical properties of the diluted magnetic semiconductor Zn1-x MnxS have been studied by using photoluminescence emission, lifetime and excitation spectroscopies. In photoluminescence spectroscopy three bands were found peaking at 585 nm (yellow band), 650 nm (orange band) and 750 nm (red band). For the yellow and red bands the peak position changes little with Mn concentration. For the orange band the peak energy decreases with increasing Mn concentration. The lifetimes of the yellow, orange and red bands were found to be about 70, 50 and 7 mus. The results of the lifetime measurements support the assumption that there is energy transfer from the yellow to the red band through radiationless transitions. In the excitation spectroscopy of the yellow band four peaks were found peaking near 526, 487, 461 and 426 nm. These four bands have been ascribed to transitions from the four lowest excited states of Mn ++ to the ground state. (Abstract shortened with permission of author.)

Zinc(1-x)manganese(x)sulfur is a ternary semiconductor compound which belongs to the family of diluted magnetic semiconductors (DMS). It has two crystalline phases: cubic for x < 0.10, and hexagonal for 0.10 < x < 0.50. Its energy gap is temperature and x dependent. The gap, ranging from 3.7 to 3.8 eV, is the largest of the DMS. These properties allow studies of the energy levels of the Mn^2+ ions in ZnS and their internal or ion-to-band transitions, by using photoluminescence. Samples with x = 0.01-0.50 were excited with the 5145A line of an Ar+ laser. The spectra, taken at temperatures between 10 and 300K, showed three bands: a band peaking at 2.12 eV was related to the 4T1 to 6A1 internal transition; a band peaking at 1.95-2.10 eV (depending on T) was related to the 4T1 to Gamma 1 5 ion-to-band transition; the origin of the third band, peaking at 1.65 eV, was discussed. A partial fourth band in the IR region was detected. The position of the 6A1 state with respect to the valence band was established.