Intense blue-emission band and the fabrication of blue light emitting diodes in I-doped and Ag-ion-implanted cubic ZnS

The nature of the blue-emission bands appearing in highly conductive n-type and Ag-ion-implanted cubic ZnS with iodine (ZnS:1) has been investigated by means of time-resolved photoluminescence and electroluminescence measurements. It is found that the n-type crystal exhibits extremely efficient blue luminescence around 2.65 eV and involves two kinds of donor-acceptor pair transition in it. The Ag-ion-implanted crystal produces also the intense blue band at about 3.0 eV due to the electronic transition from the conduction band to the Ag acceptor level located at 0.6 eV above the valence band. A forward-biased electroluminescent diode capable of emitting bright blue emission bands at 2.9 and 2.7 eV, at room temperature, has been reproducibly prepared using Ag-ion implantation and subsequent recoil implantation techniques, and yields an external quantum efficiency of about percent. The results obtained can be compared with those in a Schottky-barrier diode (having a quantum efficiency of about 10^-2percent) made of Au electrode/n-ZnS:I crystal with cleaved