Direct Current Electroluminescence in Rare-Earth-Doped Zinc Sulphide)

Some of the properties and characteristics of rare-earth-doped zinc sulphide DCEL devices are reported. Two types of devices are discussed, co-evaporated ZnS: RE thin films and ion implanted 2nS:RE single crystal diodes. The thin film devices exhibit bright DCEL of various colours at low applied voltages (typically ≈ 12 V). A study of the spectral intensities and lifetimes of the Er3+ ion in ZnS: Er3+ thin films is consistent with a Boltzmann energy distribution amongst the conduction electrons present in these devices. The ZnS:RE single crystal diodes fabricated in this laboratory by ion implantation are also capable of various colour DCEL. By comparing the EL emission obtained from the different rare earth dopants, erbium and neodymium are identified as the most efficient luminescence centres. Further consideration of the EL emission spectra gives evidence for the presence of inter-conduction band hot electron transitions in those devices containing rare earth dopants which are inefficient electroluminescence centres. These findings ran be explained in terms of Auger processes occurring in rare earth complexes.