Mn Electroluminescent Devices Research Articles

Fundamental properties and application of Zn1−XMgXS:Mn thin film electroluminescent devices

By Mg doping of ZnS, the lattice constants and the band gap of Zn1−XMgXS host material were increased. The emission spectrum of Mn in Zn1−XMgXS shifted to shorter wavelengths than that of ZnS:Mn. The electroluminescent (EL) devices fabricated with the source of X=0.32 show 552 nm peak yellowish–green emission. Deposition conditions for the Zn1−XMgXS:Mn phosphor layer were optimized to obtain bright emission. As a result, the Zn1−XMgXS:Mn EL devices have a luminance of 282–333 cd/m2 which is as high as that of the conventional ZnS:Mn EL devices.

Uniform and filamentary transport in d.c. thin-film ZnS: Mn electroluminescent devices

Abstract Thin-film ZnS is highly insulating until the applied field rises above approximately 1 MVcm−1. The current then rises almost exponentially with increasing voltage, and current densities in excess of 1 A cm−2 2 can be maintained. If the ZnS is doped with Mn, the resulting efficient electroluminescence provides a means of spatially and temporally mapping the local current density. Device behaviour under both steady-state and non-equilibrium conditions has been investigated including laterally uniform current, filamentary current flow, kinetic electroluminescence and negative-capacitance behaviour. This behaviour is inconsistent with previously reported transport models but can be understood, at least qualitatively, within the framework of the novel high-field transport mechanism proposed. This is based on tunnelling from states within the bandgap and the dynamics of interacting regions of space charge within the ZnS.

Nonlinearity in the excitation yield of ZnS:Mn electroluminescent devices

Measurements of the excitation yield of ZnS:Mn electroluminescent devices are reported over a Mn concentration range of 0.2,...,1.1 mol %. They show a continuous increase in nonlinearity as the concentration is increased. This is attributed to the field dependence of the hot-electron impact efficiency and to the dependence of the nonuniform field profile on Mn content. This is directly relevant to the light-emitting performance of the devices.

Excitation efficiency of electrons in alternating driven ZnS: Mn electroluminescent devices

We measured directly the dependence of the manganese excitation efficiency η exc on the excitation level and compared it to the behaviour of the intrinsic broad band ZnS emission for two different kind of devices. In well prepared, optimized devices, η exc is constant up to the beginning of the saturation range. Within the saturation range, η exc decreases with increasing excitation level. In specially annealed devices with shallow interface states, however, η exc is very low at the electroluminescence threshold and increases strongly with the excitation level. In both kinds of devices, the ratio R of the broad band ZnS emission to the yellow Mn emission shows only a slight dependence on the excitation level. The results suggest that R cannot be taken as a criterion for the electron energy distribution.

Effect of Mn concentration on electron excitation in ZnS: Mn electroluminescent devices

In activated phosphors such as ZnS: Mn the brightness varies with the concentration of the activator, in electroluminescence in another way than in photoluminescence. A model is presented that explains this on the basis of a quenching term and an excitation term involving electron interaction cross sections in Mn. The model is consistent with observed brightness data and supports the findings of other work in ZnS:Mn. An estimate of the low-energy electron interaction cross section of Mn ions suggests a strong interaction to take place.

Organized and semiorganized doping for ZnS:Mn electroluminescent devices

The potential to achieve nonrandom Mn doping in ZnS:Mn material is discussed. By making diffusion measurements, we determine the required conditions during growth and operation of ZnS:Mn devices that are compatible with nonrandom doping. The probability of forming nearest neighbors and nearby neighbors of Mn in ZnS is calculated for various doping schemes, and the impact of these arrangements on the brightness of electroluminescence and photoluminescence in ZnS:Mn is discussed.

Observation of double light pulses in thin-film ZnS:Mn electroluminescent devices

Thin-film ZnS:Mn electroluminescent devices can exhibit, under pulsed electrical excitation, a double light pulse, as has been previously observed in other phosphors. We specify the conditions under which this phenomenon appears and relate it to the basic mechanism of carrier emission in the active layer.

ZnS:Mn Electroluminescent Device Prepared by Metal-Organic Chemical Vapor Deposition

AC thin-film ZnS:Mn electroluminescent devices were fabricated by metal-organic chemical vapor deposition, using dimethylzinc and H2S as source gases and tri-carbonyl-methyl-cyclopentadienyl-Mn as the dopant gas. Tri-carbonyl-methyl-cyclopentadienyl-Mn was decomposed by heating at 580°C at the entrance of the reactor, enabling the ZnS film to be doped homogeneously with the optimum concentration of Mn. The brightness of metal/insulator/semiconductor electroluminescent devices made with the resulting ZnS:Mn film was more than 5000 cd/m2 (5 kHz, 130 V), while metal/insulator/semiconductor/insulator electroluminescent devices had a brightness of more than 6000 cd/m2 (5 kHz, 160 V) and exhibited hysteresis in their brightness-voltage characteristics.

AC-Thin Film ZnS:Mn Electroluminescent Device Prepared by Metal Organic Chemical Vapor Deposition

AC-thin film ZnS:Mn electroluminescent devices are fabricated by the Metal Organic Chemical Vapor Deposition, using dimetylzinc and H2S as source materials. The crystal structure of the MOCVD-prepared ZnS film on glass is (111)-oriented cubic polycrystalline. The electroluminescent center Mn is added into MOCVD-prepared ZnS film through thermal diffusion. The brightness and efficiency of the MOCVD-prepared EL devices are higher than those of the EB-evaporation prepared EL devices having the same structure. The MOCVD-prepared EL devices exhibit few dark spots, and therefore exhibit high stable operation and high breakdown voltage.