The electroluminescence of reverse biased Schottky diodes formed from ZnSe monocrystals doped with Mn, Al, and I is discussed. It is experimentally demonstrated that electroluminescence of Mn and of the self‐activated centres caused by doping with Al and I is excited by direct impact of hot electrons with energies lower than the band gap. Hot electrons are generated in reverse biased Schottky‐contacts dominated by an almost monoenergetic injection of primary carriers due to pure field emission. The current transport mechanism of Au‐ and Hf‐ZnSe diodes made on heavily doped ZnSe crystals is analyzed.
Two thresholds are relevant for the mechanism of impact excitation in thin film ELD's: The field strength Et at which tunnel emission from the interface states (IS interface of the MISIM structure) starts and the field Ea, above which electrons are loss‐free (ballistically) accelerated. It was previously shown, that Al2O3‐ZnS:Mn‐Al2O3 implement the case Et > Ea – every tunnel‐emitted electron immediately becomes hot. Replacing ZnS by ZnSe in otherwise identical structures reverses the relation (Ea > Et) – rather cold electrons are transferred. The experimental verification is twofold, by (time‐averaged) efficiency measurements and by the time resolved behaviour of current and brightness within one (every) excitation period.
The properties of ac driven thin film devices using ZnSe:Mn instead of ZnS:Mn as semiconductor layer are assessed. The principal advantage of low threshold is offset by inherent inefficiency of the temperature quenched Mn2+‐emission in ZnSe. No hysteretic behaviour could be obtained in structures otherwise identical to hysteretic ZnS ac TFDs. A rather interesting inversion in runaway and carrier injection thresholds for ZnSe relative to ZnS devices can be supposed.
Tunneling transport has been realized in plasma‐oxidized ultra‐thin film MIM structures on the basis of Al2O3 with thicknesses between 15 and 30 Å. Current–voltage measurements at 77 °K and higher temperatures have been performed up to electric fields of F ≦ 2 × 107 V/cm. A quantitative description of the results is given on the basis of Fowler‐Nordheim tunneling.
The Monte‐Carlo simulation of beam flux distribution of molecular‐beam epitaxy sources is extended to the region, where intermolecular collision cannot be neglected. When the mean free path becomes very small in comparison to the source dimensions, a effective source length will introduced to reduce the calculating time extremely. The similarity between the result of the simulation, the particle number profile, and the object of digital image processing is discussed. A method of digital image processing is used to reduce the calculating time and to improve the accuracy of the simulation with experiment. The average filter in real space is useful for successfully image filtering.
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