The combination of wafer soldering using metal layers and the introduction of buried micro-reflector structures has proven to be a promising approach to fabricate high brightness, substrate-less LEDs in the AlGaInP material system. In addition to the enhanced light output, the scalability of this approach has been predicted as a major advantage. In contrast to other approaches, larger area LEDs can be fabricated without altering the epitaxial structure and thickness of layers simply by offering a larger area for light generation. First samples of amber (λ = 615 nm) buried micro-reflector LEDs with side-length up to 1000 µm have been realized. Devices mounted in packages with improved heat sinks are capable of low voltage CW operation with currents as high as 600 mA (V fw ≤ 2,8 V) without significant thermal flattening of the light-current characteristics. The maximum luminous flux achieved at these operating conditions is 46 lumen. Already these first experiments demonstrate the potential of the concept of buried micro-reflector LEDs not only for high-brightness but also for high-current operation. The results are among the best values of high-flux LEDs in this wavelength range.
Thin film bilayers of metal and amorphous chalcogenides have been prepared by evaporation. The metals were silver and zinc, while the chalcogenides were P2Se3 and arsenic sulphides, mainly As2S3. The metals dissolved into the chalcogenide films when illuminated with ultraviolet light or when irradiated with an electron beam. The changes in composition and chemical bonding which were caused by this irradiation, were investigated by x-ray photoelectron spectroscopy. The concomitant structural changes have been investigated by electron diffraction.After the metal and chalcogenide had intermixed, either due to photon or electron irradiation, the layers became sensitive to an electron beam; this sensitivity depended on the composition of the chalcogenide. Energy-dispersive x-ray microanalysis showed that the electron beam rapidly, but reversibly, depleted the irradiated areas of the dissolved metal. Very fine patterns, of better than half-micron resolution, could be written. By exposing a pure arsenic sulphide film through a shadow mask to ultraviolet light, zinc could be deposited selectively to form fine patterns. Plasma processing developed either kind of pattern reliably, thus rendering the material a dry inorganic resist for photo- and electron-beam-lithography with potential benefits in particular for GaAs.
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