The effects of rapid thermal degradation of normalInP substrate on the quality of epitaxially grown layers are generally underestimated. Scanning photoluminescence, photocurrent, and etch pitting techniques have been used to evaluate the influence of normalInP substrate decomposition on the quality of epitaxially grown layers. Growth on substrates protected with an normalInP cover piece results in epitaxial layers with localized regions of low luminescence and high dislocation density. These are present even in layers with a very good surface morphology. The use of source‐piece protection, in conjunction with a shallow In meltback prior to epitaxy, eliminates the deleterious effects of thermal decomposition. The incorporation of these steps into the growth of device wafers greatly improves the yield of normalInP/normalInGaAsP light emitting diodes.

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Infrared-to-visible wave-length conversion in the Yb ¿· -Er ¿· doped phosphors system has been described by a simple three level model based on two ions mechanism. The excitation in the range of 900-1000 nm of an IR-photon is first absorbed by Yb ¿· ion as a sensitizer attributed to the resonant energy transition in Er ¿· ion from Ë ¿ ¾ Á ½ ¾ and ¾ Á ½ ¾ , respectively for green and red emission. The essential energy transfer processes in this system i.e. upconversion from Á ½½ ¾ and Á ½¿ ¾ , cross-relaxation from Ë ¿ ¾ and ¾ are taken into account. The limitations of the rate-equation approach are examined with a focus on the underlying dynamics of this rare-earth system.