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p-n junction diodes were made from AlAs-GaAs mixed crystals of graded composition (energy gap). The energy gap vs composition was determined from measurements of the diode band-edge emission peaks vs electron microprobe analysis of p-n junction composition. A linear energy-gap variation was observed throughout the composition range 0–0.45 mole fraction AlAs. Measurements of the injection-current dependence and the temperature dependence of the emission spectra of these diodes, interpreted according to a simple model of injection electroluminescence, indicate that the AlAs-GaAs mixed crystals are of direct band nature to at least 0.25 mole fraction of AlAs. Diodes of 0.40–0.45 mole fraction AlAs junction composition, i.e., in the vicinity of the ``direct-indirect'' crossover, produced emission which requires more complex analysis.
Ku et al. (Thu,) studied this question.