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The structure of the previously reported InGaAsP two-wavelength demultiplexing photodetector has been inverted to circumvent fabrication problems associated with dissolution of the lower-bandgap quaternary layer during the LPE growth of subsequent higher bandgap layers. In addition, lower doping levels have been achieved in the LPE layers. The result of these modifications has been devices with greatly improved optical and electrical characteristics. The long-wavelength cutoff has been extended to 1.6 μm.