Abstract

Wavelength-division multiplexing is a technique that may be used to improve the efficiency, and increase the utility, of lightwave systems by expanding the information transmission rate without increasing the bit rate.^1,2 Recently, we have reported a new device that uses stacked eiptaxial InGaAsP layers to integrate both detection and demultiplexing functions into a single photodetector.^3,4 A difficulty in the fabrication of this structure results from dissolution of the lower-bandgap quaternary layer during the LPE growth of subsequent higher-bandgap layers. Further the dissolution is most severe for quaternary layers with bandgap energies smaller than 1.0 eV, and this has restricted operation of these devices to wavelengths ⪝ 1.25 µm. In this paper we will describe an "inverted" structure that has successfully eliminated this problem. Coupled with the achievement of lower doping levels in the LPE layers the resulting new structure exhibits substantial improvements in both the optical properties (quantum efficiency, optical cross-talk, long-wavelength cutoff) and the electrical properties (modulation bandwidth, electrical cross-talk).

© 1980 Optical Society of America