BAND ALIGNMENT AND BARRIER HEIGHT CONSIDERATIONS FOR THE QUANTUM-CONFINED STARK-EFFECT

Strained-layer multiple quantum wells InAsP/InP and InAsP/InGaP optica l modulators based on the quantum-confined Stark effect have been fabr icated from layers grown by metalorganic vapor phase epitaxy on InP(00 1). The device layers have been characterized by complementary high re solution x-ray diffraction, transmission electron microscopy, optical absorption and photoluminescence analyses. The structural properties o f the layers were deduced from the above data and an accurate determin ation of the band alignment of the heterostructures was made by perfor ming multiple transition fits to the optical absorption spectra using the Martin-Bastard envelope function model for strained-layer superlat tices. The electric held-dependent redshift of the fundamental electro n-heavy hole transition was measured by a photocurrent method and foun d to be enhanced for structures with lower valence band barrier height s. This observation leads directly to the conclusion that the overall performance of high speed, low drive voltage optical modulators may be improved by engineering the band alignment of the multiple quantum we ll stack towards structures with disproportionately large conduction b and offsets. An optimization of the band alignment will permit more ef ficient optical modulation by reducing the drive field required to ope rate the device, which, in turn, can have direct effects upon the driv e voltage, device capacitance, attenuation coefficient, and optical co upling and propagation losses. (C) 1998 American Vacuum Society. [S073 4-2101(98)04102-5].