Semiconductor device including cascadable polarization independent

Abstract

Polarization independence and higher intrinsic speed resulting from lowered device capacitance are achieved in a modulation-doped semiconductor heterostructure wherein a transfer barrier region including a graded bandgap semiconductor layer facilitates flow of carriers (electrons) from a doped reservoir to a narrow bandgap active region while an isolation barrier region confines carrier flow to be substantially within the graded bandgap region and the associated active region to minimize leakage current. The present modulation-doped heterostructure exhibits substantially equal end-boundary conditions in an unbiased condition for efficient cascading or stacking with additional modulation-doped heterostructures. Several embodiments of the present invention are described in which grading in the transfer barrier region is shown to include substantially continuous compositional grading, stepwise compositional grading, and superlattice grading. In these embodiments, the thickness of the active region is determined in proportion to the size of the optical effect which is to be produced.