INTRASUBBAND PLASMONS AND OPTICAL-TRANSMISSION IN RANDOM-LAYER-THICKNESS N-I-P-I SEMICONDUCTOR SUPERLATTICES

We investigate theoretically the intrasubband collective plasmon modes and the optical transmission in a specially constructed semiconductor superlattice consisting of n- and p-type doped semiconductors separat ed by an undoped intrinsic (i) semiconductor. The thicknesses of the c onstituent layers are randomly distributed in accordance with a design ed probability, and all of them are assumed to be sufficiently large s o that the quantum-size effect can be ignored. The materials of the la yers are characterized by frequency-dependent dielectric functions. Th e discontinuity at the interfaces is dealt with by using the transfer- matrix method. The calculation of dispersion relation and optical tran smission shows that in varying the degree of thickness randomness, the frequencies of the plasmon modes only exhibit small shifts, but the t ransmission coefficients are changed. A particular random structure is found in which some modes of electromagnetic waves with special frequ encies are completely unscattered by the randomness, whereas the other modes rapidly decay. This provides a possibility of building a high-q uality optical filter.