Two-dimensional rough surface couplers for broadband quantum-well infraredphotodetectors

Rough surfaces are proposed as a class of couplers for achieving high absor ption in broadband quantum-well infrared photodetectors (QWIPs). The perfor mance of these structures is predicted numerically using the steepest-desce nt fast-multipole method, a recently developed fast electromagnetic analysi s technique. This method permits the efficient and accurate solution of the electric-field integral equation governing scattering from a quasiplanar s tructure. The scattered optical electric-field component along the growth d irection at the device layer can be used to predict the QWIP absorption. It is demonstrated that rough-surface couplers exhibit very high absorption s ustained over large spectral ranges, in contrast to quasirandom or periodic gratings that are characterized by tradeoffs between peak absorption and s pectral range. It is expected that the excellent spectral absorption charac teristics of rough-surface couplers will make them particularly suitable fo r broadband QWIP applications. (C) 1998 American Institute of Physics. [S00 03-6951(98)01650-7].