Two-dimensional rough surface couplers for broadband quantum-well infrared photodetectors

Rough surfaces are proposed as a class of couplers for achieving high absorption in broadband quantum-well infrared photodetectors (QWIPs). The performance of these structures is predicted numerically using the steepest-descent fast-multipole method, a recently developed fast electromagnetic analysis technique. This method permits the efficient and accurate solution of the electric-field integral equation governing scattering from a quasiplanar structure. The scattered optical electric-field component along the growth direction at the device layer can be used to predict the QWIP absorption. It is demonstrated that rough-surface couplers exhibit very high absorption sustained over large spectral ranges, in contrast to quasirandom or periodic gratings that are characterized by tradeoffs between peak absorption and spectral range. It is expected that the excellent spectral absorption characteristics of rough-surface couplers will make them particularly suitable for broadband QWIP applications.