A new vertically illuminated photodetector design that eases the bandwidth-efficiency limitation of conventional photodiodes for long-wavelength applications is reported. This detector design incorporates dual absorption regions and a wide bandgap drift enhancement layer for high speed and efficiency. Theoretical models indicate that this design can achieve a bandwidth-efficiency product (BWE) as high as 26 GHz for top-illuminated single-pass structures with 6-/spl mu/m optical window and 50-/spl Omega/ load resistance. This represents an improvement of 24% over the BWE achievable in conventional top-illuminated PIN diodes. A through-wafer-illuminated two-pass design can improve the BWE to 35 GHz (an improvement of an additional 35%). Single-pass top-illuminated photodiodes have been fabricated using this design; a bandwidth of 30 GHz and responsivities of 0.82 A/W have been achieved, for a BWE of 19.7 GHz. The BWE of these first-generation devices is limited by anode series resistance. This detector design offers performance suitable for bit rates of up to 40 Gb/s in a simple, normal incidence photodetector design.